The Panda Paradox

Zoologists classify the panda as a carnivore.
The panda has gut structure, gut function, and gut enzymes like a carnivore.

The panda does not have multiple stomachs, nor an enlarged cecum, nor the gut microbes found in animals that eat diets composed largely of fiber, like cattle and sheep.

A study published in the Proceedings of the National Academies of Science states:  "The giant panda genome codes for all necessary enzymes associated with a carnivorous digestive system but lacks genes for enzymes needed to digest cellulose, the principal component of their bamboo diet."

Source:  Wikimedia

Yet wild giant pandas consume around 20-40 pounds of highly fibrous bamboo stalks and leaves every day.

The San Diego Zoo states that the small Red Panda's diet is 95 percent bamboo.

The Smithsonian National Zoo states that "A wild giant panda’s diet is almost exclusively (99 percent) bamboo."

At the Talk Origins site on human evolution, Douglas Theobald, professor of biochemistry at Brandeis University writes "... even though humans are herbivorous, the small human caecum does not house significant quantities of cellulase-excreting bacteria, and we cannot digest more than but a few grams of cellulose per day."  [Emphasis added]

Leaving aside for the moment the interesting fact that this staunch defender of evolutionary theory describes humans as herbivorous, the panda's ability to digest cellulose is similar to humans.   The gut microbes of pandas digest very little of the fiber the pandas consume; 92 percent of cellulose a panda ingests ends up eliminated in its feces.

If in pandas gut microbes convert only 8 percent of ingested cellulose into short chain fatty acids, this probably means that the panda gets most of its energy from the digestible carbohydrate and protein provided by bamboo leaves and stalks, not from fat.  Does the panda challenge the idea that "the natural diet of mammals is a high-fat diet"?

The pandas provide a striking example of a non-human mammal that has almost none of the genetic or physiological equipment associated with herbivory (only having some dental and grip adaptations), yet it spontaneously lives as an herbivore.

It is believed that the first giant panda ancestor to include some bamboo in it diet was Ailuropoda micrta which existed about 3million years ago.  This species appears to have descended from the primal panda, Ailuaractos Lufengensis, an arctoid with a carnivorous diet. The carnivorous arctoids appear first in the evolutionary record about 46 million years ago. 

The fact that a member of the Carnivora order has adapted spontaneously to a highly specialized and extremely fibrous, low fat, 99% herbivorous diet without apparent major physiological and genetic changes seems to raise some interesting questions for those who believe that modern humans are optimally adapted to some diet consumed by some paleolithic human ancestors.

The panda also seems to challenge another presupposition of paleolithic diet theory, which goes something like this:  Any species that at any time in its evolution adopts a meat-based diet is required thenceforth to always maintain a meat-based diet to sustain health. 

This is clearly not true for the panda; despite having physiological equipment that limits its ability to extract nourishment from plants, it has succeeded in its niche for at least a million years. 

The panda shows us that when individuals of a species encounter an environmental challenge, they do whatever they can do to succeed in the changing environment without any concern about what their ancestors did, or whether they have the optimal physiology for the new habit.  The new feeding strategy may not be optimal, and it doesn’t have to be; it only has to be good enough to allow individuals to survive long enough to reproduce.

Now, why does Professor Theobald say that humans are herbivorous?  Because we humans have descended from a very long line of herbivorous ancestors and have a body displaying more features in common with other herbivores than with carnivores, including plantigrade stance, relatively slow sprints (compared, for example, to canines or felines), color vision, nails (rather than claws), small mouth, fleshy lips, non-shearing teeth, carbohydrate taste receptors (rather than amino acid taste receptors found in cats), non-expandable esophagus, haustrated and long intestines, low potency bile, a vermiform appendix,  and a sense of fear (those at the top of the food chain are not stalked so do not need fear to enhance survival). 

During the last two to four million years, climate changes and migrations put human ancestors in environments where they had to adopt omnivorous diets to survive, despite not being fully adapted to the new foods (meat and animal fat), just as the first panda ancestor to eat bamboo was not fully (physiologically) suited to a bamboo diet.  Nevertheless, just as the bamboo diet was/is good enough for the panda lineage to survive, a meat-based diet was/is good enough for the human lineage to survive in plant-food depleted environment.

That does not mean it will produce the best health.  A diet does not have to protect individuals from heart disease or cancer, or support maximum longevity, to be good enough to support the continuation of the species.  These diseases typically kill people long after they have reached reproductive age. 

The discordance hypothesis favored by some Paleolithic diet advocates states that diseases arise as a consequence of an individual adopting a diet, lifestyle, or habitat sufficiently different from the diet, lifestyle, or habitat of its ancestors to create a discordance with the genetic heritage of its species.

The wild giant panda seems to have a diet substantially discordant with its genetic constitution.  Yet the panda doesn’t suffer from a host of diet-induced diseases.

Pandas in captivity eat a diet perhaps more discordant with the ancestral panda diet. According to this report of captive giant panda diets in five Chinese facilities:

“Each facility feeds a steamed grain mixture comprising 13–56% of the diet on an as-fed basis, animal products (milk, eggs, and/or meat; 8–25% of the diet), and bamboo (17–82% of the diet). Seasonally available fruits and/or vegetables are sometimes included (0–29% of the diet).”

This mixed and cooked diet deviates from the 100% raw, 99% bamboo diet of wild giant pandas, and includes foods never eaten by wild pandas during the past 3 million years (grains).  The San Diego Zoo  reports:

“At the San Diego Zoo, pandas are offered bamboo, carrots, yams, and special leaf eater biscuits made of grain and packed with all the vitamins and minerals pandas need.”

It seems the San Diego veterinarians have settled on a vegan diet for the panda.  The pandas apparently do quite well on this non-ancestral diet, at least in terms of longevity.  According to the SanDiego Zoo, wild pandas live only 14-20 years, but pandas in zoos live 30 years, 50 to 100 percent longer.  Apparently, a panda can live much longer when eating an evolutionarily novel diet including steamed grains than when eating only the raw foods eaten by its wild ancestors.  This experiment apparently trumps the discordance hypothesis.

Consider that the panda has been isolated to a bamboo forest, and eating a bamboo-based diet, for perhaps one million years, yet this sustained selective pressure to adapt to a bamboo diet has had relatively little impact on its basic anatomy and physiology. Today’s panda still does not have an herbivorous body form despite such a long period of evolution on the 99% bamboo diet, but the diet works good enough for the panda (perhaps as good as it gets in the current niche) to pass the bamboo habit to the next generation.

In contrast, the past two million years of human evolution occurred under much more varied ecological conditions. During human ancestral evolution, the variability of the ice age climate and human mobility led to wide variability of plant-animal ratios in ancestral diets, and this combined with intertribal marriages tended to minimize selective pressures for any specific physiological adaptations to meat-eating and supported retention of the basically herbivorous primate physiology. 

The panda seems to challenge the idea that our genes, or the diets of our remote ancestors, determine the optimal diet for present-day humans.  Apparently neither ancestral diets, nor genes, nor physiological equipment will necessarily make a meat-based diet a perpetual requirement, or the optimum choice, for any given species, let alone one (such as humans) with an extensively herbivorous ancestry and numerous adaptations to herbivory. 

I think the panda shows us quite clearly that if we want to know how to prevent degenerative diseases and maximize healthy longevity, we will want to gather knowledge from the experience and experiments (natural and controlled) of present day humans, rather than assume that we will get the best results by eating only the foods consumed by our remote ancestors.

Post Script

This post was inspired by similar, but less dramatic examples of non-human animals adapting to non-ancestral foods/diets in some Plant Positive videos, for example:

Primitive Nutrition 60:  Ketosis Is Natural. Natural Is Good. Part III

"Polar bears in captivity are not fed a diet like they would consume in the wild.  They are actually fed fruits and vegetables.  But this isn’t their natural diet!  Surely this is a form of animal abuse, right?"

"Actually, polar bears in captivity live considerably longer.  But shouldn't an evolutionarily novel diet destroy their health?  This is yet another example of how Paleologic is no substitute for experiment and observation."

From Polar Bears International:

"In the wild, polar bears live an average 15 to 18 years, although biologists have tagged a few bears in their early 30s. In captivity, they may live until their mid- to late 30s. Debby, a zoo bear in Canada, lived to be 42."

 Thus, an evolutionarily novel diet supports a doubling of lifespan in polar bears.

Thanks to Plant Positive for giving inspiration and sharing suggestions for this post.

Vitamin B12 and Human Nutritional Evolution

I once believed and argued that the fact that humans require vitamin B-12 provided substantial support for the idea that humans have a biological requirement for dietary meat.  My reasoning went thus:

Humans require vitamin B-12, and only animal products reliably provide natural bioactive vitamin B-12, therefore we must be adapted to and dependent upon meat-eating.

I have since realized that I made a few mistakes here.  Although we definitely require B-12, animal products are not the only reliable sources of natural bioactive B12, and human B-12 metabolism provides evidence that our ancestors adapted to an environment/diet that had a low availability of B-12 compared to currently recommended daily reference intakes.

Human B-12 Metabolism

Humans have enterohepatic circulation of vitamin B-12.[1 ] As noted by Herbert [2 ], this can allow an initially B-12 replete adult go 20-30 years without vitamin B-12 intake:

“The enterohepatic circulation of vitamin B-12 is very important in vitamin B-12 economy and homeostasis (27). Nonvegetarians normally eat 2-6 mcg of vitamin B-12/d and excrete from their liver into the intestine via their bile 5-10 mcg of vitamin B-12/d. If they have no gastric, pancreatic, or small bowel dysfunction interfering with reabsorption, their bodies reabsorb ~3-5 mcg of bile vitamin B-12/d. Because of this, an efficient enterohepatic circulation keeps the adult vegan, who eats very little vitamin B-12, from developing vitamin B-12 deficiency disease for 20-30 y (27) because even as body stores fall and daily bile vitamin B-12 output falls with body stores to as low as 1 mcg, the percentage of bile vitamin B-12 reabsorbed rises to close to 100%, so that the whole microgram is reabsorbed.”

What kind of environment/diet would naturally favor the survival of humans having such efficient recycling of vitamin B-12 but not of other B-complex vitamins? 

As a general principle, if an organism subsists on a diet with a low availability of a certain essential nutrient, it needs mechanisms for increasing absorption and retention of that nutrient, to prevent deficiency.  On the other hand, if an organism subsists on a diet with a very high availability of a certain essential nutrient, then it needs mechanisms for reducing absorption, detoxifying, and eliminating that nutrient.

Put in natural selection terms, only an ancient environment/diet with a low B-12 availability would have favored the survival and reproduction of humans who could recycle B-12 very efficiently.  An ancient environment/diet with a high B-12 availability would have made such a capacity unnecessary; on the contrary, an environment with a high availability of vitamin B-12 would have favored those who were less efficient at using B-12, or those who deliberately excreted excessive B-12 (in order to prevent B-12 accumulation and toxicity).

Thus, modern human B-12 metabolism suggests that modern humans are adapted to a diet that provides B-12 in less than required amounts on a daily basis, while occasionally providing larger doses in excess of requirements.  

Currently the National Academy of Sciences recommends that adults consume 2.4 mcg of B12 daily.  They calculated that this covers the needs of 98 percent of individuals, but most of us require less than this.  The following table shows the B12 contents of commonly consumed animal products:

Three ounces of beef or salmon provides the recommended intake, and three ounces of shellfish substantially exceeds the recommended 2.4 mcg.  In contrast, one would have to consume 24 ounces of chicken or turkey daily to ingest 2.4 mcg of B12. 

Non-animal B-12 Sources

As I said above, I previously accepted that only animal products reliably provide natural vitamin B-12.  Although this is a common belief, and probably a good general rule in modern industrialized nations, I think we have significant evidence that pre-industrial humans had other significant sources of vitamin B-12.

First, although animal products provide the most common vector for delivery of B-12 in modern industrialized nations, only microbes produce vitamin B-12. [3] Many microbes have the ability to produce B-12, among them the following genera: Aerobacter, Agrobacterium, Alcaligenes, Azotobacter, Bacillus, Clostridium, Corynebacterium, Flavobacterium, Micromonospora, Mycobacterium, Norcardia, Propionibacterium, Protaminobacter, Proteus, Pseudomonas, Rhizobium, Salmonella, Serratia, Streptomyces, Streptococcus and Xanthomonas. 

Bacillus megaterium is a common soil bacteria, not pathogenic to humans, and a producer of vitamin B-12.[4]  According to Patricia Vany of the Department of Biological Sciences at NIU, B. megaterium occurs in human breast milk.[15, third slide] 

Lactobacillus reuturi, a member of the gastrointestinal ecosystems of humans, poultry, swine, and other animals, and present in sourdough culture, produces vitamin B-12. [5]

Albert et al reported “the human small intestine also often harbours a considerable microflora and this is even more extensive in apparently healthy southern Indian subjects. We now show that at least two groups of organisms in the small bowel, Pseudomonas and Klebsiella sp., may synthesize significant amounts of the vitamin.”[6]

In 1995 Suzuki reported that the marine algae, nori, prevented all signs of B12 deficiency symptoms in 6 vegan children he studied:

“A nutritional analysis was conducted on the dietary intake of a group of 6 vegan children aged 7 to 14 who had been living on a vegan diet including brown rice for from 4 to 10
years, and on that of an age-matched control group. In addition, their serum vitamin B12 levels and other data (red blood cell count, hematocrit, hemoglobin, etc.) were determined in the laboratory. In vegans' diets, 2-4 g of nori (dried laver), which contained B12, were consumed daily. Not a single case of symptoms due to B12 deficiency was found. There were no statistically significant differences between the two groups with respect to any of the examination data, including B12 levels (p < 0.05). Therefore, consumption of nori may keep vegans from suffering B12 deficiency.” [7] 

[In 2005 Croft et al reported that algae acquire vitamin B12 through a symbiotic relationship with bacteria. (14) ]

In 2009 Koyyalamudi et al [8] reported that the common white button mushroom can provide vitamin B12 of value equivalent to that found in beef, beef liver, salmon, egg, and milk (not analogues).  Koyyalamudi et al determined that the mushrooms probably absorbed the B12 from bacteria inhabiting their growth medium:

“High concentrations of vitamin B12 were also detected in the flush mushrooms including cups and flats.  HPLC and mass spectrometry showed vitamin B12 retention time and mass spectra identical to those of the standard vitamin B12 and those of food products
including beef, beef liver, salmon, egg, and milk but not of the pseudovitamin B12, an inactive corrinoid in humans. The results suggest that the consumer may benefit from the consumption of mushroom to increase intake of this vitamin in the diet.” [8]

In 1994, Mozafar reported that spinach leaves and barley seeds grown on soil fertilized with organic matter or isolated B12 take up vitamin B12 into their tissues from the soil.  The spinach leaves and barley kernels were thoroughly washed with distilled water before being tested for B12 content, so this was not a case of finding B12 on soiled plants.  Their testing confirmed that these plants contained active B12, not inactive analogues.[9]

In summary, it appears that non-pathogenic soil microbes, human small intestinal bacteria, lactobacilli from fermented foods, some sea algae, common mushrooms, and plants grown on soil fertilized with animal manure can all can provide biologically active B12.   Any of these could have served as ongoing sources of B12 for prehistoric human ancestors, but modern circumstances may make these non-animal sources of B12 unreliable for modern humans.

I think it safe to assume that our prehistoric ancestors had more contact with soil than we do, sitting on it, sleeping on it, digging in it, and drawing water from sources in contact with the soil.  Humans like other primates are apt to touch their own lips from time to time, providing a vector by which soil microbes could enter the human gut.

Humans living in modern industrialized nations typically ingest multiple courses of oral antibiotics over a lifetime, reducing or eliminating the population of B12-producing bacteria residing in the small intestine.   All of our prehistoric ancestors would have been breast fed and probably kissed often, which transmits flora from one generation to another, and this transmission would not have been interrupted by antibiotic treatments.

Fermentation of plant foods, particularly fruits, occurs spontaneously in nature,  providing another route by which our ancestors may have ingested B12-producing lactobacilli.  Our ancestors almost certainly consumed any edible wild mushrooms and all of the plants they ate grew in soils teaming with bacteria and fertilized by fermented organic wastes, providing another B12 source.

All of this information suggests that modern hygiene, indoor lifestyles, antibiotics, and use of chemical rather than biomass fertilizers in farming have reduced the amount of B12 available to humans in modern urban environments from non-animal sources. 

Thus, the low availability of B12 from non-animal sources in modern urban environments is an artifact not reflective of preindustrial environments, and it appears probable that our prehistoric ancestors had more non-animal sources present in their environment, like the southern Indians studied by Albert et al.[6] 

My Fallacious Appeal to 'Nature'

When I previously argued that meat-eating is the 'natural' way to get B12, I committed the fallacy of appeal to nature. 


The problem here lies in these underlying assumptions:  1) all 'natural' behaviors are 'health-promoting' behaviors for modern urban humans,  and 2)  all 'unnatural' behaviors are unhealthful.

Consider these questions:

 

Is it natural for humans to wear clothing?  Does wearing clothing promote better health in some circumstances?  (Imagine people living in Minnesota rejecting clothing because their African ancestors didn't wear any.)

 

Is it natural for humans to live in igloos in the arctic circle?  Does living in igloos in the arctic circle promote the best of health?

 

Is it natural for humans to live in natural caves?  Do humans have the best possible health when living in natural caves?  Is a natural cave the best possible human shelter?

 

Is it natural for humans to commit homicide, engage in war, or eat human flesh?  Do any of these promote health? 

 

If all you mean by 'natural' is 'spontaneously occurring,' then all human behaviors are 'natural.' 

But is the 'natural' choice of our ancestors the best possible choice for modern humans of the present day?

Simply put, the fact that our ancestors did something then does not tell us that it is the best thing for us to do now.

The fact that our ancestors obtained B12 by a 'natural' route (eating meat) does not tell me that this is the optimal way for me to get B12 in our modern circumstances. 

The Nature of B12 Supplements

Artificial synthesis of B12 requires about 70 synthesis steps, making it impractical as a method for commercial production of B12.  “Therefore, today vitamin B12 is exclusively produced by biosynthetic fermentation processes, using selected and genetically optimized micro-organisms.” [10]

In other words, we cultivate, feed and breed living microbes so that they will produce the nutrient we want.  This practice seems similar to cultivating cattle to produce protein or B12.  If the former is ‘artificial,’ so is the latter.

Tablets of microbially synthesized B12, burgers of ground beef, capsules of vitamin D extracted from sheep’s hair, and tortillas made from corn are all end products of humans processing a raw material into a form that humans can conveniently consume.   If you reject B12 tablets as ‘unnatural,’ you should similarly reject ground beef burgers and vitamin D capsules.

The information above indicates that modern antibiotics and hygiene have reduced or eliminated intestinal flora that would otherwise produce B12 for us, and modern agricultural practices have reduced the B12 content of plant foods.  Similarly, modern indoor lifestyles have reduced our endogenous production of vitamin D.  We can reasonably use supplements to correct for these technology-induced deficiencies.

In short,  B12 supplements are the most reliable source of natural B12 in the modern environment.

Microbial B12 Supplements Recommended To People Past 50 Years Of Age

The Linus Pauling Institute at Oregon State University recommends that all people (including omnivores) over the age of 50 take a B12 supplement:

“Also, individuals over the age of 50 should obtain their vitamin B12 in supplements or fortified foods like fortified cereal because of the increased likelihood of food-bound vitamin B12 malabsorption.”[11]

In the publication Dietary Reference Intakes [12 ], the National Academy of Science Food and Nutrition Board concurs:

So these sources do not consider animal foods to be reliable sources of B12 for those of us more than 50 years of age.

Do we reject this advice because it is not 'natural' to take supplements?

Some B12 Options


Modern humans typically use their minds to identify their requirements for health and comfort, then develop and use appropriate technology to provide those requirements in the most efficient, safest possible way.  

Thanks to microbe-ranching, each modern urban human now has the opportunity to decide which of at least 3 courses s/he would prefer to take to ensure achievement of a healthy B12 status.

Course 1:  Obtain B12 directly from a cultivated microbial source, the production of which requires relatively little land and water and produces no urine or feces.  This source is free of saturated fats, cholesterol, heterocyclic amines, lipid peroxides, pathogenic organisms, or antigenic Neu 5Gc sialic acid (a suspect in human cancers and autoimmunity, found only in mammal’s products, 13 ).

Course 2: Obtain B12  from animal products, the production of which requires enormous amounts of land and water and produces tremendous amounts of urine and feces requiring safe disposal.  This source also supplies saturated fats and cholesterol,  heterocyclic amines (cooked meat), and lipid peroxides (cooked fat),  and is frequently contaminated with various potential pathogens (E. coli 0157:H7, MAR bacteria, salmonella, vibrio, etc.).  Red meats and mammalian milks also provide antigenic Neu5Gc sialic acid. [13]

As noted above, current science indicates that Course 2 is probably not reliable for people more than 50 years of age.

Course 3:  Use both B12 supplements and animal products.

Take your pick, or perhaps you will discover another way.

Thanks to the author/producer of the Primitive Nutrition video series for alerting me to the article on the B12 content mushrooms used in this post.

Strength Training May REDUCE Protein Requirements

Conventional wisdom maintains that people engaged in intense strength training have increased protein requirements making it necessary for them to consume more protein than untrained individuals.   I have believed this myself.

I just came across an elegant study by Moore et al [1] which produced evidence that a resistance training program may reduce protein requirements.

The Study Methods

Moore et al put 12 healthy untrained young males (20-24 years old) on a 12 week strength training program described thus:

“The 12-wk whole body resistance training program involved 13 guided-motion resistance exercises divided over 3 different training days, as previously described (8). Briefly, training days were divided into legs (leg press, leg curl, leg extensions, and standing calf raises), pushing exercises (seated military press, bench press, vertical bench press, chest fly, and seated machine triceps extensions), and pulling (latissimus pull-down, seated wide-grip row, seated narrow low row, and seated biceps curl) exercises. One repetition maximum (1 RM) was measured for each exercise before training and 2–4 d after the last training session to evaluate strength changes. Participants trained 5 d/wk at an initial intensity of ∼70% of the pretraining 1 RM with a goal of 2 sets of 10–12 repetitions during the first 2 wk. In wk 3–12, exercise intensity was adjusted to ∼80–85% 1 RM so that 3 sets of 6–10 repetitions were performed. All training sessions were supervised by a study investigator to ensure proper technique and exercise intensity adherence. Compliance with the training program in terms of attendance was >95% for all participants.”

Moore et al monitored the results of the training on body composition and protein metabolism using muscle biopsies, nitrogen balance markers (urinary, fecal, sweat and miscellaneous nitrogen losses), and blood assays.  They estimated dietary protein intake using diet records, except for 5 days before and during the final week of training, when the subjects received prepackaged meals of measured protein, fat, and carbohydrate content.  They maintained protein intake constant at ~1.4 g/kg/d for each subject.  Protein intake averaged 109-125 g per day throughout the duration of the study.

Unlike other studies of this type, Moore et al measured protein metabolism in both the fed and the fasting state.

Results

Over the course of the study, the subjects increased strength by 30-90% and gained an average of 2.1 kg bodyweight.  Lean body mass increased by ~2.8 kg (6 pounds) while fat mass decreased by ~0.9 kg (2 pounds). lean mass accrued at a rate of 233 g (~0.5 pound) per week, or 33 g (slightly over an ounce) per day, an amount undetectable on a day to day basis.  Muscle fiber cross-sectional area increased by about 50%.

Moore et al found that this 12-wk training program reduced whole body protein turnover, meaning, the training reduced whole body protein breakdown and synthesis.  Although this might surpise some people, they refer to five studies showing that “resistance exercise is a potent anabolic stimulus that increases the intracellular reutilization of amino acids from protein breakdown in both the fasted and fed states (1,2,28–30). The net result would be that amino acid release from the intramuscular free pool would be reduced with resistance exercise.”

Since protein intake did not change from habitual intakes, they concluded that novice trainees adding significant lean mass do not require additional protein beyond habitual intakes.  They also surmised that since advanced trainees gain lean mass at a much slower rate, or not at all, the protein requirement of an advanced trainee is probably even lower than that of a novice.

In their words:

“Although our data do not directly address the level of protein intake at which zero nitrogen balance would occur, the significantly more positive nitrogen balance after training demonstrates a more efficient utilization of dietary protein in the trained state.”

Commentary

Moore et al report a very rapid rate of lean mass accrual.  If maintained for 50 weeks in a row, an individual would gain 25 pounds of lean mass.  A subject starting at 150 pounds would end the year weighing 175 pounds, a huge transformation. 

These results suggest that the actual protein requirement for a novice trainee adding 0.25 kg (0.5 pound) lean mass per week lies somewhere below 1.4 g/kg/d.  

How far below? 

Castaneda et al investigated the effect of 12 weeks of resistance training on muscle mass accrual in older adults (average age of 65 years) with chronic kidney disease. [2]   These people consumed a diet providing only 0.6 g protein/kg bodyweight/d, less than half the amount consumed by the subjects of the Moore et al study.  

After 12 weeks of strength training, the subjects showed substantial decreases in markers of inflammation (C-reactive protein and interleukin-6) and substantial increases in strength (about 28%) and muscle hypertrophy (about 23% increase in muscle fiber cross-sectional area).  Considering that these subjects were about 3 times the age of the subjects in the Moore et al study (65 vs. 22 years) and suffering from chronic kidney disease, this 23% increase in muscle cross-sectional area compares very well with the 50% increase found in the Moore et al study.

This study indicates that humans can gain muscle mass on protein intakes as low as 0.6 g/kg/d, which interestingly roughly corresponds to the estimated median protein requirement of 0.65 g/kg/d. [3] 

Human muscle consists of ~70% water, ~30% protein by weight.  The Moore et al subjects added ~33 g of lean mass daily, equating to adding ~10 g of protein to their musculature daily. 

The Moore et al subjects averaged 62 kg of lean mass at the start of the study and 65 kg at the end. [4] 

Using the estimated protein requirement of 0.83 g/kg/d [3], ninety-eight percent of individuals starting this program at 62 kg (136 lb) of lean mass would require not more than 50 g of protein per day.  After gaining 2.8 kg (6 pounds) of lean mass, the individual would have 65 kg (143 lb) of lean mass and a protein requirement of not more than 52 g per day.  During the training period, he would require an additional 10 g of protein per day (to accrue 33 g of lean mass daily).  Thus, from start to end, I would estimate his protein requirement as no higher than 60-62 g per day. 

Using the median protein requirement of 0.65 g/kg/d, possibly fifty percent of individuals in the Moore study would require no more than 50 g of protein per day to achieve the results reported.

Since Moore et al report the habitual and controlled protein intake of these subjects as falling between 109 and 125 g per day, by my calculations, the people in this study may have consumed 40 to 60 g excess protein every day, beyond the requirement for building 6 pounds of lean mass in 12 weeks.

According to Moore et al, their 12 subjects required and consumed about 3000 kcal per day. Sixty-two grams of protein provides 248 kcal, which constitutes eight percent of total energy intake.  It would seem possible then that adult physically active humans are adapted to food sources that provide about 8 percent of calories as protein, assuming carbohydrate requirements are met directly rather than through gluconeogenesis.

The following table provides the percent of calories supplied as protein in various foods:

 

From this it appears that many plant foods, like potatoes, could provide plenty of protein for supporting health and muscle growth if eaten in quantities adequate to cover caloric requirements.

From an evolutionary standpoint, the Moore et al findings make more sense than the idea that strength training increases protein requirements.   

As a general rule,  organisms adapt to demands by resisting the damage those demands inflict.  For example, using your hands for labor will result in callus formation.  Calluses are more resistant to damage than soft skin.  Tanned skin is more resistant to sun damage than pale skin.  Thus, we should expect that the body would respond to heavy physical activity by becoming more resistant to muscle protein degradation and reducing the protein requirements of muscle tissue.

Natural selection would have favored those humans that were most efficient at using available resources. Those who had tremendously increased protein requirements as a result of physical activity would have had to expend more energy on the food quest than those who became more efficient at using protein and deriving protein from less energy expensive resources (i.e. plants vs. animals). Those forced to spend more energy on the food quest would have had less energy left for reproduction; hence they would have left fewer descendants.    

Survival of the most efficient.

Zone Out

Neil Mann belongs to the team of researchers who work with Loren Cordain and promote high intakes of lean meat on an evolutionary basis.

For example, he authored Dietary lean red meat and human evolution in which he argues that various lines of study "indicate the reliance on meat intake as a major energy source by pre-agricultural humans."

Mann and another team from Royal Melbourne Institute of Technology published a new study of the efficacy of a high (30%) protein diet, in comparison to a high (55%) carbohydrate diet, for type 2 diabetes.

The effect of high-protein, low-carbohydrate diets in the treatment of type 2 diabetes: a 12 month randomised controlled trial.

In this study, 99 subjects received advice to follow low-fat (30% total energy) diets; 53 of those received instructions to eat a diet supplying 30% of total energy from protein and 40% from carbohydrate (high protein arm), while  46 received instructions to eat a diet supplying 55% of total energy from carbohydrate and 15% from protein.   

The high-protein diet had the same proportions of protein, fat, and carbohydrate (30:30:40) recommended by Barry Sears in his "Zone" diet books.  Supposedly this proportion produces better blood sugar and insulin control than a high carbohydrate, lower protein diet.

The aim was to find out if eating a diet high in protein would provide superior glycemic control to a diet high in carbohydrate, so the primary endpoint was change in HbA(1c).  "Secondary endpoints included changes in weight, lipids, blood pressure, renal function and calcium loss."

The results?

"HbA(1c) decreased in both groups over time, with no significant difference between groups (mean difference of the change at 12 months; 0.04 [95% CI -0.37, 0.46]; p = 0.44). Both groups also demonstrated decreases over time in weight, serum triacylglycerol and total cholesterol, and increases in HDL-cholesterol. No differences in blood pressure, renal function or calcium loss were seen."

Mann et al concluded:

"These results suggest that there is no superior long-term metabolic benefit of a high-protein diet over a high-carbohydrate in the management of type 2 diabetes."

I don't have access to the full text, but since the team that did this study includes Neil Mann, one of the strongest proponents of the idea that humans are adapted to diets high in animal protein, who might have a bias in favor of high-protein diets, this study appears to undermine the high-protein approach to diabetes.

It doesn't appear to do the Zone Diet any favors either. 

On the other hand, it supports the already established body of literature showing efficacy of a high-carbohydrate approach to diabetes type 2.   The high-carbohydrate diet apparently produced meaningful decreases in weight, HbA(1c), triglycerides, and total cholesterol, and increases in HDL.

The decrease in trigs and elevation of HDL are particularly of interest, since very often I see claims that high carb diets raise trigs and lower HDL. 


This study provides evidence against the claim that humans are specially, evolutionarily adapted to high-protein diets and maladapted to high-carbohydrate diets, and undermines the claim that this one disease of civilization, type 2 diabetes, and its chief feature, hyperinsulinemia, arise from high-carbohydrate diets. 

Of interest, both diets had relatively low fat contents.  Since altering the ratio of protein and carbohydrate appeared to have no effect on results, this study may also suggest that reduction of dietary fat proportion plays a key role in the treatment of type 2 diabetes if the goals are reduction of body mass, HbA(1c), triglycerides, and total cholesterol, along with increases of HDL.

Catching Fire

Catching Fire by Richard Wrangham presents a compelling argument that the primary nutritional change driving human evolution from small-brained Homo habilis to large-brained Homo sapiens was cooking––not meat-eating.

Wrangham starts off with some critical observations:  No known human tribe lives on a predominantly raw food diet, and those modern people who attempt to live on a largely raw food diet have demonstrated difficulties maintaining body mass, energy levels, and fertility.  This points to the hypothesis that modern humans are actually "adapted to eating cooked food in the same essential way as cows are adapted to eating grass, or fleas to sucking blood, or any other animal to its signature diet.  We are tied to our adapted diet of cooked food, and the results pervade our lives, from our bodies to our minds.  We humans are the cooking apes, the creatures of the flame."

Traditional Chinese medicine has for milennia maintained that humans need to eat cooked food to get adequate food energy (Pinyin: gu qi).  In The Tao of Healthy Eating, traditional Chinese physician Bob Flaws writes:

"Traditional Chinese medicine suggests that most people, most of the time, should eat mostly cooked food.  Cooking is predigestion on the outside of the body to make food more easily digestible on the inside.  By cooking foods in a pot on the outside of the body, one can initiate and facilitate the stomach's rottening and ripening in its pot on the inside of the body.  cold and raw foods require that much more energy to transform them into warm soup within the pot of the stomach.  Since it takes energy or qi to create this warmth and transformation, the net profit from this transformation is less.  Whereas, if one eats cooked foods, less qi is spent in the process of digestion.  This means that the net profit of digestion, i.e. qi or energy, is greater."

This perspective contradicts the common belief that raw food is better than cooked because cooking can destroy nutrients.  But as Flaws points out,  net nutrient delivery matters more than gross amount of nutrient in the raw food.  Let's assume that a carrot has 10 units of X nutrient, but only 10% of it is available to humans because it is locked in an largely indigestible cellulose envelope.  Let's say that cooking destroys 50% of that nutrient (a gross overestimation for proper cooking), but increases the availability to 50%.  The net delivery of X from the raw carrot is 1 unit, but the net from the cooked carrot is 2.5 units. 


Wrangham presents multiple lines of evidence that humans and non-humans have a greater net macronutrient absorption from cooked than from raw foods, resulting in cooked foods delivering more energy than raw foods.

Wrangham includes some of the research I discussed in my series on raw vegan diet, which found that a high proportion of people eating diets high in raw foods (70% or more raw) are underweight and have low fertility.   Belgian researchers showed that humans can digest only about 65% of the protein in raw eggs, but 91-94% of the protein from cooked eggs. [1] Another team showed that enzymatic  digestion of heated beef protein increased by four times over raw beef protein. [2] This occurs because cooking denatures protein more effectively than stomach acid, making it more vulnerable to enzymatic digestion.

Wrangham's hypothesis competes with the Man-The-Hunter hypothesis which maintains that humans evolved big brains and small guts by route of increased meat-eating.   However, Wrangham points out that the hunting hypothesis can't account for some of the facts. Increased meat-eating might explain the transition from Australopithecines to Homo habilis (habilines), but not the transition from the habilines to Homo erectus:

"Meat-eating accounts smoothly for the first transition, jump-starting evolution toward humans by shifting chimpanzeelike australopithecines into knife-wielding, bigger-brained habilines, while still leaving them with apelike bodies capable of collecting and digesting [raw] vegetable foods as efficiently as did australopithecines.  But if meat eating explains the origin of the habilines, it leaves the second transition unexplained, from habilines to Homo erectus.  Did habilines and Homo erectus obtain their meat in such different ways that they evolved different kinds of anatomy?  Some people think the habilines might have been primarily scavengers while Homo erectus were more proficient hunters.  The idea is plausible, though archaeological data do not directly test it.  But it does not solve a key problem concerning the anatomy of Homo erectus, which had small jaws and small teeth that were poorly adapted for eating the tough raw meat of game animals.  These weaker mouths cannot be explained by Home erectus's becoming better at hunting.  Something else must have been going on."

Increased meat eating can't explain whey we have such small mouths and jaws. 

"Given that the mouth is the entry to the gut, humans have an astonishingly tiny opening for such a large species....To find a primate with as relatively small an aperture as that of humans, you have to go to a diminutive species, such as a squirrel monkey weighing less than 1.4 kilograms (3 pounds). In addition to having a small gape, our mouths have a relatively small volume––about the same size as chimpanzee mouths, even though we weigh some 50 percent more than they do.  Zoologists often try to capture the essence of our species with such phrases as the naked, bipedal, or big-brained ape.  They could equally well call us the small-mouthed ape."

Compare the jaws of any raw food eating animal to human jaws.  The largely vegetarian chimp has a gape much larger than that of a human:

Source:  Junglewalk

The carnivorous cat has a gape nearly half the size of its head, and the jaws are very powerful for cutting through raw meat. 

You can see some other big yawns here.  Compare to the modern human gape:

Source:  Flikr

Humans have a small mouth for such a large head.  The larger gape of other species is not for taking in large bites, it is necessary for leverage to crush tough, chewy raw foods. 

By the way, although Wrangham does not mention it, the shrinkage and reorganization of the mouth laid the foundation for speech.  Thus, we may owe our linguistic abilities to the mastery of fire and cooking.  I seem to recall reading that another anthropologist had proposed this hypothesis more than 20 years ago, but I no longer have the book that had the reference.

If evolution from Homo habilis to Homo erectus had been driven by increased consumption of raw meat, with technology and cooking as an afterthought, we would expect to have seen it maintain the large powerful ape mouth and jaws, retained the large, sturdy teeth, and increased the shearing action for adaptation to meat eating.  Instead, from the habilines to the erectines the mouth and teeth shrank.

Here's a habiline skull:

Source: www.anhb.uwa.edu.au/.../ skulls/s10_homo_habilis

And here's an erectine skull:

Source: www.ma.krakow.pl

The erectine jaw and teeth are much smaller relative to body size.  Erectines had a smaller gape and must have had a softer diet than the habilines.  The skeletal remains provide the best available evidence that some tribe of Homo habilis discovered something that made for a much softer and energy-rich diet, giving rise to Homo erectus. 

One might think that the use of knives and hammers alone selected for smaller mouths.  Perhaps habilines simply cut the meat into small pieces or pounded it tender.  Although initially plausible, on further examination, this loses credibility, because it can't explain how an animal adapted to a diet consisting predominantly of raw vegetation can continue eating that vegetation while adapting to the raw meat portion of the diet.

Wrangham notes that "Peter Lucas has calculated that the size of a tooth needed to make a crack in a cooked potato is 56 percent to 82 percent smaller than needed for a raw potato."  Thus, so long as human ancestors continued to eat raw plants, they needed large teeth and jaws.  And they definitely needed to eat plants.

"The problem is that tropical hunter-gatherers have to eat at least half of their diet in the form of plants, and the kinds of plant foods our hunter-gatherer ancestors would have relied on are not easily digested raw.

Tropical wild game simply does not provide adequate amounts of fat or carbohydrate to prevent excessive intake of protein resulting in ammonia and urea accumulation, especially in the annual dry seasons, when the whole carcass fat levels of game will drop as low as 1 percent to 2 percent.
 
By the way, Wrangham notes:

"Starchy foods make up more than half of the diets of tropical hunter-gatherers today and may well have been eaten in similar quantity by our human and pre-human ancestors in the African savannas."

Moreover, if raw meat was a staple of our ancestors, we would expect modern humans to have some significant resistance to toxins produced by bacteria that infect raw meat.  But we are still vulnerable to those bacterial toxins.

In addition, there is a major economic problem with the meat-eating hypothesis.  Wrangham has studied chimps directly, watching them hunt and eat.  The typical chimp has to spend about 6 hours daily chewing its bulky, chewy raw foods.  They hunt opportunistically, but will only spend 15 to 20 minutes on a hunt.  If not successful in that time frame, they give up and return to eating plants.  Why?

Wrangham explains that because digestion of raw food takes more time than digestion of cooked food and costs a lot of energy, a chimp has to devote eight or nine hours daily to feeding in order to get adequate energy.  Australopithecines and habilines probably had similar constraints.  This would have prevented them from investing much time in hunting:

"Males who did not cook would not have been able to rely on hunting to feed themselves.  Like chimps, they could hunt in opportunistic spurts.   But if they devoted many hours to hunting, the risk of failure to obtain prey could not be compensated rapidly enough.  Eating their daily required calories in the form of their staple plant foods would have taken too long."

As Wrangham explains, a division of labor into hunting and gathering would not solve this problem, so long as the food was consumed raw.

"Suppose that a hunter living on raw food has a mate who is willing to feed him, that his mate could collect enough raw foods for him (while satisfying her own needs) and would bring them back to a central place, to be met by her grateful mate.  Then suppose the male has had an unsuccessful day of hunting....The hungry hunter needs to consume, say, two thousand calories, but he cannot eat after dark.  To do so would be too dangerous, scrabbling in the predator-filled night to feel for the nuts, leaves, or roots his gatherer friend brought him.  If the hunter slept on the ground, he would be exposed to predators and large ungulates as he fumbled for his food.  If he were in a tree, he would find it hard to have his raw foods with him because they do not come in tidy packages.  

"So to eat his fill he would have to do most of his eating before dusk, which falls between about 6 and 7 P.M. in equatorial regions.  If he had eaten nothing while on the hunt, he would need to be back in camp before midday, and there he would find his mate's gathered foods 9assuming she had been able to complete her food gathering so early in the day).  He would then have to spend the rest of the day eating, resting, eating, resting, and eating.  In short, the long hours of chewing necessitated by a raw diet would have sharply reduced hunting time.  It is questionable whether the sexual division of labor would have been possible at all.

"The use of fire solved the problem.  It freed hunters from previous time constraints by reducing the time spent chewing.  It also allowed eating after dark.  The first of our ancestral line to cook their food would have gained several hours of daytime. Instead of being an opportunistic activity, hunting could have become a more dedicated pursuit with a higher potential for success.  Nowadays men can hunt until nightfall and still eat a large meal in camp.  After cooking began, therefore, hunting could contribute to the full development of the family household, reliant as it is on a predictable economic exchange between women and men."

 In short, cooking (and other culinary technologies that make food softer and easier to digest) made it possible for humans to pursue increased meat-eating.  It freed men from the need to continuously feed on plant foods, giving them time to devote to hunting meat. 

Simply put, cooked food delivers more energy and nutrition in a smaller, more easily digested package than raw food.  Wrangham argues that since Homo erectus had a larger brain and a much smaller face, mouth and teeth than Homo habilis, probably some tribe of Homo habilis first controlled fire and used it for cooking.  The resulting increase in energy and nutrient availability led to rapid selection for smaller guts and larger brains and bodies.  By providing protection from nocturnal predators, control of fire also enabled human ancestors to give up tree-dwelling.  It also supported the sexual division of labor (hunting and gathering/cooking) present in human cultures.

Wrangham's Catching Fire will provide plenty of food for thought for anyone interested in ancestral nutrition. 

Stoned On Fat?

Neuroscience researchers at UC Irvine, , led by Daniel Piomelli, have just announced results of a study done on rats, in which they found that ingestion of fatty foods stimulates the release of endocannibinoids, chemicals that activate the same receptors affected by THC.  According to the UC Irvine news release:

"The process starts on the tongue, where fats in food generate a signal that travels first to the brain and then through a nerve bundle called the vagus to the intestines. There, the signal stimulates the production of endocannabinoids, which initiates a surge in cell signaling that prompts the wanton intake of fatty foods, Piomelli said, probably by initiating the release of digestive chemicals linked to hunger and satiety that compel us to eat more."

In other words, rats eating fats had the munchies.  Feeding rats carbohydrate or protein did not have this effect.  Piomelli offers an evolutionary explanation:

"Piomelli said that from an evolutionary standpoint, there’s a compelling need for animals to consume fats, which are scarce in nature but crucial for proper cell functioning. In contemporary human society, however, fats are readily available, and the innate drive to eat fatty foods leads to obesity, diabetes and cancer."

The study results will appear this week in the online edition of Proceedings of the National Academy of Sciences. 

This finding dovetails with the reward theory of overeating, suggesting that animals including humans get more immediate endogenous drug-like reward from eating fats than carbohydrates or proteins, partially because fats supply more than twice as much energy per gram as carbohydrate or protein.

Piomelli apparently also serves as Director of the UCI School of Medicine’s Center for Drug Discovery & Development and hopes to find a pharmaceutical solution:

"The findings suggest it might be possible to curb this tendency by obstructing endocannabinoid activity – for example, by using drugs that “clog” cannabinoid receptors. Since these drugs wouldn’t need to enter the brain, they shouldn’t cause the central side effects — anxiety and depression — seen when endocannabinoid signaling is blocked in the brain, Piomelli noted."

So there you go, a pharmaceutical solution to the obesity problem.   Just throw a monkey wrench into the intricate and poorly understood symphony of neurochemicals.  No need to worry about side-effects, right?

How about teaching people to recreate the ancestral environment instead?  What did he say?  "Fats are scarce in nature."  By "nature" he means in the ancestral environment. 

Could this be why humans need only about 20-25 g of essential fats daily, compared to ~50-60 g of protein and at least 150 g of glucose?  Does it make sense that human macronutrient requirements would mirror the relative availability of nutrients in the ancestral environment and diet?

And are things really that different in the agricultural food supply?  I mean, although fat seems abundant in industrialized nations, does this reflect nature, or human intervention?  After all, agriculture is part of nature.  Does agriculture produce more fats, proteins, or carbohydrates?  If you look at the world at large, at the entire human food supply on the planet, is fat relatively abundant, or relatively scarce, although concentrated in certain locations?  How about protein?  Carbohydrate?

Why would evolution favor a system that offers an animal a higher immediate reward for eating fats than for eating protein or carbohydrate? 

Would this reward system be more advantageous in an environment where fats were easy to obtain, or in an environment where fats were hard to obtain?

In other words, would nature make it more highly rewarding to eat something available frequently, with little effort, or something available only infrequently and with great effort?

From another angle, which would this system help most:  an animal that had a continuous supply of fats, or one that had an intermittent supply of fats?

Effect of dietary fat on satiation within and between meals

Blundell et al performed a series of four experiments to determine the effect of fat content of a meal on satiety, both during and after meals. [1 full text ]

The first  experiment involved giving 16 lean, healthy subjects a standard breakfast of 440 kcal, or the same breakfast supplemented with either fat or carbohydrate calculated to provide ~360 kcal.  The standard breakfast consisted of orange juice, scones, and fruit yogurt.  The supplements consisted of either polyunsaturated margarine and cream, or a combination of sucrose, maltodextrin, and glucose.  The following table provides the data on the three types of breakfasts:

Each individual tested each breakfast with a one week interval between tests.  The subjects rated the palatability of the meals, and rated hunger, desire to eat, fullness, and prospective consumption before the breakfasts and periodically during the rest of the day.

After the breakfasts, the subjects ate measured meals, provided by the experimenters, for lunch and dinner on the same day, and kept weighed food records for the period between dinner that day and breakfast the next.

In this experiment, neither the high fat nor the high carbohydrate breakfasts appeared to exert any significant effect on intakes of macronutrients at the subsequent lunch or dinner.  However, subjective reports of hunger did differ between the high carbohydrate and high fat meals.   Specifically, the subjects reported less hunger with the carbohydrate-supplemented meal compared to the baseline or fat-supplemented breakfasts.  The following figure depicts the effects:

When the subjects ate the carbohydrate-enriched breakfast, they experienced less post-meal hunger than when given the fat-enriched breakfast, indicating that they found fat less satisfying than carbohydrate during the post-ingestive phase. 

In the second experiment, 12 lean healthy individuals consumed the same breakfasts given in experiment one, followed by a snack provided 90 minutes after the breakfasts.  Subjects rated themselves as less hungry and more full after the carbohydrate-enriched breakfasts, compared to the fat-enriched breakfasts.   They also ate smaller snacks at the 90 minute mark when they had the carbohydrate-enriched breakfast, compared to when they ate the fat-enriched breakfast.  The following figure depicts the effects:

In the third experiment, 16 lean healthy subjects consumed the same breakfasts as in experiment one, followed by a snack 90 minutes after the breakfast, or a meal 270 minutes after the breakfast.   The following table depicts the results:

When given the carbohydrate-enriched breakfast, the subjects  voluntarily ate a smaller snack at 90 minutes after, compared to what they ate after the fat-enriched breakfast.  Of interest, although the fat-enriched breakfast supplied ~800 kcal, 90 minutes after that breakfast they voluntarily consumed a snack the same size as they had 90 minutes after the 440 kcal baseline breakfast.  This means that at 90 minutes after the breakfast, the 800 kcal breakfast providing 57% energy from fat was no more satisfying than the 440 kcal breakfast providing only 10% energy from fat.  

The greater satiating effect of the high carbohydrate breakfast disappeared at 270 minutes.  Blundell et al attributed the greater satiating effect of the carbohydrate-supplemented breakfast at 90 minutes to the greater elevation of blood glucose achieved by the carbohydrate-rich breakfast.  As the glucose was oxidized or stored over the next 180 minutes, this satiating power declined.

In the fourth experiment, 12 obese women ate either one of two lunches, each on two different occasions.  One lunch supplied 527 kcal, the other supplied 985 kcal.  Between lunch and dinner, the subjects rated their hunger at one hour intervals.  At dinner, each woman was offered either foods supplying 50% of energy as fat, or 50% of energy as carbohydrate and allowed to eat as much as desired.  So, each woman had four different procedures:

1.  A 527 kcal lunch, followed by an ad libitum high-fat, low-carbohydrate (50% energy as fat) meal for dinner.

2.  A 527 kcal lunch, followed by an ad libitum low-fat, high-carbohydrate (50% energy as carbohydrate) meal for dinner.

3.  A 985 kcal lunch, followed by an ad libitum high-fat, low-carbohydrate (50% energy as fat) meal for dinner.

4. A 985 kcal lunch, followed by an ad libitum low-fat, high-carbohydrate (50% energy as carbohydrate) meal for dinner.

Not surprisingly, the size of the mid-day meal determined the course of subjective hunger during the afternoon, i.e. the smaller meal was followed by earlier return and greater intensity of hunger as depicted in the following figure:

However, the size of the midday meal did not affect the energy content of the ad libitum dinner meal as much as the relative fat and carbohydrate contents of the offered dinners.  The following table displays the impact of midday meal size and dinner composition on satiation during the dinner meal:

Regardless of whether given the high-energy or low-energy midday meal, the subjects consumed an average of 5.6 MJ/1336 kcal for dinner when given high-fat foods, but only 2.8MJ/677 kcal when given the high-carbohydrate/low-fat foods.  This demonstrated that within a meal, high-carbohydrate foods appear to have a greater satiating effect, i.e. subjects voluntarily consumed less food energy when given a high-carbohydrate selection compared to when given a high-fat selection.

Since the high-fat meal was at least 50% energy from fat, and the average intake was 1336 kcal, this means the average intake of non-fat nutrients at the high-fat meals was at most 668 kcal, approximately the same as the 677 kcal the women consumed when eating the low-fat high-carbohydrate meals. It appears as if the women were eating to achieve a certain intake of non-fat nutrients (carbohydrate or protein), regardless of the fat content of the food.  Since the high-carbohydrate meals supplied more carbohydrate and protein per ingested gram of food, the apparent carbohydrate or protein drive was satisfied with less total fat and energy intake.

The researchers followed the food intake of these women after dinner and throughout the next day as well.  Some would predict that the high fat intake of the high-fat meal would reduce post-meal and next-day food intake.  That did not happen.

 The women consumed after-dinner snacks averaging 310 kcal after the high-fat meal, and 391 kcal after the low-fat, high-carbohydrate meal.   The 81 kcal lower energy intake is insignificant compared to the nearly 700 kcal greater kcal intake at the preceding high- meal. 

The day after having the high-fat dinner, the women consumed an average of 1800 kcal, whereas the day after having the low-fat dinner, the women consumed an average of 1556 kcal.  This ~250 kcal difference did not reach statistical significance, but the direction was opposite of the prediction that they would compensate for the high-energy intake of the previous day by reducing energy intake in subsequent days.  It may even suggest that the high-carbohydrate dinner had a satiating effect that lasted into the next day. 

Now, looking at this from an evolutionary perspective:  If humans find carbohydrate more satisfying than fat, this suggests that evolutionary diets were high in carbohydrate and low in fat.  An organism geared to consuming fat would get the most satisfaction from fat.  An organism geared to consuming carbohydrate would continue eating until it either satisfied its carbohydrate requirement, or reached the limit of  its ability to convert protein or glycerol to carbohydrate, whichever comes first, regardless of “energy” intake--exactly as seen in these women. 

Since the brain regulates eating behavior and it primarily relies on glucose as its main fuel, we can reasonably expect that the brain has a carbohydrate drive, meaning that it drives people to eat until they ingest adequate glucose, or enough protein to provide the brain with adequate glucose.   

In other words, I would predict that, barring interference from the conscious mind (i.e. so-called "discipline") attempting to control macronutrient ingestion,  hungry people will keep eating until they at least minimally satisfy their carbohydrate requirements either directly from dietary carbohydrate, or indirectly from dietary protein, or until in the latter case they reach the limit the body imposes on protein ingestion, whichever comes first, regardless of total fat (or energy) intake.

Several studies appear to indicate that primitive Eskimo diets aligned with this prediction.  Several studies have indicated that Eskimos consume  very high percentage of energy as protein [Table from 2 full text ]:

On average these studies suggest that free living Eskimos derive 48% of energy from protein.  Assuming a 3000 kcal diet for an active male, this would be 1440 kcal/360 g of protein daily.  Since the human protein (70 kg reference man) requirement ranges from 50 to 75 g per day under most circumstances, these data indicate that the Eskimo may consume ~300 g excess protein daily.  According to Jungas et al, about 58% of catabolized protein will appear in the blood stream as glucose [3 ] .  Therefore, an Eskimo consuming about 300 g excess protein daily will generate from this about 174 g glucose, approximately the minimal amount required by the central nervous system. 

Some have criticized the data in the table above claiming that Eskimos eat ~80% of kcalories as fat based on claims made by Stefansson.  I find it extremely unlikely that four separate investigations produced incorrect data on Eskimo macronutrient consumption, and since Stefansson did not directly measure the macronutrient intake of Eskimos, I see no reason we should accept his estimate as more accurate.

The idea that Eskimos couldn’t have eaten a diet providing 48% of energy as protein is based on the claim that a protein intake of this magnitude will lead to so-called “rabbit starvation” from excess protein intake.  About “rabbit starvation” Cordain et al [4 ] have written:

“Excess consumption of dietary protein from the lean meats of wild animals leads to a condition referred to by early American explorers as “rabbit starvation,” which initially results in nausea, then diarrhea, and then death (39). Clinical documentation of this syndrome is virtually nonexistent, except for a single case study (42). Despite the paucity of clinical data, it is quite likely that the symptoms of rabbit starvation result primarily from the finite ability of the liver to up-regulate enzymes necessary for urea synthesis in the face of increasing dietary protein intake.” [Emphasis added]

Aside from the fact that clinical documentation of “rabbit starvation” is “virtually nonexistent,” Shaefer reported that primitive Eskimos on native diets had enlarged livers in comparison to Caucasians, and when they reduced protein intake, substituting carbohydrate, their livers reduced in size [5, full reference below].  This may suggest that Eskimos on native diets had livers adapted to chronically very high protein intakes via hypertrophy, whereas explorers (including Stefansson) may have experienced acute “rabbit starvation” when forced to eat very lean meat because unlike Eskimos they did not have previous lifelong exposure and hepatic adaptation to very high protein intakes.  

A Word About Protein And Satiety

A number of studies have shown that when given energy-restricted diets, people find higher protein intakes more satiating (within meals) and satisfying  (between meals) than lower protein diets.  For a while I felt impressed by this, thinking that protein is more satiating than any other nutrient. 

However, I now think this finding simply reflects the long-known fact that when when we restrict total food energy intake, and therefore carbohydrate intake, protein requirements increase, because carbohydrate restriction increases the use of lean mass to produce glucose.  Thus, under hypocaloric conditions, a drive to meet increased protein requirements--what we might call "protein hunger"-- may surface. 

Again, it has been known for a long time that protein requirements increase under hypocaloric conditions, so these recent studies showing higher protein diets to be more satiating under hypocaloric conditions appear to me to just be late application of something we have known for decades.  These findings do not mean that protein is the most satiating nutrient under all conditions.  I performed a quick PubMed search for studies of the satiating effects of protein under ad libitum conditions, and found only one study  [6 abstract ] which reported both "higher protein led to greater daily fullness" and "Protein quantity did not influence daily hunger, glucose, or insulin concentrations," i.e. inconsistent effects.


Given what we know about the satiating power of carbohydrate and protein, and fat balance versus energy balance, Astrup suggests that the optimal diet for reducing body fat might be very low in fat, high in carbohydrate, and moderately high in protein, for example 60-65/20-25/15 carbohydrate/protein/fat [7 abstract, 8 full text].

Take Home

1)  This series of clinical studies found that both lean and obese people not invested in consciously controlling their macronutrient intakes experienced most satisfaction and less hunger from high-carbohydrate than from high-fat meals.

2) The biological basis for this probably lies in the brain's demand for glucose.  The brain drives eating behavior, and since it prefers glucose to other fuels, it has a drive to satisfy its own requirement for glucose.

3)  Barring conscious control of macronutrient intake/ratios, a majority of people probably will eat to achieve an adequate intake of carbohydrate, either by consuming carbohydrate directly, or by consuming enough protein to produce adequate carbohydrate, continuing to eat until either they satisfy their carbohydrate drive, or they meet the limit of the body's ability to convert protein to carbohydrate, whichever comes first, and regardless of total energy intake. 

4) If people choose high-fat foods to satisfy carbohydrate requirements, they will very likely consume more fat (grams) than they can burn in a day, leading to progressive gain of fat weight.

Notes:

5. Schaefer O. Eskimos (Inuit). In: Burkitt DP, Trowell HC, eds. Western Diseases: Their Emergence and Prevention. Cambridge, MA:  Harvard University Press, 1981:114.