Intermittent Fasting Good, But Don't Do It Yet? The Expert Double-Bind Strikes Again

Science Daily saw fit to reprint a EurekAlert announcing that a "Study finds routine periodic fasting is good for your health, and your heart."  The article describes research done by a team apparently led by Dr. Benjamin Horne, PhD, MPH.  The team had some people fast for 24 hours and recorded the changes in the participants blood levels of cholesterol and hormones.  


They found that during the fasting period, blood levels of both LDL and HDL increased.   According to the article, Dr. Horne explains the findings this way:

"Fasting causes hunger or stress. In response, the body releases more cholesterol, allowing it to utilize fat as a source of fuel, instead of glucose. This decreases the number of fat cells in the body," says Dr. Horne. "This is important because the fewer fat cells a body has, the less likely it will experience insulin resistance, or diabetes."

I agree with the first sentence, but I doubt the second.  I know of no way that elevations of blood cholesterol influence cells' fuel use.  If what he says was true,  high serum cholesterol would indicate a metabolism that burns fat in preference to glucose, and raising cholesterol would treat obesity.

Assuming Dr. Horne actually said this, I think he has cause and effect confused.  When fasting, the body releases fat from adipose for use as fuel, and cholesterol gets released from those tissues at the same time.

Dr. Horne, I suggest that you get a copy of Eat Stop Eat by Brad Pilon if you want to learn how fasting works, or at least consult a standard physiology textbook.  ESE has an extensive bibliography referring to dozens of studies of the effects of fasting.  You will find that the textbooks and numerous research papers tell us that fasting lowers insulin, and the reduction of insulin allows the body to use greater amounts of fat as a fuel.

Next he says that this process "decreases the number of fat cells in the body."  Wow!  I have never seen any evidence that any method short of surgical excision (lipectomy) can reduce the number of fat cells in the body.  So far as I know, fasting or dieting can reduce the amount of fat stored in the fat cells we have, but not the number of fat cells.   Dr. Horne,  if you have evidence that fasting can reduce the number of fat cells, I sure would like to see it.

Horne's team also confirmed previous research showing that fasting has profound effects on human growth hormone (HGH) secretion.  Increased HGH protects muscle mass and increases fat metabolism.  Horne's research found that "During the 24-hour fasting periods, HGH increased an average of 1,300 percent in women, and nearly 2,000 percent in men."

So this fasting thing sounds pretty good, eh?  Don't get carried away:

While the results were surprising to researchers, it's not time to start a fasting diet just yet. It will take more studies like these to fully determine the body's reaction to fasting and its effect on human health. Dr. Horne believes that fasting could one day be prescribed as a treatment for preventing diabetes and coronary heart disease.

I suppose they want to cover their bases, but this kind of "disclaimer" gets my goat.  These people seem like hypercautious nannies wanting everyone to stay "safe," as if going without eating for 24 hours was some unprecedented adventure into dangerous, uncharted territory.  My cynical part read it this way:  "Look, this fasting thing could do awesome things for your health, even prevent diabetes or heart disease, but now that you know that, we want you to go back to sleep.  After all, we wouldn't want to discourage the use of drugs...." 

In nature, most carnivores or omnivores spend a lot of time without food.  Without refrigerators and convenience stores, if you want to eat, you have to hunt, and hunting takes time.  As a result, most non-human carnivores spend a far greater portion of their lives in the fasted than the fed state. 

Ethnographic records also indicate that most hunter-gatherer tribes have traditionally eat only one or at most two main meals daily, in late afternoon or early evening, which means that the people fast at least 16 hours and often 20-24 hours almost daily.  We can surmise that our paleolithic ancestors also spent far more time in the fasting than in the fed state.  Thus, rather than having to justify intermittent fasting,  which occurs as a matter of course in natural circumstances, advocates of eating more frequently need to prove the safety of frequent feeding, because it departs from the paleolithic default.

I fast 16-17 hours almost every day of the week and usually have at least one fast lasting at least 20 hours once weekly.  I almost always do my heavy and light training after at least 16 hours of fasting.  I've been doing this for more than two years with only  positive results.  I highly recommend it for weight management and health enhancement.  Don't let the nannies discourage you from doing something absolutely natural. 

Slaying the Fasting Myth at Examiner.com

I just posted an article on intermittent fasting at Examiner.com.

Slaying the Fasting Myth

Intermittent fasting prolongs life in mammals

Although experiments have demonstrated that caloric restriction (CR) can extend lifespan in yeasts, worms, mice, and possibly primates, few people would want to pay the price of caloric restriction to extend life. The Caloric Restriction Society has a page listing the risks of CR, which include

-chronic hunger, cravings, or food obsession
-large loss of body mass, up to 25% below normal
-loss of strength
-low body temperature
-decreased testosterone
-menstrual irregularities
-slower wound healing
-loss of emergency energy reserves

When Ancel Keys did the Minnesota Starvation Study, he restricted young men to 1800 calories daily, 20-40% below average needs -- similar to recommendations for caloric restriction for longevity. His goal was to get the men down to 25% below normal weight -- the CR society also suggests reaching 10-25% below normal weight.

As reported in the Journal of Nutrition, one of the participants in this experiment, Harold Blickenstaff, "recalled the frustration of constantly thinking about food:

I don’t know many other things in my life that I looked forward to being over with any more than this experiment. And it wasn’t so much ... because of the physical discomfort, but because it made food the most important thing in one’s life ... food became the one central and only thing really in one’s life. And life is pretty dull if that’s the only thing. I mean, if you went to a movie, you weren’t particularly interested in the love scenes, but you noticed every time they ate and what they ate. found men depression, and other effects making for many a long life not worth living.

Energy restriction had numerous adverse effects in the Minnesota Study:

"They experienced dizziness, extreme tiredness, muscle soreness, hair loss, reduced coordination, and ringing in their ears. Several were forced to withdraw from their university classes because they simply didn’t have the energy or motivation to attend and concentrate."

The subjects of the Minnesota Starvation Experiment developed all the visible signs of starvation: "sunken faces and bellies, protruding ribs, and edema-swollen legs, ankles, and faces. Other problems such as anemia, neurological deficits, and skin changes became apparent." The men lost interest in sex, and had no functional energy.

Again from the Journal of Nutrition: "The St. Paul Dispatch reported: '... the ... men on the starvation diet have lost so much physically and mentally that their ambition is gone, their will to go forward is gone, and they cannot do heavy work such as farming, mining, forestry, lifting and many other types of work necessary to rebuild war-torn Europe.'"

So, if you choose caloric restriction, you might spend more years breathing, but would you call that living? Do we have a better way?

On the CR (Caloric Restriction) Society International website FAQ page you can find this:

“Are there any other ways of retarding biological aging or extending lifespan besides CR?

None known to science at this time. .. as of this writing, there is no reliable evidence to support the notion that anything besides CR is capable of retarding biological aging or extending maximum lifespan in adult mammals. “

Yet just above this statement, on the same page, you will find this:

Studies have shown that rodents fed all they can eat [emphasis added], but fasted every two, three or four days, also have an increase in longevity, though the increase is not quite as great as that of rodents on the standard kind of CR (when implemented in mature organisms). For some people, this might be an easier way of doing CR since hunger is limited to two or three days a week.

A humane approach to life extension research would look for a method that would not entail all of the harmful side effects listed above. I personally would not want to live a long, cold, depressed, constantly hungry, food-obsessed, neutered life having insufficient strength, muscle mass, or energy for activities I enjoy, and unable to heal wounds at a normal rate.

I think intermittent fasting can give you more life to live while preserving your ability to live it.

IF extends lifespans of Wistar Rats

In 1945, Anton J Carlson and Frederick Hoelzel of the department of physiology at the University of Chicago published “Apparent Prolongation of the Life of Rats by Intermittent Fasting” in the Journal of Nutrition. This paper detailed the results of their studies in which they put adult rats on intermittent fasting schedules of 1 fast day in 2 days, 1 in 3 days, and 1 in 4 days, compared to control animals allowed to eat ad libitum.

In this study, they fed the rats in four groups, three getting one of three different omnivorous diets and one getting a vegetarian diet.

The three omnivorous diets included:
1) A basic diet consisting of 61.5% cooked and dried whole veal (including practically all of the edible parts of calves, excepting excess fat and blood), 31 % corn starch, 2% powdered yeast, 1% cod liver oil, 1.5% inorganic salt mixture and 3% veal bonemeal. This diet provided 35% protein.
2) The basic diet (#1) plus 10% finely ground alfalfa stem meal.
3) The basic diet plus 5% psyllium seed husk and 5% specially prepared kapok fiber.

The one vegetarian diet consisted of 50% whole wheat flour, 10% peanut flour, 7% lima bean flour, 7% wheat gluten flour (containing 80% gluten), 7% corn gluten meal, 7% linseed meal, 5% powdered yeast, 5% alfalfa leaf meal and 2% NaCl. This diet provided approximately 30% proteins.

Hoelzel had previously performed a study in which he found that rats fasted every other day and fed a diet low in protein on non-fast days developed peptic ulcers within about 2 weeks, but rats fed adequate protein did not develop ulcers.

All groups got lettuce trimmings daily. During feeding periods, they supplied food continuously to all groups, so rats ate ad libitum when not fasting. Fasting began at 42 days (before which all rats received identical feed) and continued until the rats died.

Table 1 of the paper shows the effects on lifespan of fasting 1 day in 2, 3, or 4 days in male and female rats.



Fasting increased the average lifespan of males by 90 days, and that of females by 23 days.

Optimum fasting interval

Upon detailed analysis of their data, Carlson and Hoelzel found that rats fasting 1 day in 4 and 1 day in 2 displayed complications by “extraneous factors” more than either control rats eating ad libitum or rats fasting 1 day in 3. Those factors included:

1) The earliest male and female deaths occurred in the groups fasted 1 day in 4, and it appeared that other rats did not fare as well fasting 1 day in 4 as in 1 day in 3. Carlson and Hoelzel suggested that “Perhaps the amount of food consumed in 3 days of feeding, with increased voracity but without proportionately increased capacity after 1 day of fasting, constituted a greater physiological overstrain than the amount of food consumed by the controls or by the rats fasted 1 day in 3.”
2) Fasting 1 day in 2 produced both a greater mortality rate and the longest-lived rats. The males and females fasted 1 day in 2 also began dying earlier than the rats fasted 1 day in 3. Carlson and Hoelzel commented: “Evidently fasting 1 day in 2 and beginning this at the age of 42 days was too much fasting for some rats. One of the females fasted 1 day in 2 apparently died of a hemorrhage from a chronic duodenal ulcer.” Fasting 1 day in 2 produced the longest-lived male and female rats, 1052 and 1073 days respectively, but the average rat did very poorly on this level of fasting.

Carlson and Hoelzel concluded that the optimum amount of fasting for the average rat in their study was 1 day in 3, or about twice weekly. This fasting frequency produced a 15% increase of average lifespan for females and 20% for males.

Of interest, in their raw data (Table 1), the average lifespan of male rats fasted 1 day in 4 did not significantly differ from those fasted 1 day in 3. Females fasted 1 day in 3 actually on average lived longer than those fasted 1 day in 2, but the reverse for males.

Another way to interpret this: Fasting 1 day in 2 produced a restriction of calories that proved too harmful for the majority of rats. Fasting 1 day in 3 or 4 produced the optimum result without daily caloric restriction.

Taking the average lifespan of 75 years in the U.S., this would mean IF twice weekly could increase the span to 86 to 90.

IF did not affect growth

Whereas 40% CR adversely affects muscle growth and mass, in this study, Carlson and Hoelzel found no or only small effects on growth or body mass in rats fasted 1 day in 4 or 1 day in 3.

Under unrestricted feeding conditions, male Wistar rats reach 450-520 g, and females reach 250-300 g.

In this study Carlson and Hoelzel compared littermates fed ad libitum to those fasted 1 day in 2, 3, or 4 days.

Using litter mate controls, male rats fasted 1 day in 4 attained body mass 91% of males fed ad libitum (413 v. 449 g), those fasted 1 day in 3 attained 85% of the mass of ad libitum males (339 v 397 g), and males fasted 1 day in 2 attained 74% of the body mass of ad libitum littermates (265 v. 356 g).

Female rats fasted 1 day in 4 attained body mass 89% of ad libitum females, those fasted 1 day in 3 attained 89% of ad libitum females, and those fasted 1 day in 2 attained body mass 85% of ad libitum females.

Again using litter mate controls, in some cases fasted rats actually had longer femurs than rats fed ad libitum, illustrating that intermittent fasting did not impair healthy tissue growth. In contrast, as stated by the CR Society's Risks Page, "Physical growth may be impaired by calorie restriction, as observed in lab animals."

Genetic controls

Carlson and Hoelzel found a large variation in response to fasting and feeding regimens. All rats were Wistar variety, and regardless of regime, 67% of all rats died between ages of 550 and 850 days, and 85% between 400 and 900 days. Further, “Some littermate rats, after having been kept from 400 to 1000 days on widely differing nutritional regimens, died within 24 hours or a few days of one another. Four of the twelve rats that lived to be over 1000 days old belonged to one of the seventeen litters.” Thus, genetic factors played a strong role in mortality.

IF influence on development of disorders leading to death

Carlson and Hoelzel also found that fasting rats had retarded development of mammary tumors, both in terms of age of onset and size of tumor, proportional to the amount of fasting. The following table from their paper displays the data.



Mammary tumors occurred in 37% of ad libitum female rats, compared to 29% of females fasted 1 day in 4 , 36% of those fasted 1 day in 3, and only 7% of those fasted 1 day in 2.

Average weight of tumors in ad libitum females equaled 193 g, versus only 67 g in rats fasted 1 day in 4 and 36 g in those fasted 1 day in 3.

Rate of tumor growth was +134 g/100 days in ad libitum rats, +48 g/100 d in rats fasted 1 day in 4, +42 g/100 d in rats fasted 1 day in 3, and +13 g/100 d in rats fasted 1 day in 2.

IF extends healthy lifespan

Carlson and Hoelzel thus showed in 1945 that intermittent fasting 1 in 3 days extends healthy lifespan of rats by 15-20% compared to ad libitum feeding, without daily food restriction (hunger), restriction of protein intake (these rats had 30-35% protein diets), impairing healthy lean tissue growth, or causing extreme loss of body mass.

It looks to me like IF offers a rational alternative to daily caloric restriction.

Top Ten Problems With Applying The Paleolithic Diet Principles: Number 10

When I wrote The Garden of Eating (hereafter GOE), I still had not totally gotten past all the false beliefs I held about dietary fats and the benefits of eating lots of fruits and vegetables. Since publishing The Garden of Eating, I have continued to learn and refine my understanding and practice of Paleolithic diet, and along the way I have discovered a number of ill-founded mistakes I made and that I think others make in applying paleo diet principles to modern life. Rectification of these errors in my own practice have resulted in improvements in my health and body composition. So, in the next 5 to 10 posts I will report and explain the most important errors that create problems for would-be paleodieters, and how to correct them.

10. Eating on an agricultural schedule

In the GOE, we laid out meal plans that suggested three to four meals daily. Like many people, at the time I still believed that research had shown that people need to eat every four to five hours to prevent a decline in metabolism, stabilize blood sugar, and maintain a supply of amino acids to prevent loss of lean mass. Since then, I have learned otherwise. We have no scientific support for frequent eating, especially not in the context of a Paleolithic diet.

When I attempted to eat palediet four meals daily, I frequently found that I simply did not have an appropriate hunger for each meal. Also, I intermittently had bouts with indigestion, abdominal bloating, and constipation triggered by eating foods rich in fat. At times, I literally felt fed up with eating protein and fat, and would gravitate toward eating more tubers and fruits.

So I started questioning. My experience suggested that either people aren’t physiologically adapted to eat a diet high in fat and protein, or that my application of paleodiet principles contained some error. Ethnographic, archaeological, anatomical, and clinical trial evidence all ruled out the former alternative, so I figured the problem lay in my application of the diet.

What did I do wrong? Recent hunter gatherers typically consumed only one or two main meals in a day, often after spending a morning and early afternoon hunting or gathering mostly on an empty stomach. At these meals, H-Gs ate large amounts of animal protein and fat. The human gut has several characteristics indicating adaptation to intermittent feeding on high caloric density foods:

1. A relatively small stomach (only about 20 percent of total gut volume) despite large energy requirements, indicating adaptation to consuming high energy density, i.e., high fat foods.
2. Most (about 65 percent) of gut volume in the small intestine, a characteristic which seems more appropriate for prolonged inter-meal digestion and absorption periods than for frequent feeding.
3. A well-developed gall bladder, which stores bile for intermittent use on demand to emulsify fats for enzymatic digestion, and which only empties efficiently with large doses of dietary fat (See Barry Groves’s good discussion of how low-fat diets cause gallstone formation).

Three meals or more in a day developed only after the rise of agriculture and the adoption of high carbohydrate diets. A constant high meal frequency requires constant presence of stored food, which requires either non-perishable staple foods like grains or a ready refrigerator, neither available to hunter-gatherers.

If you eat a low-fat, high-carbohydrate diet, you will very likely be driven to eat frequently by the insulin response to the high-carbohydrate intake, which locks up your fat stores and drives down your blood sugar, putting you in the constant pincer grip of hunger. Frequent eating and its attendant fluctuations in blood sugar and insulin surges also promote daytime fatigue as energy goes into digestion, activating the parasympathetic—rest and digest—nervous system.

However, if you eat a paleodiet based largely on fat and protein, eating too frequently will not give your liver adequate time to produce sufficient bile for smooth digestion of fats, and you may get the kinds of digestive problems I mentioned above, along with the impression that you don’t or can’t tolerate a high fat diet. It could cause you to question or abandon paleodiet.

Of interest here, eating too frequently could also promote colon cancer by prolonging the colon’s exposure to bile acids. Wei et al did a case-control study (correlation, not causation) found a 50% lower risk of colon cancer among men, but not women, eating fewer than three meals daily. This weakly supports the hypothesis that humans are adapted to eating fewer than 3 meals daily.

Further, if you eat animal protein in Paleolithic quantities, this will by nature reduce your appetite for many hours, which signals that your body is not ready to eat. During this period your liver works intensively converting amino acids to glucose. Naturally, this would tend to reduce your appetite for animal protein.

Finally, a reduced carbohydrate intake reduces your insulin level, and this allows the body to mobilize fat stores so that you can go longer between meals. In other word, if eating paleo, you will have a low normal blood sugar level (due to low carbohydrate intake) and you will run on fat, not sugar, so you won’t have eat to “stabilize your blood sugar.”

We have no evidence that anyone must eat every few hours to avoid a depression of metabolic rate. Studies of fasting have shown that people can go at least 72 hours without food with no decline in metabolic rate, and no loss of lean tissue, and, once the fat starts flowing, no loss of energy. Webber and McDonald even found an increase in metabolic rate after 36 hours of fasting [Br J Nutr. 1994 Mar;71(3):437-47].

We also have no evidence for the claim that you must eat protein several times daily to prevent loss of muscle, or promote gain of muscle. In fact, Stote et al showed that when people ate all their daily caloric requirement in one meal (in a four hour period) daily for eight weeks, they gained muscle and lost fat, whereas when they ate the standard three meals daily they did not experience this body recomposition. The infrequent feeding regimen also reduced cortisol levels, suggesting a reduction in physiological stress.

During a 24 hour fast GH output increases markedly; the frequency of GH pulses increases by 25%, the peak amplitude of GH pulses doubles, and the interpeak serum GH levels quadruple [read this and this]. A study by Norrelund et al indicates that the protein-retaining effects of GH inhibit muscle-protein breakdown during fasting. Fasting-induced increases in GH may therefore account for the increase of lean mass found in the Stote et al study mentioned above.

Since the release of GOE, I have reduced my own meal frequency to not more than thrice daily, most usually eating only twice daily, with both meals consumed in a 6-8 hour window, so that I now fast 16-18 hours daily. This has improved my digestion and elimination, my energy level, my mood, and my body composition (less fat, more muscle). My next book will explain how to adopt this intermittent fasting schedule in a systematic fashion.

Stay tuned for the next installment, we have nine to go.