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.