Do very high protein diets have any potential benefits for health or fitness?
The international Society of Sports Nutrition maintains that sufficient research indicates that individuals engaged in strength training may require 1.6 to 2.0 g protein per kg body mass per day.1 That's twice the requirements of sedentary individuals.
Given this as the established protein need of people engaged in strength training, bodybuilding, and other strength sports, Antonio et al. argued that a diet does not qualify as a high protein diet unless it provides more protein than baseline requirements.2 By this definition, the phrase “high protein diet” would apply only to diets that provide more than 2.0 g/kg/d.
So, what happens to people when they eat a high protein diet?
Antonio et al. set out to find out the effects of consuming a high protein diet on body composition in resistance training individuals.2 The 30 study subjects, all healthy resistance-trained individuals, were randomly assigned to either a control (CON) or high protein (HP) diet.
The CON group was instructed to maintain their habitual diet and training routines for the course of the 8 week study. The HP group was instructed to increase their protein intake to 4.4 g per kg body mass per day (about 2 g per pound of body weight), but to otherwise maintain their training and dietary habits. They could use either whole foods or protein supplements to achieve the increased protein intake.
Over the course of the 8 weeks, the HP group consumed an average of 307 g protein per day, compared to 138 g per day for the CON group. The HP group got 4.4 g/kg/d, while the CON group got 1.8 g/kg/d. This was probably the highest intake of dietary protein ever recorded in the scientific literature.
As a result of their increased protein intake, the subjects in the HP group increased their average total energy intake from 2042 kcal/d before the intervention, to 2835 kcal per day after, averaging 39.9 kcal/kg/d. The control group did not have an increase in energy intake, and averaged 2052 kcal/d (26.2 kcal/kg/d).
Worthy of note, the HP groups also consumed an average of 3.2 g/kg/d carbohydrate, amounting to 226 g per day, not significantly different from the 227 g/d of the CON group. The HP group also consumed slightly more fat per day than the CON group (87 v. 77 g, respectively). These were not low carbohydrate diets.
Despite the increased kcalorie intake for 8 weeks, the HP group did not gain any body fat. This result resonated with the results of an earlier study by Bray et al. which found that excess calories from fat and carbohydrate contributed to fat mass gains, but excess calories from dietary protein (up to 25% of energy) contributed only to lean mass gains.3
It has been shown that overfeeding with equal kcalorie amounts of either fat or carbohydrate results in similar net fat gains; i.e. kcalorie for kcalorie, excess dietary fat and carbohydrate are equally fattening.4
In a follow-up study, Antonio et al. randomly assigned 48 healthy, resistance-trained men and women to two different protocols.5 One consumed their normal protein (NP) diet providing about 2 g/kg/d, while the other consumed a high protein (HP) diet providing more than 3g/kg/d. Both groups participated in a split-routine, periodized heavy resistance training program. They trained 5 days weekly for 8 weeks.
The HP group subjects consumed more total kcalories (2614) and protein (3.4 g/kg/d) compared to the NP group (2119, 2.3 g/kg/d).
As shown in the table below, at the end of 8 weeks, the two groups had gained an equal amount of lean mass (1.5 kg), but the high protein diet group had lost 5 times more fat, and decreased body fat percentage by 1.6 more percentage points.
In this study, the subjects in the HP group had 2.5 more years of training experience than those in the NP group. Since a trainee gets closer to his/her genetic potential the longer he/she trains, and it becomes harder to gain lean mass the more training experience one has, it is expected that trainees with more experience will gain less lean mass than less experienced trainees over any given time period. The fact that the more experienced trainees gained the same amount of lean mass as the less experienced trainees in this study suggests that the high protein diet improved their response to the training.
However, this needs further confirmation, because it is possible some of these more experienced subjects were detrained when starting this program, and simply regaining previously lost lean tissue. In addition, the authors report that the HP group was more compliant with the training program. One might speculate that the higher protein diet also made it possible for the HP subjects to be more compliant with the training. Perhaps the NP group experienced slower recovery from the training sessions, making them more reluctant to complete all sessions, hence less compliant.
This study included performing a basic metabolic panel blood analysis on all subjects. There were no changes in any of the blood variables measured in either group. It appeared that the very high protein diet had no deleterious effects on blood values.
In a follow-up on this last finding, Antonio et al. followed 12 healthy resistance-trained men for 16 weeks (4 months) during which they consumed a habitual protein diet for 8 weeks followed by a high protein diet (more than 3 g/kg/d) for 8 weeks, or vice versa, in a randomized crossover design.6
Once again, the subjects consuming the high protein diet consumed an approximate 400 additional calories daily for 8 weeks, yet on average had no increase in fat mass. In fact, 9 of the 11 subjects demonstrated a decrease in fat mass during the high protein diet phase. However, the other 2 subjects had an increase in fat mass, suggesting that most (~70%) people will not experience fat mass gain from eating additional protein above energy requirements, but some (perhaps 30%) might have a different response.
It is unclear why these two individuals differed from the others. It is possible that they gained fat due to some dietary change/factor other than the increased protein. However, it also may be that some people respond differently to increased dietary protein. Individuals vary and this is why only you can determine what works best for you.
In addition, the study found that eating a high protein diet had no deleterious side effects on blood lipids, glucose, kidney or liver function, etc.
Of interest, the average cholesterol intake of subjects in this study was as much as 160% greater than the typical recommendation of only 300 mg per day, but the HP and NP groups had low total cholesterol levels of 152 and 143 respectively, and LDL of 91 and 86 respectively. Thus a very high protein diet along with high cholesterol diet had no adverse effect on conventionally accepted (but questionable) blood lipid risk factors for cardiovascular disease.
I was also interested to see that these subjects also had triglyceride levels higher than HDL levels. This may have been due to their consuming a relatively high carbohydrate, low fat diet.
In any case, these studies suggest that overeating protein may not contribute to body fat stores in a majority (perhaps 70% or more) of individuals, and it might improve lean mass gains in combination with a progressive resistance training program.
T. Colin Campbell, Ph.D. and his team have published research findings from rat studies suggesting that high protein diets promote cancer. According to Campbell, consumption of any diet containing more than 10% animal protein in the form of casein promotes cancer, while diets rich in plant protein – up to 20% of energy as soy or gluten protein – do not.7,8
The problem with Campbell's research is that both wheat protein (gluten) and soy protein are incomplete proteins for rats (and humans). When used as sole protein sources, wheat is deficient in lysine, and soy, methionine. This is especially true for rats which have higher protein requirements than humans. (A 1979 study showed that human infants fed soy protein-based formula without methionine added were undernourished.9)
In fact, Campbell’s team showed that if rats were given wheat protein with additional lysine to raise the total diet protein quality to equal that of casein, the wheat protein diet did not differ from the casein diet in cancer promotion.10
Another problem is that all of Campbell’s research focussed on cancers induced by exposure to enormous levels of aflatoxin, equivalent to humans eating 270,000 100-gram servings of peanut butter daily. Even if a protein-deficient diet did help prevent growth of aflatoxin-induced liver cancer, this would not necessarily indicate that such a diet would help prevent cancers due to other causes.
In other words, at best, Campbell’s research shows that diets based on plant proteins will only block or retard aflatoxin-induced cancer growth if the diet is deficient in some amino acids.
Since to maintain health any person eating a plant-based diet needs to consume a variety of proteins and achieve a complete amino acid intake, Campbell’s research10 also shows there will most likely be no difference in cancer promotion between a properly balanced plant-based diet providing all essential amino acids, and a diet in which animal protein is consumed.
Since both normal and cancer cells require complete proteins for maintenance and growth, it seems unlikely that manipulation of protein intake can strongly favor healthy cells over malignant cells. Restricting protein quantity or quality will likely harm healthy cells – including the immune cells that fight cancer cells – as much as it would harm cancer cells.
In contrast, it is well established that cancer cells differ from healthy cells in mitochondrial function and energy metabolism. Specifically, cancer cells are more dependent on metabolism of glucose meet their energy and substrate needs.11 This suggests that cancer could be controlled by limiting its supply of glucose. Restricting glucose availability will not negatively affect healthy cells which can burn fat (and obtain glucose from metabolism of the glycerol backbone of triglycerides).
In view of this, Ho et al. performed a study with mice to find out whether low-carbohydrate (CHO), high protein diets could decrease blood glucose levels enough to slow tumor growth or reduce tumor incidence.11 They chose to test a high protein diet rather than a high fat diet because some studies report high fat diets promote tumor growth while others suggest amino acid supplementation has anti-tumor benefits.
They fed mice different levels of CHO and protein and found different effects:
All low CHO diets reduced insulin and lactate levels, with the 8% and 10% diets producing the lowest levels. They found that there was a positive correlation between plasma insulin levels and tumor size (i.e. higher insulin –> bigger tumors).
Further, they found that a 15% CHO diet dramatically reduced tumor incidence in spontaneous tumor-prone rats. At 1 year of age, almost half of mice on a conventional diet had developed spontaneous tumors, compared with none on the 15% CHO diet.
Ho et al. reported: “Furthermore, 70% of mice on the 5058 [conventional] diet developed tumors during their lifespan, with only 1 reaching normal life expectancy, whereas less than 30% of the mice on the 15% CHO diet developed tumors, with more than half reaching or exceeding normal life expectancy.”
Ho et al. found no evidence of kidney damage or other adverse effects among these animals consuming very high protein diets. In fact, the mice eating the high protein diets lived beyond the normal life span of mice given a conventional “Western” diet.
The authors reported no financial conflicts of interest and the study was supported by non-profit agencies.
These data suggest that a very low carbohydrate, very high protein diet can reduce the incidence and growth of spontaneous breast tumors in mammals, possibly by reducing insulin levels and blood glucose supplies to tumors.
Studies of the fat yield from fully dressed wild ungulates eaten by hunter-gatherers indicate that they would have provided a moderately high fat, high protein diet. Game animals are too lean to support a very high fat, low protein diet without wasting very large amounts of edible meat.
Inuit have subsisted for hundreds or thousands of years on a carnivorous, very low-carbohydrate diet living in conditions perhaps similar to those of the Ice Ages in Europe. They consume some of the fattest land and sea mammals in the world: musk ox, polar bear, whales, seals, walrus.
Heinbecker reported that an average adult Eskimo would consume 4 to 8 pounds of meat in a day, and the estimated average daily macronutrient intake was 280 g protein, 135 g fat, and 54 g carbohydrate (mostly from glycogen in the meat eaten).12 This amounts to 2551 kcal, 43% protein, 48% fat, and 8% protein. Other investigators have reported protein intakes among Inuit ranging from 43% energy to 56% energy (see table below).13
Thus the Eskimos/Inuit had protein intakes similar to the levels investigated by Antonio et al.2,5, 6 and reaching close to the levels investigated by Ho et al.11
Medical investigators found no evidence of atherosclerosis, diabetes mellitus, appendicitis, cancer, dental caries or tuberculosis in Eskimos living on a traditional carnivorous diet. One medical professional who directly studied the Eskimos on their native very high protein diet described them as “peaceful, extremely happy and healthy.”14
The diet of preagricultural Europeans – Neanderthal and H. sapiens sapiens – appears to have been similarly highly carnivorous, similar to that of the arctic fox.15,16 Under those conditions, natural selection would have favored the survival of individuals who obtained health and fitness benefits from high intakes of animal protein.
Bear in mind that most published research findings are false17 often due to small study size, financial interests involved, or prevailing biases in the fields of study. The findings discussed above involved relatively small study populations, reducing their reliability. However, the investigators did not report any financial stake in the outcomes of their research. Further, these findings contradict common biases in the nutrition field, since it is commonly believed that a calorie from protein is just as fattening as a calorie from fat or carbohydrate, that high protein diets are harmful to the liver and kidneys, and that high protein diets promote cancer.
Furthermore, these research findings resonate with what is known about preagricultural diets of humanity and health of hunter-gatherer populations. Since during the Ice Ages humans – especially Europeans – subsisted on high animal protein diets, it is expected that we would be adapted to and benefit from high animal protein diets.
As well, it is fairly well-documented and widely accepted that hunter-gatherers living on high animal protein diets (19-35% of energy) displayed a very high immunity to diseases of civilization, including those commonly believed to be caused by high animal protein diets, such as heart disease and cancer.18, 19
Nevertheless, because individuals vary, one should only take them as indicating possibilities for personal experimentation and confirmation, namely:
High protein diets might help you reduce your body fat, increase your lean mass, and, if also very low in carbohydrate, reduce your cancer risk.
Your results might vary from the findings reported above, but you will never know unless you experiment. The indoctrinated analytical mind is not likely the best guide to what to eat. The history of science has proven that scientific consensus is no guarantee that scientists' beliefs accurately represent reality. Scientists also fabricate and falsify research findings, especially in medical/pharmaceutical research.20
No other species relies on an educated analytical mind or "science" to determine what to eat. Nor did our uncivilized ancestors rely on authorities to tell them what to eat. Instead, they trusted their traditions and common senses of appetite, hunger, taste, and satisfaction to guide them, choosing natural foods that tasted good and satisfied both appetite and hunger.
If you have an appetite for, greatly enjoy, and feel greatly satisfied by eating high protein animal foods, this may indicate that your body is naturally adapted to a high protein diet. We recommend that you learn to trust your true nature and senses of appetite, hunger, taste and satisfaction to guide you to optimum natural food selection to best fit your unique, individual constitution and needs.