High-protein diets are popular in weight training and bodybuilding circles. Some of these diets are in the range 30% protein, and some even higher than that. This is beyond the usual dietary requirements, even for athletes, and we should question if this is a safe level of dietary protein over the long term.
The consensus among professional sports nutritionists is that protein requirements for athletes -- even strength athletes -- will not exceed 0.9 grams/pound (2 grams/kilogram) of body weight -- and mostly less is required. The recommended daily intake in dietary reference values is 0.37 grams/pound per day (0.8 grams/kilogram/pound).
If we consider a 176 pound (80 kilo) strength athlete, 30% by energy of protein on an average 3,500 calorie/day diet is 1,050 calories and 262 grams of protein. That's well over the estimated maximum requirement of around 160 grams for that body weight at 0.9 grams/pound/day. A 30% protein diet is excessive and there is little justification for this quantity of protein in this context.
What's Wrong With High-Protein Diets?
While various interest groups will point to hunter-gatherers who ate high-protein diets -- the Inuit and Masai for example -- and high-meat diets in Paleolithic populations, this does not necessarily show that excessive protein consumption is healthy for modern communities, taking into account genetics and even the shortened longevity of these high-protein populations.
The following points of potential adverse effect of too much protein are not new, but they are worth ongoing evaluation.
Kidney Disease and High-Protein Diets
The long-term effects of high-protein diets on kidney disease are still poorly understood. People with chronic kidney disease are often told to go on a low-protein diet because this has some protective effect on worsening kidney function. However, the question as to whether high-protein diets cause kidney disease is not established.
Even though most studies of healthy, athletic people have not shown any permanent adverse effects of high-protein diets on the kidneys, long-term studies of sufficient quality have not been done. It's possible that obese people entering exercise and weight training programs might have undiagnosed chronic kidney disease for which such diets would not be appropriate.
Bone Health and High-Protein Diets
It's likely that diets high in protein, especially animal protein, cause acid conditions in which calcium is released from bone in order to reduce that acidity. This could cause a net loss in bone leading to osteoporosis. Some studies show that this is possible and others show that too little protein is not good for bone health either.
An optimum quantity and quality of protein for bone health seems likely and that too much or too little might cause adverse effects.
Nutritional Adequacy of High-Protein Diets
Most of our vitamins and minerals come from plant foods like fruit, vegetables, nuts, beans, seeds and whole grains -- much of which is delivered with carbohydrate. Increasing protein in the diet means either fat or carbohydrate must be reduced. If carbohydrate sources are reduced, the overall nutritional adequacy of the diet could suffer unless careful consideration is given to food selection.
For example, a study in the Journal of the American Dietetics Association in 2007 looked at the following diets and eating plans for compliance with the Harvard School of Public Health's Alternate Healthy Eating Index:
New Glucose Revolution, Weight Watchers, Atkins, South Beach, Zone, Ornish, 2005 US Department of Agriculture Food Guide Pyramid
Here is the order in which the diets complied best with the healthy eating index, and the scores out of 70 (the higher the score, the healthier the diet):- Ornish very low fat (score 64.6)
- Weight Watchers high-carbohydrate (score 57.4)
- New Glucose Revolution (score 57.2)
- South Beach/Phase 2 (score 50.7)
- Zone (score 49.8)
- 2005 Food Guide Pyramid USDA (score 48.7)
- Weight Watchers high-protein (score 47.3)
- Atkins/100-g carbohydrate (score 46)
- South Beach/Phase 3 (score 45.6)
- Atkins/45-g carbohydrate (score 42.3)
You can see from this analysis that high-protein diets -- Atkins, South Beach and others -- fared worse than their high-carbohydrate (and plant) diets. The higher your protein intake, the less likely you are to meet recommended daily intakes of all essential nutrients over time.
Longevity and High-Protein Diets
Two studies have looked at how people fare on high-protein diets over time. In Swedish and Greek studies, adults were followed for 10 years and deaths analyzed in relation to diets higher in protein and lower in carbohydrate. Both studies found that prolonged consumption of diets low in carbohydrates and high in protein were associated with a significant increase in total mortality (death).
Summary of High-Protein Diet Safety
What this boils down to is that very high-protein diets in the modern context have not been studied adequately for safety. We know that hard-training athletes need some extra protein in the diet. An upper limit of 0.9 grams per pound of body weight is over twice the recommended adequate intake, so it's still a high-protein diet, yet one that may be justified for training. Bodybuilding diets well in excess of this cannot be justified on performance or safety grounds.
Sources
Friedman AN. High-protein diets: potential effects on the kidney in renal health and disease. Am J Kidney Dis. 2004 Dec;44(6):950-62. Review.
Tipton KD, Wolfe RR. Protein and amino acids for athletes. J Sports Sci. 2004 Jan;22(1):65-79. Review.
Ma Y, Pagoto SL, Griffith JA, et al. A dietary quality comparison of popular weight-loss plans. J Am Diet Assoc. 2007 Oct;107(10):1786-91.
McCullough ML, Willett WC. Evaluating adherence to recommended diets in adults: the Alternate Healthy Eating Index. Public Health Nutr. 2006 Feb;9(1A):152-7.
Lagiou P, Sandin S, Weiderpass E, et al. Low carbohydrate-high protein diet and mortality in a cohort of Swedish women. J Intern Med. 2007 Apr;261(4):366-74.
Trichopoulou A, Psaltopoulou T, Orfanos P, et al. Low-carbohydrate-high-protein diet and long-term survival in a general population cohort. Eur J Clin Nutr. 2007 May;61(5):575-81
