LETTER TO THE EDITOR
High-protein diets: Putting rumors to rest
Anssi Manninen, MHS
Department of Physiology, Faculty of Medicine, University of Oulu, PL 5000, 90014 Oulun Yliopisto, Finland
(Email: anssi.manninen{at}oulu.fi).
"One could not be a successful scientist without realizing that, in contrast to the popular conception supported by newspapers and mothers of scientists, a goodly number of scientists are not only narrow-minded and dull, but also just stupid."
J. D. Watson, The Double Helix
I read with great interest the study by Kappagoda et al. (1) on high-protein diets. Unfortunately, they quoted uncritically the American Heart Association (AHA) Nutrition Committee's statement on dietary protein and weight reduction, which states, "Individuals who follow these [high-protein] diets are at risk for...potential cardiac, renal, bone, and liver abnormalities overall."
Liver abnormalities? That is physiological nonsense. Protein is needed not only to promote liver tissue repair, but also to provide lipotropic agents such as methionine and choline for the conversion of fats to lipoprotein for removal from the liver, thus preventing fatty infiltration (2). And when it comes to kidney function, there are no data in the scientific literature demonstrating that healthy kidneys will be damaged by the increased demands of protein consumed in quantities above the recommended dietary allowance (RDA) (2). Furthermore, real-world examples support this contention because kidney problems are nonexistent in the bodybuilding community in which high-protein intake has been the norm for over half a century. The AHA Nutrition Committee also suggests that high-protein intake may increase blood pressure. However, there is no scientific evidence whatsoever supporting this contention. In fact, a negative correlation has been shown between protein intake and systolic and diastolic blood pressures in several epidemiological surveys (2).
Further, the AHA Nutrition Committee claims that high-protein intake has detrimental effects on bone health. In reality, dietary protein increases circulating insulin-like growth factor (IGF)-1, a growth factor believed to play an important role in bone formation. Indeed, several studies have examined the impact of protein supplementation in patients with recent hip fractures. For example, Schurch et al. (3) reported that supplementation with 20 g protein/day for six months increased blood IGF levels and reduced the rate of bone loss in the contralateral hip during the year after the fracture. Finally, the AHA Nutrition Committee ignores the fact that energy restriction increases protein requirements. It has been known for about a half century that inadequate energy intake leads to increased protein needs (2). Thus, when trying to lose weight, it is important to keep protein levels high. The reduction in calories needed to lose weight should be at the expense of the fats and carbohydrates, not protein.
In summary, the AHA Nutrition Committee's statement on dietary protein contains misleading and incorrect information. Certainly, such public warnings should be based on a thorough analysis of the scientific literature, not unsubstantiated fears and misrepresentations. For a more detailed review, see my recent paper in the Sports Nutrition Review Journal (2).
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- Kappagoda CT, Hyson DA, Amsterdam EA. Low-carbohydrate–high-protein diets: is there a place for them in clinical cardiology? J Am Coll Cardiol 2004;43:725-730.[Abstract/Free Full Text]
- Manninen AH. High-protein weight loss diets and purported adverse effects: where is the evidence? Sports Nutr Rev J 2004;1:45–51..
- Schurch MA, Rizzoli R, Slosman D, et al. Protein supplements increase serum insulin-like growth factor-I levels and attenuate proximal femur bone loss in patients with recent hip fracture: a randomized, double-blind, placebo-controlled trial Ann Intern Med 1998;128:801-809.[Abstract/Free Full Text]
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