Are High-Protein Diets Healthier?

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Last month we looked at the questionable claim that the RDA for protein is inadequate. This claim was largely based on dubious assertions that growing research data is showing that a protein intake significantly greater than the longstanding RDA would be beneficial for treating and preventing sarcopenia. However, an objective review of the best quality data does not support claims that higher-than-RDA protein intake is needed to help prevent sarcopenia. This month, we will examine the scientific evidence linking high-protein diets (especially from animal sources) with a wide variety of known and suspected adverse metabolic effects that almost certainly contribute to adverse effects on health and longevity. 

People Eat Foods — Not Isolated Nutrients

More SAAs and BCAAs lead to increased Hcy and 3-HIB and both tend to increase IGF-1, mTOR, and insulin resistance. This is not compatible with maximizing health and longevity, from my perspective. Higher cooked animal protein intake leads to far more AGEs, HAAs, PAHs, and sialic acid, which likely promote more cancer and perhaps faster aging too. And more than PEP guidelines now allow for animal protein foods would likely lead to increased IGF-1 and mTOR that almost certainly speed up the aging process and promote cancer growth. So there can be little doubt that more than PEP guidelines on even the "cleanest" animal protein foods would elevate a number of proven and suspected disease/aging risk factors. There is no credible evidence that more protein reduces the loss of LBM and strength seen in old age and because it likely speeds up the aging and disease risk factors that promote sarcopenia (which has long been one of two rationales for recommending higher protein intake than PEP currently allows). The second rationale is that higher protein foods confer more satiety/kcal, which is very dubious. The research on the satiety index of foods showed that the highest satiety/kcal food was the potato. There really is no credible evidence that a higher % protein diet than now allowed under PEP guidelines would aid long-term weight loss or improve health or longevity.

Insulin resistance and type 2 diabetes are largely promoted by excessive calorie intake and weight gain. However, there is data showing that saturated fatty acids not only raise LDL-cholesterol levels but also increase inflammation and promote some insulin resistance that is independent of change in body fat stores. Of course, the higher LDL-cholesterol levels seen with higher saturated fat and/or cholesterol intake are also a problem for those with type 2 diabetes, since these patients have at least a two- to three-fold increased risk of atherosclerotic events such as heart attacks or strokes. Another reason to be concerned about diets with more animal protein foods and even those very low in saturated fat and cholesterol is that those diets tend to be higher in branch chained amino acids and specifically valine. Valine is catabolized to 3-hydroxy isobutyrate (3-HIB) in muscle cells and this increased HIB has also been shown to increase insulin resistance in muscle cells that is independent of change in calorie intake or body fat stores. (You can learn more about this at

Another serious health problem that is increasingly being linked to a diet higher in fatty animal products and lower in minimally-processed fiber-rich plant foods is colon cancer. In a study that compared the gut microbes in age-matched men 50-65y living either in rural Africa or in the United States, Dr. Ou and colleagues found much higher levels of Bacteroides and much lower levels of Prevoltella in the African Americans and the reverse in the native rural African men. Prevoltella bacteria thrive on dietary fiber and undigested carbohydrates found in plants, which they ferment into short-chain fatty acids like acetate and butyrate. These short-chain fatty acids are used by colon epithelial cells as a major source of energy and tend to improve their health. Whereas the bactericides thrive in the guts of those consuming more animal products like eggs and meats. Bacteroides produce secondary bile acids and other substances that have long been associated with the development of colon cancer. Colon cancer is at least 10 to 50 times more common in African American men than it is in native African men consuming a largely plant-based diet high in fiber with only small amounts of animal foods.

By James J. Kenney, PhD, FACN


Ou J, Carbonero F, Zoetendal EG, DeLany JP, Wang M, Newton K, Gaskins HR, O'Keefe SJ. Diet, microbiota, and microbial metabolites in colon cancer risk in rural Africans and African Americans. Am J Clin Nutr. 2013 Jul;98(1):111-20. doi: 10.3945/ajcn.112.056689. Epub 2013 May 29

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