Does Eating a High-Protein Diet Harm You?

People frequently ask whether the high-protein intake of adults in North America is harmful. The extra vitamin B-6, iron, and zinc that accompany protein foods are often beneficial. However, high-protein diets typically may be low in plant foods and, so, low in fiber, some vitamins (e.g., folate), some minerals (e.g., magnesium), and phytochemicals. As well these diets are typically rich in saturated fat and cholesterol, and thus do not follow the recommendations of the Dietary Guidelines for Americans or the Food and Nutrition Board.

Some studies show that high-protein diets can increase calcium loss in urine. Certain types of amino acids-especially some of those rich in animal proteins-cause this effect. Based on the research to date, it is reasonable to assume that individuals who have inadequate calcium intakes are further compromising bon health by consuming excessive amounts of protein. (However, many people have calcium-deficient diets.) The increased calcium loss may also contribute to kidney stone formation in people who have a history of forming such stones. Thus such persons should not consume a high-protein diet.

Excessive intake of red meat, especially processed meats such as ham and salami, is linked to colon cancer in population studies. This link could be attributable to the protein or fat in the food products or to substances that are used during processing (e.g. nitrates/nitrites) or those that form during cooking of red meat at high temperatures (e.g. heterocyclic amines). Excessive fat intake associated with diets rich in red meat, or low-fiber intake, may also be a contributing factor. Because of this concern with red meat, some nutrition experts suggest we focus more on poultry, fish, nuts, legumes (beans), and seeds to meet protein needs. In addition, any meat should be trimmed of all visible fat before grilling.

Some researchers have also expressed the concern that a high-protein intake may unduly burden the kidneys by forcing them to excrete the resulting excess nitrogen as urea. Low-protein diets marginally slow the decline in kidney function in humans if begun early in the course of developing kidney disease, and laboratory animal studies show that protein intakes that just meet nutritional needs preserve kidney function over time better than high-protein diets. Preserving kidney function is especially important for people with diabetes, for people without diabetes or kidney disease, the risk of suffering kidney failure is very low; thus, the risk of a high-protein diet’s contributing t kidney disease (aside from kidney stones) in later life is also low.

The amino acids most likely to cause toxicity when consumed in large amounts are methionine and tyrosine. The potential for amino acid imbalances and toxicities is too great to recommend that any be taken individually as supplements. As emphasized earlier, the body is designed t handle whole proteins as a dietary source of amino acids. When individual amino acid supplements are taken, they can overwhelm the absorptive mechanism in the small intestine, triggering amino acid imbalances in the body. These imbalances occur because groups of chemically similar amino acids compete for absorption sites in the absorptive cells. An excess of one can hamper other amino acids form being absorbed. Overall, every amino acid taken in excess can be harmful. We should stick to whole foods as sources for amino acids.

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