April 25, 2000 -- If you eat a standard American diet, there's a good chance that you are ingesting a lot more protein than your body actually needs. On average, Americans and Western Europeans consume between one-and-a-half and two times the daily recommended intake established by the World Health Organization, according to a study in the April issue of the Journal of Nutrition. And despite the popularity of protein diets these days, excess protein does not help -- and may hurt -- the body, report Cornelia Metges and colleague Christian Barth of the German Institute of Human Nutrition in Germany in an analysis of existing research on the subject.
Also, while a number of athletes and body builders believe that a high-protein diet is crucial to their physical performance and training, Metges and Barth found no evidence in the scientific literature to support this assumption.
"I don't think there's any evidence to support [the notion] that adding high amounts of protein plays an important role for athletic training," Steven Heymsfield, MD, tells WebMD, "although they buy [protein supplements] like crazy and waste their money. If you take in too little protein, you lose body protein. If you take in too much, you just burn it as calories." Heymsfield is a professor of medicine at Columbia University in New York City and at the Obesity Research Center at St. Luke's-Roosevelt Hospital. He was not involved in the study.
In addition to not providing any benefit to general health, eating a high protein diet may have adverse effects, some research has suggested. The authors cite several studies that have found associations between excess protein in the diet and kidney disease. Another study suggests a relationship between high protein intake and prostate cancer, and a Japanese study explored the association between diabetes and protein.
Despite the number of studies associating high protein intake with certain illnesses and conditions, the subject is still open to controversy. "There's no reason for healthy individuals to consume protein in amounts above the recommended levels," says Heymsfield, but he is not certain that it will actually lead to health problems. "The effects of protein are very subtle. It's hard to answer if high protein diets are unsafe."
High protein weight loss programs have seen a recent resurgence in popularity. Joni Pagenkemper, MS, MA, RD, an assistant professor of nutrition and dietetics at Loma Linda University in California, believes they are popular because people initially see quick results. "But for long-term, we don't know if they are safe," Pagenkemper tells WebMD. She points out that protein in this type of diet tends to come from animal sources, which are also high in saturated fats and bring with them other problems such as a risk for heart disease.
Due to the lack of data, conclude the researchers, a maximum intake level for protein cannot be determined for a healthy adult population. But because of the possible adverse effects, they believe that it is prudent for healthy adults not to eat amounts of protein far above the recommended levels.
"Taking in excess protein means you'll just be excreting it," Pagenkemper says. "Basically, high protein is just an expensive way to feed yourself."
- Americans and Western Europeans typically consume up to twice the amount of protein recommended by the World Health Organization.
- Scientific studies show that consuming large amounts of protein offers no benefit, even for athletes, and it could be harmful instead.
- Weight loss programs that include a high-protein diet are controversial, because they offer results quickly, but experts question their long-term safety.