Nutrition

June 19, 2011

High Protein Diets and Kidney Function

A recent New York Times article took to task the all-too-often-expressed claim that high protein diets are bad for the kidneys. After citing some of the relevant research on the topic, the article goes on to conclude: “…studies show that in healthy adults, increased protein intake does not put excess strain on the kidneys.” Hooray for the New York Times for finally acknowledging what those of us who keep abreast of research have known for years! The real question is, What took so long?

The myth that protein is detrimental to the kidneys dates back to the early 1980’s when Dr. Barry Brenner, a nephrologist at Brigham and Women’s Hospital, published several research papers linking high protein diets to the progression of renal disease (1). In short, Brenner claimed that a high protein intake increased glomerular filtration rate (i.e. the volume of fluid filtered in the kidneys), ultimately leading to renal dysfunction. This came to be known as the “Brenner Hypothesis” and was adopted as gospel by a large segment of the nutritional community. To this day, most college nutritional texts continue to espouse the dangers of a high protein consumption on the kidneys.

The problem with the Brenner Hypothesis is that it was based almost entirely on data from animal subjects and those with existing kidney disease. Extrapolating results from such populations to healthy humans is a classic case of improperly generalizing findings. Research 101 dictates that external validity (i.e. generalizability) is limited to the population studied. That’s certainly the case here.

As noted in the New York Times article, research on healthy individuals has continually failed to find any negative correlation between protein intake and kidney problems. While a higher protein consumption does lead to changes in renal size and GFR, these have proven to be normal adaptations with no adverse effects on kidney health (2). And this is not a case of cherry picking studies; results have held true in multiple research trials across a wide variety of demographic groups including athletes, the elderly, and the obese.

In fairness, it should be noted that studies on the topic have been limited to examining an intake of under 3 grams/kg of protein a day. Thus, it is not known if intakes above this amount might cause detrimental effects. However, 3 grams/kg/day is a substantial amount of protein, equating to a daily intake of about 250 grams of protein for a 180 pound guy. What’s more, there’s a large body of anecdotal evidence from athletes who consume extremely high protein diets (sometimes in excess of two times body weight) without displaying associated kidney issues. This would seem to indicate that higher intakes are not an issue but further research is needed for confirmation.

In sum, it’s about time to put to rest the myth that a high protein intake will harm your kidneys. Given that higher protein diets have been shown to be metabolically advantageous for those who are trying to lose weight and/or maintain a healthy body weight, we should be encouraging people to adopt such nutritional practices, not scaring them off with baseless claims.

Stay Fit!

Brad

1) Brenner BM, Meyer TW, Hostetter TH. Dietary protein intake and the progressive nature of kidney disease: the role of hemodynamically mediated glomerular injury in the pathogenesis of progressive glomerular sclerosis in aging, renal ablation, and intrinsic renal disease. N Engl J Med. 1982 Sep 9;307(11):652-9

2) Skov AR, Toubro S, Bülow J, Krabbe K, Parving HH, Astrup A. Changes in renal function during weight loss induced by high vs low-protein low-fat diets in overweight subjects. Int J Obes Relat Metab Disord. 1999 Nov;23(11):1170-7