Study shows that high protein does not affect kidney function across a wide variety of metrics. Digest
“We’ve got 40 years’ worth of data with people on [protein supplementation] now. And we’re not seeing some sort of rife wave of people who used it getting various forms of cancer, etc., which you would expect. Forty years is enough to see the effect.” - Stuart Phillips, Ph.D. on high protein supplementation
High protein intake is often believed to be harmful to kidney function, but robust evidence indicates that this concern is unfounded. A 2000 study demonstrated that athletes with high protein consumption do not have an increased risk for kidney dysfunction.
Researchers asked bodybuilders and other athletes to keep detailed dietary records for one week after following their normal dietary patterns for one month. Then the researchers assessed the participants' kidney function via blood tests and urinalysis. They also measured their nitrogen balance – an assessment of the net balance of protein metabolism in the body drawn from estimates of nitrogen losses that occur via urine, feces, sweat, and other means.
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They found that, on average, daily protein intake was approximately 1.97 grams per kilogram of body weight among the bodybuilders and 1.35 grams per kilogram of body weight among the other athletes. Despite their high protein intake, the participants' urinary output of creatinine, urea, and albumin was normal, as were other kidney health parameters. Both the bodybuilders and the other athletes achieved nitrogen balance when their daily protein intake exceeded 1.26 grams per kilogram of body weight.
The current recommended dietary allowance for protein intake is 0.8 grams per kilogram of body weight (~0.36 grams per pound) per day – about 68 grams for a 150-pound adult. Nutrition experts established this guideline several decades ago, based on evidence from nitrogen balance studies, which are often inaccurate due to problems with collection and overestimation of losses. Based on findings from more recent stable isotope studies, which more accurately assess muscle protein anabolism and catabolism, evidence suggests that eating 1.2 to 1.6 grams of protein per kilogram of body weight is likely optimal for muscle protein synthesis, especially as one ages. Learn more in this episode featuring Dr. Stuart Phillips.