Your high-protein diet is likely much safer than many mainstream nutritionists like to believe

By Jordana Brown


Didn’t I hear something about kidney damage occurring from too much protein?



“The break down of amino acids results in the formation of ammonia,” says Tabatha Elliott, PhD, who has extensively studied protein at the University of Texas Medical Branch (Galveston). “The ammonia is then converted to less harmful urea in the liver and is then passed through the kidneys and excreted in urine.” Because it’s the job of the kidneys to take away any excess protein that your body’s not using, mainstream nutritionists worry that eating excess protein could tax your kidneys.

However, several studies have shown that this just isn’t the case. One study, presented at the International Society of Sports Nutrition’s annual conference in 2005, examined the diets of 77 resistance-trained males and then tested their blood for various markers of kidney health. The subjects were eating about 0.8 grams of protein per pound of bodyweight per day, and their kidneys were in perfect health. Another study, conducted at the Free University of Brussels (Belgium), found similar results for people consuming roughly 1.3 grams of protein per pound.

There is very strong evidence that athletes who are taking in more protein are actually using that protein, either to build muscle or to burn as fuel, and therefore, because their bodies don’t have a glut of protein to excrete, there’s little reason to be worried about kidney health.

What about my bones? Can’t high protein intake make them brittle?

There have been some studies that have shown that high amounts of protein in the diet can increase the amount of calcium the body excretes, which could potentially lead to fractures and osteoporosis, but those studies mostly involved purified protein, and not whole-food protein sources like meat. “But I drink three protein shakes a day,” you say, panicking. “Isn’t that purified protein?” We hear you. But the fact that you also eat whole food protein sources like chicken and steak should provide you with enough calcium-protecting phosophorous and other nutrients. That, at least, was the finding of one study published in the Journal of Nutrition in 2003. Subjects were fed either a high-meat or low-meat diet for eight weeks, and researchers found that there was no difference in calcium excretion between the groups.

Still worried? A study at Warsawa Agricultural University (Poland) showed that, in rats at least, a high-protein diet actually increased bone mineralization, meaning the rats that ate more protein had stronger bones. And also, keep in mind that resistance exercise (aka lifting weights) is one of the best things you can do to keep your bones strong.

Flex recommends you get at least one gram per pound of bodyweight per day of quality lean protein and drink protein shakes around workout time to make your muscles — and the rest of you — happy.