Are You Eating Too Much Protein? Scientists Finally Weigh In

Ask anyone who lifts regularly how much protein they get each day, and you’ll probably hear anywhere from 1.2 to 2 grams per kilogram of body weight. If you’re 150 pounds, that’s about 136 grams—and plenty of serious lifters go well beyond that. But for years, people have asked: Is that even healthy?

Rumors have circulated for decades, claiming that too much protein could damage your kidneys, stress your liver, or even weaken your bones. But new research shows there’s no solid evidence that high-protein diets are harmful, especially in healthy individuals.

A new study published in The American Journal of Clinical Nutrition found that most of the concerns people have about high-protein diets aren’t backed by solid science. To test this, researchers dug through nearly 60 years of data on claims linking high protein intake to issues like kidney damage, liver strain, bone loss, cancer risk, and more. What they found might surprise you.

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"Results from some observational studies have shown associations of high(er) protein intakes with a variety of negative health outcomes," the study authors said. "However, we know of no compelling evidence that, in otherwise healthy humans, there is an upper level of protein intake where the conjectured harms of HP (high-protein) intake have been demonstrated."

According to the new research, many earlier studies have a major flaw: They were conducted on animals, not humans. Others rely on correlation rather than causation, which can skew the results and lead to misleading conclusions.

On the flip side, plenty of research suggests that more protein is generally better. While there’s clearly a limit to how much you should eat (though it hasn’t been firmly established yet), a study in the Strength and Conditioning Journal found that higher protein intake can support body recomposition, fat loss, and muscle growth. Other research also shows it helps to reduce cravings, lowers blood pressure, and even improves bone density, something especially important as you get older.