You might be eating too much protein

Growing up, many of us remember dutifully taking a few more bites of protein (and, of course, vegetables) to appease our moms before we were allowed to progress to the sweet, carb-heavy goodness of dessert. Lately, it seems hard to say whether our moms would be delighted or horrified to see what has happened to protein since.

Just walk into any grocery store right now, and protein is everywhere. Protein water. Protein chips. You can even request protein foam on your favorite fancy latte. Somewhere, a bodybuilder is chugging a protein shake the size of a fire extinguisher as you read this. It’s safe to say this is not your mother’s protein.

To be fair, protein deserves at least some of its mom-and-jock-endorsed reputation. It helps build muscles, keeps you feeling full, and is an essential nutrient we truly can’t live without. Older adults, especially, have been told to eat more of it as they age. 

So, is more protein always better? According to a large review of several recent studies, the answer may be no.

“We think of protein as beneficial,” Dr. Dudley Lamming, a professor at the University of Wisconsin-Madison and lead researcher of the review, told Popular Science, “but a number of studies have started to come out showing that when you look at large populations over the course of decades, people who were eating more protein over the course of these decades were having higher rates of age-related diseases.”

A pattern in the data sparked new questions 

Lamming didn’t set out looking for a problem with protein. If anything, he was surprised by a contradiction he was noticing between population data and the conventional wisdom about protein—people who ate more protein over time were showing higher rates of cancer, diabetes, and cardiovascular disease. 

“The question is, how can this be?” he remembers wondering.

Lamming’s review looked at more than 350 studies in total, most of which were conducted in mice and other lab models, examining things like lifespan, metabolic health, and cellular aging. 

But a smaller slice, about five or six randomized trials, tested protein restriction directly in people. Those human trials showed consistent short-term benefits: People lost weight, their fat mass declined, and in one study of people with type 2 diabetes, insulin sensitivity improved.

Lamming adds that these results do not appear to be associated with mere calorie reduction.

“In fact, because dietary protein is satiating, people in our studies and others actually ate more calories when they were on a protein-restricted diet,” he says. “But they lost weight, and that’s because energy expenditure increases.”

One hormone may explain what’s happening

To understand the potential connection between protein restriction and increased energy expenditure, Lamming’s review explored existing mouse studies on the topic. Findings from these studies indicate that when protein intake drops, the liver releases a hormone called FGF21. That hormone signals the brain, which in turn triggers what researchers call “beiging.”

“This is a process that essentially tells your fat tissue to stop simply storing fat, but actually to start metabolizing it and burning it for energy,” says Lamming. 

In practice, protein restriction doesn’t mean cutting protein out altogether. Most people get about 16 to 17 percent of their calories from protein; in the studies Lamming and his team reviewed, that’s typically cut by around half, down to roughly seven to nine percent.

“We’re not talking about restricting to an unhealthy level where you’re protein insufficient,” he says. “What we’re really talking about, in most cases, is restricting down to the recommended daily allowance as reported by the World Health Organization, which is about 0.8 grams per kilogram [of body weight].” 

So the average man (weighing an average of about 200 pounds) would need about 73 grams of protein a day. The average woman, on the other hand, (weighing about 170 pounds) would need 62 grams of protein a day. For reference, a small three ounce filet of salmon contains about 24 grams of protein.

You don’t necessarily have to restrict protein as a whole to achieve these benefits, either; mouse studies found that cutting back on specific amino acids, including methionine, isoleucine, and valine, may provide some of the same benefits in terms of fat mass, blood sugar control, and longevity. 

Exercise may change the equation

This doesn’t necessarily mean everyone should be in a hurry to throw away their protein waffles. Lamming is careful to note that people who exercise routinely may be an exception.

“We actually think that dietary protein has negative metabolic health outcomes for sedentary people, like the general population, since most of the population is fairly sedentary,” he says. “But maybe people who are exercising need more protein to help build muscle, and maybe it wouldn’t have these negative metabolic outcomes.”

Although these findings are based only on mouse studies so far, they may suggest that working out might protect against the downsides of higher protein intake, Lamming says. 

“Fortunately,” he says, “a lot of the people who are very pro-protein are also people who are exercising.”

Lamming says his team plans to test these ideas—specifically, whether protein supplementation genuinely benefits those who exercise, and whether restriction benefits those who don’t—more directly in both mice and people over the next few years.

“For your typical person who’s not engaged in exercise, we would suspect, based on our research, that eating more calories in the form of protein would be detrimental,” he says. 

Lamming’s own suggestion for sedentary people: Consider skipping the protein-added version of a product when a regular option is available.

He was quick to add, however, that those who can safely exercise certainly should.

“No one’s going to argue that more exercise would be bad,” he says.

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