Protein is the gatekeeper to maximizing muscle and minimizing diet-damaging cravings. But too much of the stuff has been linked with harming your organs, crippling your fat loss, and even causing cancer. Can you really have too much of a good thing?
Let’s start with the numbers: The Institute of Medicine recommends that adults get a minimum of .4g of protein for every pound of bodyweight per day (that’s about 65g for a 175-lb guy). But a study in Applied Physiology, Nutrition, and Metabolism found that that number should be more like .6g to build lean muscle mass. A high-protein diet takes it a notch further and loads you with 1-1.5g per pound of bodyweight.
Why is the macronutrient so important? Protein and its amino acids are the primary building blocks for your muscles and bones, and are crucial for healthy hormone production. The skepticism about high-protein diets comes from the question of how your body processes the excessive nutrients and potentially dangerous amino acids, like nitrogen.
Check out whether these five commonly spouted risks are actually fact or fiction.
The rumored risk: The more protein you ingest, the more you’ll bulk up
The verdict: Muscle protein synthesis—or your body's ability to take protein’s amino acids and turn them into muscle—caps at 30g of the macronutrient, says Nancy Rodriguez, Ph.D., R.D., director of the University of Connecticut’s Sports Nutrition program. That means that downing a 50-g protein shake will have the same effect on muscle growth as downing a 30-g shake. In fact, a 2014 study in the Journal of the International Society of Sports Nutrition found that strength trainers who consumed 5.5 times the recommended daily protein (that’s just over 2g per pound of bodyweight) saw no positive or negative effect on body composition. In other words, you’re not putting your muscles at risk—but you are wasting precious protein powder.
The rumored risk: Excess protein gets stored as fat, in turn making you fat
The verdict: "The body has the ability to process the protein it consumes in a variety of ways," explains Rodriguez. When you digest and absorb more than your body can use for muscle protein synthesis, the surplus is most often used as a fuel source. The body is actually not very efficient at making fat from protein, she adds.
Science agrees: A 2009 study in The Journal of Nutrition revealed that people who followed a high-protein diet lost more body fat and had better blood lipid profiles than those who followed the USDA's Food Guide Pyramid, which is rich in carbs. That’s because protein makes you far more satiated than carbohydrates, so you’re snacking less throughout the day, and focusing on upping protein means you’re probably cutting refined carbs, even unintentionally.
However, if your high-protein diet is from loads of fatty meats, that can cause you to gain weight, says David Heber, M.D., Ph.D., founding director of the UCLA Center for Human Nutrition and author of LA Shape Diet. “A typical prime rib is about 1,500 calories. In fact, red meats are often the only way large men can remain obese," he adds.
The rumored risk: Too much protein causes the kidneys to work on overdrive and can actually cause kidney failure
The verdict: A study in Nutrition & Metabolism found that unless you have kidney disease, too much of the macronutrient won't have any kind of detrimental effect on kidney function. However, the source of your protein does matter. “The kidneys have to dispose of organic acids from animal protein but not plant protein, so limit animal meats and products to no more than 50% of your protein sources,” Heber advises.
The rumored risk: Eating a high-protein diet increases your risk of certain diseases and early death
The verdict: This idea is based upon, among other research, a 2014 study in Cell Metabolism that found middle-aged folks who ate a high-protein diet were more likely to die of cancer—at a rate comparable to smokers, in fact—than those who limited their intake. What’s more, the high-protein people were 75% more likely to die of any cause than those who skimped on the stuff.
However, these results were only in the folks who ate a diet rich in animal protein specifically. The risk almost vanished when the researchers honed in on participants whose protein mainly came from plants, such as beans. And that’s one of the biggest mistakes, says Heber—to consider the protein content of a food and not the other macro- and micronutrients involved. And since processed meats have now officially been USDA-deemed carcinogenic and red meats flagged as very likely to be the same, your best bet to score protein and avoid any detrimental side effects is to try and stick to lean meats (like chicken and turkey) and complete plant-based protein, like soy, beans and rice, and quinoa.
The rumored risk: A high-protein diet increases your risk of osteoporosis
The verdict: Your bones are safe, even with an influx of the nutrient. What’s more, underdoing it may be detrimental to them. A 2011 paper in Current Opinion in Lipidology looked at key epidemiological and clinical trials, and found that dietary protein actually works synergistically with calcium to improve retention as well as how much new, healthy tissue is formed. Neither of these are compromised by excess protein but are compromised with insufficient amounts.