Can You Get Too Much Protein?
Protein has achieved a venerated status in the dietary world for everything from building muscle to preventing weight gain. But can you get too much of a good thing?
Protein powders that come in chocolate, strawberry, and cookies and cream flavors are doled out by the scoopful and mixed into smoothies, making it possible to effortlessly consume protein in amounts that far exceed dietary recommendations. A canned protein drink can contain almost as much protein as an eight-ounce steak, and snack bars or a small bag of protein chips can pack more of the macronutrient than a three-egg omelet.
But while some nutritionists have encouraged the protein craze, a number of experts are urging caution. They point out that protein powders and supplements, which come from animal products like whey and casein (byproducts of cheese manufacturing) or from plants like soy, rice, pea or hemp, are a relatively new invention. The vast majority of Americans already get more than the recommended daily amounts of protein from food, they say, and there are no rigorous long-term studies to tell us how much protein is too much.
“It’s an experiment,” said Dr. John E. Swartzberg, chairman of the editorial board of the University of California, Berkeley, Wellness Letter. “No one can tell you the long-term effects, and that’s what worries me as a physician. No one can tell you what the results are going to be in people’s bodies 10 or 15 years later.”
People need sufficient protein in the diet because it supplies indispensable amino acids that our bodies cannot synthesize on their own. Together they provide the essential building blocks used to make and maintain muscle, bone, skin and other tissues and an array of vital hormones and enzymes.
But the average adult can achieve the recommended intake — 46 grams of protein a day for women, and 56 grams for men — by eating moderate amounts of protein-rich foods like meat, fish, dairy products, beans or nuts every day. There are about 44 grams of protein in a cup of chopped chicken, 20 grams in a cup of tofu or serving of Greek yogurt, and 18 grams in a cup of lentils or three eggs.
American men already consume much greater amounts, averaging nearly 100 grams of protein a day, according to a 2015 analysis of the 2007-2010 National Health and Nutrition Examination Survey. The revised Dietary Guidelines for Americans, released in January, cautioned that some people, especially teenage boys and adult men, should “reduce overall intake of protein foods” and eat more vegetables.
Among the groups that fall short on protein intake are teenage girls, who may not eat properly, and elderly people, who are at risk of losing muscle mass and whose appetites often slacken with age. Indeed, many of the earliest nutritional supplement products, like Boost and Ensure, were devised with the elderly and malnourished in mind. (Professional athletes who work out many hours a day also need to increase protein intake considerably, as do women who are pregnant or breast-feeding.)
Yet the protein supplement market is booming among the young and healthy, with retail sales of sports nutrition protein powders and other products in the United States alone projected to reach $9 billion by 2020, up from about $6.6 billion last year, according to the research firm Euromonitor International.
“People think carbs are the enemy, protein is your friend,” said Eleanor Dwyer, a research analyst with the firm, and “that any health concerns are overblown.”
Experts note, however, that there is only so much protein the body can use. “The body only digests and absorbs a certain amount of protein at every meal,” about 20 to 40 grams, said Jim White, a registered dietitian and exercise physiologist who spoke on behalf of the Academy of Nutrition and Dietetics. “People think that if they fill up with protein, it will be a magic bullet, whether for weight loss or to get in better shape and build muscle — but that’s not proving to be true.”
“You can eat 300 grams of protein a day, but that doesn’t mean you’ll put on more muscle than someone who takes in 120 grams a day,” Mr. White said. Meanwhile, “you’re robbing yourself of other macronutrients that the body needs, like whole grains, fats, and fruits and vegetables.”
Short-term studies suggest that high protein, low carbohydrate diets may promote weight loss and help to preserve lean muscle, and that eating protein helps satisfy hunger. But a recent small trial found that older women who lost weight on a high protein diet did not experience one of the important benefits that usually follow weight loss, an improvement in insulin sensitivity, which reduces the risk of developing Type 2 diabetes. Large population studies also suggest an association between habitual high protein intake and a heightened risk of diabetes.
Doctors also have concerns about the long-term effects of maintaining a high protein diet. Studies show that protein-rich diets do not preserve muscle mass over the long term, and doctors have long cautioned that a high-protein diet can lead to kidney damage in those who harbor silent kidney disease by putting extra strain on the kidneys. Up to one in three Americans are at risk for kidney impairment because of high blood pressure or diabetes, according to the National Kidney Foundation.
Furthermore, some researchers worry that the muscle building properties that consumers seek in protein may be a double-edged sword, perhaps even leading to an increased risk of cancer.
“One of the benefits and concerns about high protein intake, especially animal protein, is that it tends to make cells multiply faster,” said Dr. Walter Willett, chairman of the department of nutrition at the Harvard T. H. Chan School of Public Health. “That’s good in early life, when you’re a growing child. But in later life, this is one of the fundamental processes that increase the risk of cancer.”
Several large observational studies have linked high-protein diets with an increased incidence of cancer, heart disease and other ills. One study led by Valter Longo, the director of the Longevity Institute at the University of Southern California in Los Angeles, followed a nationally representative sample of 6,381 adults. It found that those who ate a high protein diet between the ages of 50 and 65 were four times more likely to die of cancer than those who consumed less protein.
By eating large amounts of protein several times a day, “you’re generating a very novel environment that the body has never seen before,” said Dr. Longo, the founder of a company called L-Nutra that makes foods for healthy aging. “Even if you went back to a time when people ate a lot of meat, they would not have had pure proteins being fed multiple times a day.” He added that most of our early ancestors did not live past age 50.
Skeptics dismiss these concerns as speculative, saying they are not supported by adequate evidence. And some nutritionists advise adults to consume twice as much protein as currently recommended.
“There is a distinction between what is absolutely minimally required and a more optimal intake level,” said Stuart M. Phillips, a professor of kinesiology at McMaster University in Hamilton, Ontario, whose research has been supported by trade groups like the National Dairy Council and the National Cattlemen’s Beef Association. He advises adults to eat 30 to 40 grams of protein at every meal to help alleviate the loss of muscle that can occur with aging.
Where you get your protein is also important. Consumer groups have warned about the potential contamination of protein products, which are categorized as dietary supplements and loosely regulated. A Consumer Reports test of 15 protein powders and drinks in 2010, for example, found arsenic, lead, cadmium and mercury in some of the products tested.
Duffy MacKay, the senior vice president for scientific and regulatory affairs at the Council for Responsible Nutrition, an industry group that represents supplement manufacturers, dismissed concerns about toxic substances as “a lot of smoke.”
“These are all made from naturally derived materials that come from plants and animals, and in any naturally derived materials there are going to be trace amounts of environmental chemicals,” Mr. MacKay said.
But Mr. White, like many dietitians, said he recommended eating whole foods, rather than supplements. If you’re looking for alternatives to raise your smoothie’s protein content, for example, he suggested protein-rich foods like yogurt and peanut butter.