It’s Time to Rethink High-Protein Diets for Weight Loss
A new study suggests there’s a downside to all that protein
Eating a diet that’s high in protein is often recommended for people trying to lose weight, since high-protein foodsmake people feel more full, preventing overeating. However, a new study suggests that while the diet may help people slim down, it doesn’t necessarily improve other health problems under the hood. (For more on that, see: How Much Protein Should I Eat Every Day.)
In a small study, researchers at Washington University School of Medicine in St. Louis followed 34 postmenopausal women with obesity for about six months. The women were split into three groups: One group kept their diet the same, one group went on a calorie-restricted weight loss diet (with the daily recommended amount of protein), and another group went on the same diet but also increased their protein intake by about 150-250 calories. The researchers provided all the meals for the women, and besides the increased protein, the diets were virtually the same.
The study authors found that while both groups of women were able to lose about 10% of their body weight, the women who ate more protein experienced no changes in their insulin sensitivity—which is important for overall health.
Improved insulin sensitivity is important to cut down on a person’s risk for type 2 diabetes—which is common in people with obesity. It’s one of the reasons weight loss is recommended for better health in the first place. The women who lost weight without increasing the amount of protein they ate experienced a 25 to 30% improvement in insulin sensitivity. But the women who ate more protein experienced no change in their insulin sensitivity at all. “We definitely expected a blunting of the effect, but to completely eliminate it was a little bit surprising,” says lead study author Bettina Mittendorfer, a professor of medicine.
The number of people in the study, which was published Tuesday in the journalCell Reports, is very small, but Mittendorfer says the report is not the first to raise skepticism about high-protein diets. “There is a reported association from epidemiological studies between protein intake and an increased risk for type 2 diabetes,” she says.
Mittendorfer and her fellow researchers plan to continue studying the issue to better understand why people who eat more protein did not experience the same metabolic benefits, and whether the type of protein a person consumes matters. For instance, does plant protein have different effects compared to animal protein? “It’s a tremendous effort to go through a 10% loss in body weight. To not see an improvement in one of these key factors is significant I think,” says Mittendorfer.
Though the study is small and more research is needed to better understand the findings, Mittendorfer says she would advise people to be “cautious” about adopting a high-protein diet to lose weight. “I think there is no reason to go for high protein intake during weight loss, based on our results,” she says. “There’s no reason to do it, and potentially there is harm or lack of a benefit.”
You Asked: How Much Protein Should I Eat Every Day?
That depends on a lot of factors, including your age
Dieting used to seem simple. If you were slim, you were in “good shape.” If you weren’t, losing a few pounds would benefit your health. But the latest research suggests that your risk for death and disease doesn’t always align with your physique. That makes pinpointing the “ideal” or “optimal” protein intake really tricky.
Some exercise researchers say more protein is often better—even in amounts well above the 56 grams a day (and 46 grams, for women)recommended by the Institute of Medicine (IOM). It’s filling, beneficial for appetite suppression and weight loss, and also helps prevent loss of muscle mass and strength as people age, says Dr. Stuart Phillips, a professor of kinesiology at Canada’s McMaster University. Animal sources of protein are also loaded with essential nutrients and amino acids—like iron and folate, which many people don’t get enough of, Phillips says.
For all these reasons, he says that adults, whether they’re sedentary or active, should consume a lot more protein than they probably do—up to .75 grams of protein per pound of body weight every day. For a 150-pound person, that works out to roughly the amount you’d find in a chicken breast or like-size cut of meat, a cup of beans, six ounces of Greek yogurt and eight ounces of milk, according to the USDA’s nutrient database.
But talk to a disease and longevity researcher, and you’ll get a very different answer—one that sure won’t please Paleo dieters.
“Proteins and their amino acids regulate the two major pro-aging pathways,” says Dr. Valter Longo, a professor of biological science at the University of Southern California. By “up-regulating” those pathways, eating lots of protein seems to promote higher rates of both death and disease, he says.
Longo’s research shows cancer rates increase nearly 400% among Americans who get 20% or more of their daily calories from protein, compared to those who restrict their protein intake to 10% of their daily calories. Risk of mortality also jumps 75% among the heavy protein eaters, his data show.
Of course, there are several important confounding factors baked into that data. Americans who eat lots of protein are probably getting it from unhealthy sources. But Longo says even if you cut out fatty, additive-stuffed cuts of meat—fast food burgers, breakfast sandwiches etc.—there’s still plenty of evidence to suggest protein consumption fuels disease and early death.
“We are not claiming that the high-protein diet cannot make you lose weight, but only that in the long run it is not healthy for you,” Longo says.
Based on his longevity research, he recommends people get no more than .37 grams of protein per pound of bodyweight—roughly half the amount Phillips recommends. For a 150-pound person, that works out to about 50 grams of protein daily.
But Phillips and Longo’s recommendations start to converge for older adults. For people over 65, muscle wasting and loss of strength become important concerns—so much so that eating more protein lowers your risk for both death and disease, Longo says. Once you hit 65, he says it’s fine to consume a bit more protein if you notice you’re starting to drop weight, lose strength or shed muscle mass.
All of this no doubt seems confusing and convoluted. (Despite what that bestselling diet book tells you, nothing is simple when it comes to your health and the food you eat.) But you can probably forget about counting protein grams if you do just one thing: adopt a Mediterranean-style diet.
Fish contains about half the protein found in chicken or red meat, and the other staples of the Mediterranean diet—olive oil, vegetables, whole grains and legumes—have low or modest amounts of it. That may be one reason why Mediterranean diets have repeatedly been linked to a longer life and lower rates of disease, Longo says—and it’s just one more reason to adopt the diet supported by research again and again.