Whether you’re trying to lose weight, gain muscle or stay strong and healthy as you age, protein is vital.
Protein is one of three macronutrients — along with carbohydrates and fat — that your body needs to build and repair tissue, form muscle and transport nutrients, says Erin Coates, a registered dietitian with Cleveland Clinic Wellness. Together, these macronutrients “are the building blocks of nutrition,” she says.
Registered dietitian Lora Edwards agrees, adding that protein is essential not just for our muscles, but also to develop and maintain healthy bones, skin and hair. She’s a senior clinical nutrition specialist at the Sports Medicine Center at Children’s Mercy Hospital in Kansas City, Missouri. “It’s also vital for our immunity and even makes up the hemoglobin that carries oxygen in your blood,” Edwards says.
Consuming enough protein is particularly important for older people, research suggests. Older adults who didn’t get enough protein “had significantly more functional limitations across all age groups,” according to a study of 11,680 people between ages 51 and up that was published online in February 2019 in the Journal of Nutrition, Health & Aging.
The importance of getting enough protein is clear. But how much protein is enough versus too much? The current recommended daily allowance for adults is 0.8 grams per kilogram of an individual’s body mass (or 0.36 grams per pound of body weight). However, over the past decade, researchers found that increasing protein intake is safe and can help minimize muscle loss when cutting calories while dieting, says Chad Kerksick, director of the Exercise and Performance Nutrition Laboratory at Lindenwood University in St. Charles, Missouri.
[See: 5 Unintended Consequences of Eating Too Much Protein.]
In 2015, a comprehensive review in Applied Physiology, Nutrition, and Metabolism concluded that consuming 25 to 35 grams of protein per meal was sufficient for most adults. However, some people, especially those trying to lose weight or gain muscle, as well as older adults, likely need more protein. The review found that for people trying to lose a substantial amount of weight, diets that included roughly 25% of their daily calories from protein helped prevent muscle loss and weight regain. For a person eating 1,600 calories per day, that would equal 100 daily grams of protein. The latest broad sports nutrition review that studied protein needs, published in 2018 in the Journal of the International Society of Sports Nutrition, concluded that, at a minimum, people need to double the recommended daily allowance to effectively build muscle. People who are trying to build muscle mass or who want to lose body fat should minimally eat about 1.6 grams of protein per kilogram of body weight. For a 150-pound person (who weighs 66.6 kilograms), that would equal 106 grams of protein daily, says Colin Wilborn, the executive dean for the Mayborn College of Health Sciences at the University of Mary Hardin-Baylor in Belton, Texas. Wilborn is a co-author of the 2018 sports nutrition review.
How protein intake impacts kidney function
Meanwhile, other experts have warned that consuming more than 20 grams of protein in a single sitting would turn protein to fat. Even worse, some experts have warned that excess protein intake can cause serious and potentially fatal damage to the kidneys.
Your body will use “however much (protein) you eat — whether that’s 50 grams or 250 grams,” says Donald K. Layman, professor emeritus in the department of food science and human nutrition at the University of Illinois.
“(For) forever, people have tried to make it about kidney function,” Layman says. Researchers have debunked the myth that in healthy adults, high protein intake negatively affects the kidneys, he explains.
Every time you eat protein, the liver converts its nitrogen into the compound urea, which the kidneys then process and allow you to excrete from your body through urine, he says. “Urea production is very healthy and normal,” Kerksick says. “It’s a natural byproduct of nitrogen metabolism. When you consume more protein, you just produce a little more of it.”
However, in those with urea cycle disorder, the liver doesn’t properly process the nitrogen, allowing it to build up in the blood as ammonia. Heightened levels of ammonia in the blood can contribute to everything from fatigue to death. According to the National Urea Cycle Disorders Foundation, 1 in 8,500 babies are born with urea cycle disorder, and it, along with other metabolic disorders, may account for up to 20% of sudden infant death syndrome, so it’s an extremely rare condition among adults.
It’s unusual that people would consume too much protein strictly from eating food, says Katie Kissane, a registered dietitian at UCHealth Poudre Valley Hospital in Fort Collins, Colorado. It’s more common for some people to consume an excessive amount of protein through supplements. “It’s hard for people to get too much protein from food, because protein is so satiating,” Kissane says. “You could get excessive amounts of protein from food, but you’re going to feel pretty full all the time.” Eating too much protein can also cause some people to not drink enough water or consume the proper amounts of high-fiber foods, like vegetables and fruits, because they feel so full, she says.
According to Kate Patton, lead outpatient dietitian at Cleveland Clinic, here are four potential signs that you’re consuming too much protein:
— A constant feeling of fullness.
— Indigestion.
— Constipation.
— Dehydration.
[See: These Healthy Seasonings Are Tasty Substitutes for Sugar and Salt.]
How much protein your body needs
Your body will use “however much (protein) you eat — whether that’s 50 grams or 250 grams,” Layman says.
The only difference is how your body uses protein, Layman says. The body can only use so many amino acids (the building blocks of protein) for muscle protein synthesis, the process by which muscle cells repair and grow, he says. And muscle health and growth is the primary reason that people consciously increase their protein intake.
Exactly how much protein the body can use toward muscle-building depends on a multitude of factors, including body size, physical activity level, age, total calorie intake and health, explains board-certified sports dietitian and registered dietitian Marie Spano, co-editor of the National Strength and Conditioning Association’s “Guide to Sport and Exercise Nutrition.” People who are larger and more active have greater protein requirements, as do those who are in a caloric deficit and want to prevent the body from breaking down existing muscle tissue for energy. Plus, after about the first 25 to 30 years of life, people naturally become less efficient at using the amino acids from protein to build muscle, meaning they need to eat more to get the same effect, Layman says.
To determine an individual’s ideal protein intake, the efficiency at which the body uses protein is an important consideration. Why? When it comes to absorbing and using protein to build tissue, muscle cells don’t operate like an on/off switch. Instead, they act more like a dimmer, where, at a certain point, they gradually become less efficient at using each amino acid to build muscle tissue.
“You need a certain amount for protein to be effective at triggering muscle protein synthesis, and there is an increasing effect up to a certain point, but then the effect of each additional gram starts decreasing,” he says. “So, for example, you might get 90% of maximum efficiency with 25 to 30 grams, but then start to have decreasing efficiency after 50 grams.”
A 2018 review published in the Journal of the International Society of Sports Nutrition concluded that in order to maximize muscle-building, people should eat between 0.4 and 0.55 grams per kilogram of their body mass at least four times per day. For a 180-pound adult, that recommendation works out to four meals of 33 to 45 grams of protein at each meal.
[See: 14 Things You Shouldn’t Say to Someone Who’s Trying to Lose Weight.]
What happens to protein that isn’t used to build muscle
“We mostly talk about dietary protein in regard to muscle protein synthesis, but there are trillions of cells in the body that require protein,” Kerksick says. “It is needed for the healthy cell turnover and recovery in the organs, tissues — all of the cells within the immune system require protein.” Basically, muscle aside, protein serves as a primary structural component throughout the body, allowing even the most basic of physiological functions.
That means that whenever you eat protein, some amino acids are stored in what is called an amino acid “pool,” Wilborn says. These pools are used for protein synthesis, which contributes to the health and maintenance of muscles and cardiovascular and neurological systems throughout the body.
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How Much Protein Do I Need? originally appeared on usnews.com
Update 08/29/19: This article was previously published on an earlier date and has been updated with new information.
Correction 08/30/19: A previous version of this story misquoted Erin Coates’ description of macronutrients.
