“We’re constantly making and breaking down muscle,” explains physiologist Jared Dickinson, of Arizona State University. “Between meals we have a higher rate of breakdown, and then after meals a higher rate of synthesis.”
But “older adults may not make enough muscle after meals to fully overcome the breakdown in muscle they experience between meals,” adds Dickinson. “So, over the course of a day, a month, a year, older people may experience a net loss of muscle.” (Some of Dickinson’s research has been funded by General Mills and by a soy protein manufacturer, as well as by NIH.)
Can eating more protein help prevent muscle loss? It’s not clear.
The evidence that older people make less muscle after meals than younger people comes mostly from small studies that lasted just a few hours.
For example, when 11 older adults got the amino acids in 15 grams of protein, they incorporated less of them into muscle—at least over the next 3½ hours— than did eight younger adults. (You’d get 15 grams of protein in two ounces of meat, chicken, or fish, or six ounces of greek yogurt.)
But with more than 15 grams, the difference between older and younger seemed to disappear. For example, Dutch researchers found that 12 older men incorporated just as much protein into muscle as 12 younger men within six hours after they were all given 20 grams of protein. And U.S. researchers found the same after they gave six younger and seven older people 30 grams of protein.
“Those studies only measured synthesis, not breakdown, so we don’t know what the net impact on protein balance is over time,” cautions researcher Wayne Campbell, a professor of nutrition science at Purdue University. (Some of Campbell’s research has been funded by the beef, pork, dairy, and egg industries, as well as by NIH.)
How much protein you get at each meal may also matter. For one week, researchers fed eight people aged 25 to 55 a diet that contained 90 grams of protein a day: a low-protein breakfast (11 grams), a low-protein lunch (16 grams), and a protein-heavy dinner (63 grams). During another week, the same people were fed roughly 30 grams of protein at each meal.
“Total muscle protein synthesis was about 25 percent greater when the participants ate meals that had evenly distributed protein,” says co-author Doug Paddon- Jones, a physiologist at the University of Texas Medical Branch at Galveston. (Some of Paddon-Jones’ research has been funded by the beef and dairy industries, as well as by NIH.)
“It’s a very small initial study,” he cautions, “and we didn’t have anyone older than 55 participating in it.”
What’s more, in an earlier study by Paddon-Jones, people made no more muscle protein after eating 90 grams of protein than after eating 30 grams. That may explain why people who got 30 grams of protein at each meal made more muscle than those who got just 11 grams at breakfast (less than 30), 16 grams at lunch (less than 30), and 63 grams at supper (no better than 30).
“Evenly distributing sufficient protein throughout the day is an intriguing concept,” says Campbell. “But we don’t know yet how significant it is and whether a short-term effect leads to actual changes in muscle or physical function or anything else related to people’s well-being.”
And in long-term studies, it’s not clear that getting extra protein for months preserves muscle.
When Campbell fed 10 people aged 54 to 78 the RDA for protein—0.36 grams per pound of body weight—for 12 weeks, they lost thigh muscle. But so far, few studies have tested whether more protein than the RDA (without exercise) prevents muscle loss or builds muscle.
And some results aren’t easy to interpret. For example, researchers gave 65 frail elderly people (average age: 80) an extra 15 grams of protein or a placebo at breakfast and again at lunch every day. After six months, the protein eaters had no greater muscle mass or strength, but they did have a better “physical performance” score. (They could stand up more quickly and lift more with their legs.)
What is clear: the best way to build muscle is to do strength training.
“The science is pretty sound that strength training definitely works more robustly than the effects of protein,” says Campbell. In fact, in many studies, extra protein plus strength training built no more muscle than strength training alone.
For example, when Campbell had 220 overweight or obese middle-aged men and women do nine months of strength training twice a week and aerobic exercise once a week, they gained strength and lean muscle. But those who also were given 20, 40, or 60 grams of whey protein every day were no stronger and gained no more muscle than those who took a placebo.
Similarly, when other researchers had 80 adults aged 70 to 85 do strength training and take either a placebo or whey protein (40 grams a day) for six months, the whey made no difference in muscle strength or size.
However, a Dutch study got mixed results. After six months of strength training, frail elderly people gained leg strength and were able to get up out of a chair faster than when they entered the study. But those who were given an extra 15 grams of protein at breakfast and lunch during the six months did no better than those who got a placebo. The group that got extra protein did gain more muscle mass, however.
Campbell’s bottom line: “It’s wonderful marketing for companies that would like to sell high-protein breakfasts and lunches and the like, but the science on whether or not protein actually has an impact on a person’s body composition or skeletal muscle, size, strength, function—we’re still doing the research.”
Until the evidence becomes clear, how much protein should you eat?
“Make sure you don’t slide below the amount of protein that the average older person consumes,” says Campbell. “That’s what the two expert panels concluded.”
That means shooting for 0.5 grams of protein for every pound you weigh.
“If you’re trying to lose weight by eating fewer calories,” adds Campbell, “make sure you’re cutting carbohydrates and fats, not protein.”
Others suggest that if you’re older and have trouble eating enough protein—and enough food—try a protein drink.
“As we age, our appetite and satiety cues are blunted,” explains Heather Leidy, a nutritional physiologist at the University of Missouri. “When you drink protein in a shake or smoothie, you don’t get the same feeling of satiety or fullness that you would if you ate your protein as a solid food. So that’s an excellent strategy for folks who need to get a certain amount of protein without reaching a level of fullness that stops them from eating throughout the day.”
(Some of Leidy’s research has been funded by the beef, pork, egg, and dairy industries, General Mills, and a soy protein manufacturer, as well as by NIH.)
Sources: Am. J. Clin. Nutr. 82: 1065, 2005; Am. J. Clin. Nutr. 93: 322, 2011; Am. J. Physiol. Endocrinol. Metab. 286: E321, 2004; J. Nutr. 144: 876, 2014; J. Am. Diet. Assoc. 109: 1582, 2009; J. Physiol. 542(Pt 2): 631, 2002; JAMDA 13: 720, 2012; J. Nutr. 142: 1532, 2012; J. Gerontol. A Biol. Sci. Med. Sci. 68: 682, 2013; JAMDA 13: 713, 2012; Horm. Metab. Res. 39: 389, 2007.
Other relevant links:
- Consuming extra protein may help dieters. See: Diet and Weight Loss: Can Eating More Protein Help You Lose Weight?
- Should you consume protein drinks to help with your appetite? See: Do Protein Drinks Really Curb Your Appetite?
- Aging and muscle maintenance. See: How to Maintain and Build Muscle