Packing in the protein is all the rage. From cereal to pasta to nacho chips and more, food manufacturers are trying to get as much of the stuff into their products as possible, and one of the benefits they tout is that protein increases muscle mass and strength.

That might catch the attention of older adults. Strength inevitably declines with age, and that can come with severe consequences, from falling to losing the ability to live independently.

But older adults can probably skip the protein-boosted milk in their next Starbucks latte, because a recent study from Tufts University published in the American Journal of Clinical Nutrition shows that protein alone doesn’t equate to muscle strength.

In fact, as long as they’re getting the normal recommended amount of protein in their diets to begin with (as most older people in the U.S. do), older adults are better off hitting the gym if they want to keep their muscles youthful, said lead author and endocrinologist Lisa Ceglia, an associate professor at Tufts University School of Medicine and a postdoctoral fellow at the Jean Mayer USDA Human Nutrition Center on Research Center on Aging (HNRCA), who worked on the study with colleagues including HNRCA Senior Scientist and School of Medicine Professor Bess Dawson-Hughes.

A slow decline

The slow decline of muscle strength starts around age 40, when the kidneys begin to lose the ability to excrete acid from the body effectively. The body starts breaking down muscle to release basic substances that neutralize the acid, like baking soda neutralizes vinegar.

Past studies have come tantalizingly close to showing that adding protein to an older person’s diet can curb muscle loss — they’ve shown that it increases the growth factors that kickstart the process, and that protein in conjunction with exercise builds strength.

But until recently, scientists had stopped short of rigorously testing whether extra protein alone can limit muscle loss in a person who’s healthy and well nourished. “So then you start to say, yes, in theory this makes a lot of sense, but let’s look at the reality,” Ceglia said.

To test the benefits of protein alone, she and her collaborators recruited 141 study participants—all people aged 65 and above from the greater Boston area—and assigned some of them to take capsules containing whey powder while others took a placebo control. Made from milk, whey is rich in an amino acid called leucine, which is particularly good at jumpstarting the cellular pathways that build muscle. Other types of protein supplements (such as soy) might have different effects, but the researchers deemed whey the most likely to lead to muscle growth.

Along with whey powder, the researchers gave participants potassium bicarbonate, a component of antacid tablets. If acid build-up was the reason for loss of strength, they figured neutralizing the acid via the potassium bicarbonate could let muscles recover. Smaller studies had suggested they might be right.

After 24 weeks, the researchers tested the study participants’ strength with a range of exercises, from leg presses to a balance test. The results were unexpected: Participants’ strength was unchanged by the extra protein, with or without potassium bicarbonate. Those results were the same regardless of participants’ sex.

“We were surprised,” Ceglia said, especially because tests revealed that the participants’ bodies were primed to make more muscle. They excreted more acid, as a younger person would, and they had elevated levels of a muscle building hormone called IGF-1.

Open questions

So why didn’t they build more muscle? “This is an excellent question, and one that I’ve been asking myself,” Ceglia said. It’s possible that the study participants’ muscles were undergoing subtle changes that the strength tests weren’t sensitive enough to pick up. It’s also possible that without added exercise, participants’ bodies didn’t know what to do with the extra protein.

People who’ve recently added more exercise into their routines might benefit from protein supplementation. Other groups, such as those who become malnourished after serious injuries like hip fractures, may benefit too. This is why the protein-rich drink Boost is sometimes prescribed to people who have poor appetite after surgery.

“But if you’re just a healthy individual living in the community and eating protein at the recommended daily amount, there’s no evidence that protein supplementation alone will have a huge impact on your strength and function,” Ceglia said.

In the future, Ceglia would like to investigate the combination of exercise and protein supplementation to see if the two together are more effective than exercise alone. Until then, she recommends that older people use resistance training to keep their strength up. “It’s the most consistently effective option we have for improving strength and function,” she said.