Can Older Vegetarians Build Muscle With Strength Training?

Can older vegetarians build muscle with strength training?

Yes. In a 12-week randomized trial of adults 55 and older, vegetarians who lifted weights gained 0.38 kg of arm and leg muscle, while meat eaters gained 0.66 kg. Both groups improved on the leg press and the chair-stand test, with no difference between them. The vegetarians ate less protein, and that gap is a likely reason they built less muscle.

Muscle loss with age is one of the biggest threats to independence later in life. Strength training is the best tool we have against it, and protein is the raw material muscle is built from. A mostly plant-based diet may lower the risk of chronic disease, but it can also mean less protein. This trial, called IMPACT, asked whether older vegetarians who lift weights can keep up with older meat eaters who do the same program.

What the data show

The researchers randomly assigned 108 adults with a median age of 66 to one of two diets. One group ate a lacto-ovo vegetarian diet, which allows dairy and eggs but no meat or fish. The other group ate an omnivorous diet. Everyone chose their own foods, got dietary counseling, and aimed for at least 1.2 grams of protein per kilogram of body weight per day. All of them did the same 12-week strength program, three sessions a week.

Both groups hit their protein target. The vegetarians averaged 1.24 g/kg/day, with 76% of it from plants. The omnivores averaged 1.58 g/kg/day, with 67% from animal foods. For a 70 kg (154 lb) person, that works out to about 87 grams versus 111 grams of protein a day.

Muscle in the arms and legs, measured with a DXA body scan, rose in both groups. The vegetarian gain of 0.38 kg had about a 4 in 1,000 chance of being a fluke (p = 0.004). The omnivore gain of 0.66 kg had less than a 1 in 1,000 chance (p < 0.001). Leg press strength and chair-stand performance improved in both groups, with no difference between them.

How strong is the evidence?

This was a “non-inferiority” trial. That design asks a specific question: is the vegetarian diet no worse than the omnivorous one, within a set margin? For muscle, the margin was 0.25 kg. For protein, it was 0.12 g/kg/day.

The vegetarian diet failed both tests. Vegetarians ate 0.33 g/kg/day less protein, and the true gap is very likely between 0.17 and 0.49 g/kg/day less. After the researchers’ analysis, the muscle gap was 0.33 kg in favor of the omnivores. Here the uncertainty is wide: the real difference could be as large as 0.69 kg or close to zero (95% CI -0.69 to 0.03). So the trial could not show that vegetarians keep pace on muscle, but it also could not prove they fall behind.

The strengths are real. It was randomized, everyone did the same training program, and muscle was measured by a scan rather than by tape or scale. The limits are real too. Twelve weeks is short, protein intake came from 3-day food records, and 108 people is a modest group for detecting small differences.

Dr. Kumar’s Take

The headline some people will write is “vegetarians can’t build muscle.” That is not what this trial shows. Vegetarians over 55 built muscle, got stronger, and improved their ability to stand up from a chair, which is one of the most practical measures of independence there is. On the strength and function tests, they matched the meat eaters.

What they did not match was protein intake. The omnivores ate about a quarter more protein, and they put on more muscle. Protein is the raw material for muscle, so a gap that size is a plausible reason for the difference.

The lesson for an older vegetarian is not to give up the diet. It is to take protein seriously. Hitting 1.2 g/kg/day was enough to build muscle in this trial. The omnivores went well past that target and gained more, and going higher takes planning on a plant-heavy diet.

Practical Takeaways

If you are over 55, start or keep a strength program, since both diet groups in this trial gained muscle and strength with three sessions a week for 12 weeks.
Calculate your own protein target by multiplying your weight in kilograms by 1.2, then track a few typical days to see whether you actually reach it.
If you eat vegetarian, lean on dairy and eggs as well as beans and lentils, because a lacto-ovo diet allows them and they make higher protein totals easier to reach.
Judge your progress by what you can do, such as rising from a chair or pushing more weight, since those gains were equal between the two diets.

FAQs

How much protein do older adults need to build muscle?

In this trial, both groups aimed for at least 1.2 grams of protein per kilogram of body weight per day, and both groups built muscle at that level. For a 60 kg (132 lb) person, 1.2 g/kg is 72 grams a day. The omnivore group ate more than the target, at 1.58 g/kg/day, and gained more muscle.

Is plant protein as good as animal protein for muscle?

This trial cannot fully answer that, because the two groups did not eat the same total amount of protein. The vegetarians ate 1.24 g/kg/day and the omnivores ate 1.58 g/kg/day. So the difference in muscle could come from the amount of protein, the source, or both. What the trial does show is that a diet getting 76% of its protein from plants still produced measurable muscle gain alongside strength training.

Does this apply to vegans?

Not directly. The vegetarian group ate a lacto-ovo diet, which includes dairy and eggs. Those foods make it easier to reach a high protein total. Vegans cut out those foods too, so this trial does not tell us how they would do. Anyone eating fully plant-based should expect that reaching the same protein target takes more planning.

Bottom Line

Older adults who lift weights three times a week can build muscle and strength on a vegetarian diet. In the IMPACT trial, vegetarians over 55 gained 0.38 kg of arm and leg muscle in 12 weeks, compared with 0.66 kg for meat eaters, with no difference between the groups in leg strength or chair-stand gains. The vegetarians ate less protein, and the diet did not meet the trial’s bar for being “just as good” on muscle. The practical message is simple: keep lifting, and if you skip meat, make hitting your protein target a deliberate goal.

Read the full study