According to Gram Research analysis, older adults can build muscle on a vegetarian diet when eating adequate protein and doing strength training, though they may gain slightly less muscle than meat eaters. In a 12-week study of 108 adults aged 55 and older, vegetarians gained 0.38 kilograms of muscle while omnivores gained 0.66 kilograms. Both groups improved strength and function similarly, suggesting that getting enough total protein matters more than its source.
A new study followed 108 older adults for 12 weeks to see if vegetarians could build muscle as well as meat eaters when doing strength training. Both groups ate enough protein and did the same exercises three times a week. The vegetarian group ate slightly less protein overall, but both groups successfully gained muscle and got stronger. The research shows that older adults can build muscle on a plant-based diet, though meat eaters gained a bit more muscle mass in this particular study.
Key Statistics
A 2026 randomized controlled trial of 108 older adults found that vegetarians gained 0.38 kilograms of muscle over 12 weeks of resistance training, compared to 0.66 kilograms for meat eaters, when both groups consumed at least 1.2 grams of protein per kilogram of body weight daily.
In the same study, the vegetarian group consumed an average of 1.24 grams of protein per kilogram of body weight daily from predominantly plant sources, while the omnivorous group consumed 1.58 grams daily from predominantly animal sources.
Both the vegetarian and omnivorous groups showed significant improvements in leg press strength and chair stand test performance over 12 weeks, with no meaningful differences between groups despite the difference in muscle mass gains.
The vegetarian group achieved 76% of their daily protein intake from plant-based sources, while the omnivorous group achieved 67% from animal-based sources, demonstrating successful adherence to their assigned dietary patterns.
The Quick Take
- What they studied: Whether older adults eating a plant-based vegetarian diet could build as much muscle as those eating meat when both groups did strength training exercises.
- Who participated: 108 adults aged 55 and older (average age 66, about 58% women) with normal to slightly overweight body sizes. Half followed a vegetarian diet and half ate meat.
- Key finding: Both groups gained muscle and got stronger over 12 weeks, but the vegetarian group gained slightly less muscle (0.38 kg) compared to the meat-eating group (0.66 kg). The vegetarian group also ate less total protein per day.
- What it means for you: Older adults can successfully build muscle on a plant-based diet when they eat enough protein and do strength training, though they may need to be more intentional about getting adequate protein compared to meat eaters.
The Research Details
This was a randomized controlled trial, which is one of the strongest types of research studies. Researchers randomly assigned 108 older adults to either a vegetarian diet group or an omnivorous (meat-eating) diet group. Both groups received nutrition counseling to help them eat enough protein, specifically aiming for at least 1.2 grams of protein per kilogram of body weight daily. The vegetarian group focused on getting 60% or more of their protein from plant sources like beans, nuts, and dairy, while the meat-eating group aimed for 60% or more from animal sources. All participants completed the same 12-week strength training program, exercising three times per week. Researchers measured muscle mass using a special scanning machine called a DXA scan, tested leg strength, and tracked how much protein each person actually ate using food records.
This study design is important because it controls for exercise and overall protein intake, allowing researchers to isolate the effect of the protein source itself. By randomly assigning people to groups, the study reduces bias and makes the results more reliable. The 12-week duration is long enough to see real changes in muscle but short enough to maintain good participation rates.
This is a well-designed study published in a top nutrition journal. The researchers used objective measurements like DXA scans instead of relying on self-reported muscle mass. They tracked actual food intake with food records. The study had a clear protocol registered before it started. However, the study was relatively small with only 108 participants, and it only lasted 12 weeks, so longer-term effects are unknown.
What the Results Show
Both groups successfully increased their muscle mass during the 12-week study. The vegetarian group gained an average of 0.38 kilograms of muscle, while the omnivorous group gained 0.66 kilograms. Both improvements were statistically significant, meaning they were real changes and not due to chance. However, the vegetarian group gained about 0.33 kilograms less muscle than the omnivorous group, which was larger than the study’s threshold for considering the diets equivalent. The vegetarian group ate an average of 1.24 grams of protein per kilogram of body weight daily, while the omnivorous group ate 1.58 grams per kilogram daily. This difference of 0.34 grams per kilogram was statistically significant. Both groups successfully met their protein intake targets and achieved their intended protein sources, with the vegetarian group getting 76% of protein from plants and the omnivorous group getting 67% from animals.
Both groups showed significant improvements in leg press strength and the ability to stand up from a chair repeatedly, with no meaningful differences between groups. Handgrip strength improved in both groups as well. These results suggest that the functional strength gains from resistance training were similar regardless of diet type, even though total muscle mass gains differed slightly.
This study aligns with previous research showing that plant-based diets can support muscle building in older adults when protein intake is adequate. However, it adds new evidence that omnivorous diets may provide a slight advantage for muscle gain in this age group. The finding that both groups improved strength and function despite different muscle mass gains suggests that protein source matters less than total protein intake for functional outcomes.
The study only lasted 12 weeks, so we don’t know if these differences persist over months or years. The sample size of 108 people is relatively small, which limits how broadly we can apply the findings. The study included mostly healthy, motivated older adults who were willing to follow dietary counseling, so results may not apply to less healthy populations. The study didn’t measure other important factors like bone health or cardiovascular benefits. Participants self-selected their foods, which means some may have followed the diet better than others.
The Bottom Line
Older adults following a vegetarian diet can build muscle and improve strength during resistance training if they eat at least 1.2 grams of protein per kilogram of body weight daily. This is a moderate confidence recommendation based on this single 12-week study. Omnivorous diets may provide a slight advantage for muscle gain, but both approaches work. Strength training three times per week appears essential for muscle building in both groups.
This research is most relevant to older adults (55+) considering a vegetarian diet who want to maintain or build muscle. It’s also useful for vegetarians concerned about protein intake during aging. People with certain medical conditions, those taking medications that affect muscle, or those unable to do resistance training should consult their doctor before making dietary changes.
Participants in this study saw measurable muscle gains within 12 weeks. However, the gains were modest (less than 1 kilogram), so realistic expectations are important. Strength improvements appeared alongside muscle gains, suggesting functional benefits may appear within weeks even if muscle mass changes take longer.
Frequently Asked Questions
Can vegetarians build muscle as well as meat eaters when exercising?
Vegetarians can build muscle effectively when eating enough protein and doing strength training, though research shows they may gain slightly less muscle than meat eaters. A 2026 study found vegetarians gained 0.38 kg of muscle versus 0.66 kg for omnivores over 12 weeks, but both groups improved strength similarly.
How much protein do older vegetarians need to build muscle?
Older vegetarians should aim for at least 1.2 grams of protein per kilogram of body weight daily. For a 70-kilogram person, that’s about 84 grams daily. The study showed this amount supported muscle building when combined with regular strength training.
Does it matter if protein comes from plants or animals for muscle building?
Total protein intake appears more important than the source for building muscle and improving strength in older adults. The study showed both plant-based and animal-based protein diets produced similar strength gains, though omnivorous diets resulted in slightly more muscle mass.
How often should older adults do strength training to build muscle?
The study used three strength training sessions per week over 12 weeks and found this frequency produced measurable muscle gains and strength improvements in both vegetarian and omnivorous groups. This appears to be an effective frequency for older adults.
Can plant-based protein sources like beans and nuts build muscle?
Yes, plant-based proteins can support muscle building. In the study, vegetarians got 76% of their protein from plant sources like beans, nuts, seeds, and dairy, and successfully gained muscle and improved strength when total protein intake was adequate.
Want to Apply This Research?
- Track daily protein intake in grams and compare it to your target of 1.2 grams per kilogram of body weight. For example, a 70-kilogram person should aim for 84 grams daily. Log protein sources separately to monitor plant versus animal ratios.
- If following a vegetarian diet, use the app to identify high-protein plant foods you enjoy (beans, lentils, tofu, nuts, seeds, dairy if lacto-ovo) and plan meals around these. Set reminders for strength training sessions three times weekly, as the study shows this frequency is important for muscle building.
- Measure progress every 4 weeks by tracking strength improvements in your workouts (how much weight you can lift or how many repetitions you can do) rather than relying solely on the scale. Take body measurements or progress photos monthly, as muscle gain may not always show on a scale if fat loss occurs simultaneously.
This research applies specifically to healthy older adults aged 55 and older who are able to participate in resistance training. Individual results may vary based on genetics, overall health, medications, and exercise adherence. Older adults with chronic conditions, those taking medications affecting muscle metabolism, or anyone new to exercise should consult their healthcare provider or a registered dietitian before making significant dietary changes or starting a new exercise program. This article summarizes research findings and should not be considered medical advice.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.