A vegetarian diet can support substantial gains in muscle strength in older adults when combined with adequate protein intake and resistance exercise, according to a new clinical trial. Participants following vegetarian or omnivorous diets improved their strength and physical performance, with no statistically significant difference between the groups. However, the increase in muscle mass was greater in the omnivorous diet group.
The study was published in the American Journal of Clinical Nutrition and included 108 adults aged 55 and over. Participants were randomly assigned to two groups, which followed vegetarian or omnivorous diets for 12 weeks. All participants also did resistance training three times a week, with exercises such as leg and chest presses, squats, pull-ups and abdominal exercises.
Each participant received dietary guidance, with the goal of consuming at least 1.2 grams of protein per kilogram of body weight per day. On average, both groups met this target. The vegetarian diet excluded meat and fish but allowed dairy products, eggs and plant sources of protein. The findings therefore concern this dietary pattern and do not constitute a direct test of an entirely plant-based diet.
At the end of the intervention, both groups could lift more weight on the leg press and rise from a chair faster than at the start of the trial. Measurements showed improvements in both muscle strength and physical performance. The researchers at Amsterdam University of Applied Sciences in the Netherlands point out that a diet based mainly on plant foods can support these improvements, provided it supplies enough protein and is accompanied by regular training.
The main difference was in muscle mass in the arms and legs. The average increase was 0.66 kilograms in the omnivorous diet group, compared with 0.38 kilograms in the vegetarian group — an increase about 70% greater in the former. Both groups therefore gained muscle mass, but to different degrees. This difference was not accompanied by a corresponding statistically significant difference in improvements in strength and physical performance.
The reason for the difference remains unclear. The study leaves open whether it is related to lower protein intake in the vegetarian group or to the quality of protein from different foods. In the vegetarian group, higher protein consumption was associated with a greater increase in muscle mass, something not observed in the omnivorous group. The authors suggest that the latter may already have reached an intake level beyond which extra protein offered no additional benefit for muscle growth.
The results need careful interpretation, as the participants were mainly white, healthy and highly educated. It is unclear how far the findings apply to other populations. In addition, dietary research is influenced by many factors, including lifestyle, behaviour, genetics, social surroundings and environmental conditions. This particular trial records the results of a 12-week intervention.
The practical issue the researchers highlight is dietary adequacy in older age, when protein is particularly important for maintaining muscle. According to the authors, the suitability of a more plant-based diet also depends on individual circumstances. For people with a poor appetite or limited energy intake, particular attention is needed to the quantity and quality of protein. The findings support the possibility of building muscle strength with a vegetarian diet, while leaving open the question of the difference in muscle mass gains.
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