Effects of vegan diets and lifestyle on adult body composition: a narrative review

Abstract

The health benefits of vegan diets are well documented, though achieving nutritional adequacy requires careful planning, as is the case with any well-designed diet. Vegan diets effectively address obesity, with emerging evidence suggesting that body composition analysis offers a more accurate assessment of body weight management than traditional body mass index (BMI) calculations. This narrative review evaluates the impact of vegan diets on adult body composition based on 16 human interventional studies (published between 01/2014–10/2024), sourced from the PubMed/Medline database across various countries, including the USA, Canada, Brazil, Chile, and several European countries. Findings indicate that vegan diets can lead to greater reductions in body weight and more favourable changes in body composition compared to control diets, including high carbohydrate lacto-ovo, traditional and vegan-type Mediterranean, animal-based ketogenic, portion-controlled, therapeutic omnivorous and Western-type diets. However, some studies report significant muscle mass loss. Strategies to mitigate this include regular physical activity, particularly resistance training, ensuring sufficient protein intake and applying modest energy restrictions without compromising nutrient adequacy. Individual factors such as baseline BMI and health status also influence outcomes. This review further addresses critical real-world questions and dilemmas to deepen understanding of the relationship between vegan diet, body composition, and overall health, thus contextualizing the theme. Future research should explore whether a well-designed vegan diet, combined with customized lifestyle interventions, can further improve muscle mass preservation and overall body composition outcomes compared to other dietary lifestyles.