Study Finds No Difference in Muscle Growth Between Vegan and Omnivorous Diets After Weight Training

A recent study conducted by researchers from the University of Illinois at Urbana-Champaign has revealed that the source of dietary protein—whether plant-based or animal-based—does not significantly influence muscle protein synthesis following weight training. The investigation aimed to answer three key questions: Does protein source affect muscle gain? Does even distribution of protein intake throughout the day matter? And does a moderate daily protein intake influence these outcomes?

The study’s findings challenge the long-held belief that animal-based proteins are superior for muscle building. Previous studies suggested that meals containing animal proteins elicited a stronger response in muscle protein synthesis compared to vegan meals—based on muscle biopsy data after a single feeding. However, these studies did not assess the impact of sustained dietary patterns over time.

In this trial, 40 healthy, active young adults aged 20-40 were assigned to vegan or omnivorous diets, with all meals provided by the research team. The omnivorous diet consisted mainly of animal products like beef, pork, chicken, dairy, and eggs, while the vegan diet was carefully balanced to supply complete proteins through plant-based sources. Participants also varied in their protein distribution: some consumed equal amounts at three meals, others spread their intake over five meals with more protein later in the day.

Throughout the study, every three days, participants engaged in muscle-strengthening exercises and wore accelerometers to monitor their daily activity levels. To measure muscle protein synthesis precisely, the researchers used labeled heavy water as a tracer, alongside muscle biopsies taken before and after the intervention.

Unexpectedly, the results showed no significant difference in muscle protein synthesis between vegan and omnivorous diets, regardless of how protein was distributed across meals. Despite prior assumptions favoring steady nutrient delivery, this study indicates that as long as sufficient high-quality protein is consumed—around 1.1 to 1.2 grams per kilogram of body weight daily—the source and timing of intake are less critical.

Lead researcher Nicholas Burd emphasized that the findings suggest individuals can achieve muscle growth with either diet type, focusing primarily on total protein intake post-exercise. "It doesn't matter whether your protein comes from plants or animals, as long as you're getting enough," he stated.

The study underscores the importance of realistic dietary patterns, as many participants on vegan diets received their protein from whole foods rather than supplements, reflecting typical eating habits. It also highlights that moderate protein intake, aligned with average diets, is sufficient for supporting muscle development alongside resistance training.

This research challenges previous notions and encourages flexibility in dietary choices for athletes and fitness enthusiasts aiming to build muscle. It emphasizes that the most important factor is ensuring adequate high-quality protein intake after workouts, regardless of dietary preferences.