Vegan and omnivorous diets equally effective for muscle building, University of Illinois study inds

A new clinical trial led by researchers at the University of Illinois Urbana-Champaign has found that vegan and omnivorous diets support muscle growth equally well when paired with resistance training, challenging long-held assumptions about the superiority of animal-based protein sources for muscle development.

The findings, published in Medicine and Science in Sports and Exercise, show that the rate of muscle protein synthesis – a key indicator of muscle growth – was unaffected by whether participants followed a plant-based or animal-based diet, how their protein was distributed throughout the day, or even whether their intake exceeded moderate daily protein recommendations.

The study was led by Nicholas Burd, a professor of health and kinesiology at the University of Illinois, and former graduate student Andrew Askow. “The longstanding belief or the current dogma was that animal-based protein sources were better, particularly for the muscle-building response,” said Burd. “But our results show that’s not the case – at least not when total protein intake is sufficient and the diet is balanced.”

The study included 40 physically active adults aged 20 to 40 who consumed either a vegan or omnivorous whole-food diet for nine days. Meals were designed to provide 1.1 to 1.2g of protein per kilogram of body weight per day, a level consistent with what the average American consumes. Protein intake was also split between those who consumed roughly equal amounts at each meal and those whose intake varied across the day.

To track muscle protein synthesis, participants drank deuterium-labeled water and underwent muscle biopsies before and after the intervention. All participants also engaged in strength training every three days.

Contrary to expectations based on prior research involving isolated protein supplements or single-meal tests, the study found no difference in muscle-building outcomes between diet groups or protein timing strategies.

“I was surprised,” Burd admitted. “We thought that a lower quality protein – in terms of digestibility and amino acid content – might benefit from being spaced out more during the day. But it turns out that it doesn’t matter. What matters most is simply consuming enough protein and exercising.”

Importantly, the vegan diets used in the study were carefully formulated to include complete protein profiles. This was achieved through whole-food pairings rather than reliance on supplements, making the findings more reflective of realistic dietary patterns.

The study was funded by the Beef Checkoff program, administered by the National Cattlemen’s Beef Board. Despite the funding source, the results did not support a performance advantage for meat-based diets.

“The best type of food for muscle building,” Burd said, “is the kind you put in your mouth after exercise. As long as it delivers sufficient high-quality protein, whether it’s plant-based or animal-based doesn’t really make a difference.”

The study, titled Impact of vegan diets on resistance exercise-mediated myofibrillar protein synthesis in healthy young males and females: A randomized controlled trial, is now available online.