Being omnivorous or vegan makes no difference to muscle building after weight training

Also, the team from University of Illinois at Urbana-Champaign in the US refuted two more claims about if total daily protein intake is evenly distributed throughout the day and does a moderate but sufficient daily protein intake influence any of these variables. Their findings are reported in the journal Medicine and Science in Sports and Exercise.

"The longstanding belief or the current dogma was that animal-based protein sources were better, particularly for the muscle-building response," said Nicholas Burd, a professor of health and kinesiology at the University of Illinois Urbana-Champaign.

Previous studies that took muscle biopsies after a single feeding found that an animal-based meal provided more of a stimulus for muscle protein synthesis than a vegan meal.

"But measurements taken after a single meal might not reflect the effects of consuming a balanced vegan diet over time," Burd argued.

For the new study, the team recruited 40 healthy, physically active 20-40-year-old adults.

The participants underwent a seven-day "habituation diet" to standardize their nutritional status prior to the clinical trial. Then they were randomly assigned to either a vegan or omnivorous diet.

Roughly 70 per cent of the protein for the omnivorous meals was obtained from animal sources: beef, pork, chicken, dairy, eggs. The vegan diet balanced the amino acid content of the meals, ensuring that participants consumed complete proteins.

All participants engaged in a series of muscle-strengthening activities in the lab every three days.

Burd was initially surprised to see that there were no differences in rates of muscle protein synthesis between those eating vegan or omnivorous diets.

He also was surprised to see that protein distribution across the day had no effect on the rate of muscle building given results from past studies of acute responses to dietary interventions and weight training.

"It was thought that it was better to get a steady-state delivery of nutrients throughout the day," he said. "I also thought that if you're getting a lower quality protein -- in terms of its digestibility and amino acid content -- that perhaps distribution would make a difference. And surprisingly, we showed it doesn't matter."

Now, Burd says, if anyone asks him what's the best type of food they should eat for muscle building, he'll tell them: "It's the kind you put in your mouth after exercise. As long as you're getting sufficient high-quality protein from your food, then it really doesn't make a difference."