A study published in Medicine and Science in Sports and Exercise found that both plant-based diets and animal-based diets equally promote muscle growth when daily protein intake is adequate, according to NPR. The study analyzed how muscle protein synthesis responds to a nine-day diet combined with resistance training involving 40 healthy and physically active participants, as reported by SciTechDaily.
The researchers recruited 40 healthy adults aged between 20 and 40 years. Before the official experiment, all participants followed a seven-day habituation diet to standardize their nutritional status. After this period, participants were randomly assigned to either a vegan or omnivorous diet for nine days.
Each group was further subdivided: some received a uniform distribution of protein in the three main meals, while others followed a variable distribution pattern across five meals, with a higher protein load towards the end of the day. The omnivorous diet consisted of approximately 70% protein from animal sources such as beef, pork, chicken, eggs, and dairy. The vegan diet was carefully balanced to ensure complete intake of essential amino acids, with one group receiving supplements to aid in this.
All participants performed muscle-strengthening activities every three days in the laboratory as part of a training program and were closely monitored during these sessions. They also wore accelerometers to record their physical activity outside the study environment. The research team provided all meals, some of which were eaten in the lab while most were consumed at home.
Researchers performed muscle tissue biopsies from a leg muscle at the beginning and end of the evaluation to measure muscle growth, which allowed them to calculate protein synthesis. Participants drank water with stable hydrogen isotopes labeled with deuterium to measure muscle mass accurately. The deuterium atoms exchanged with hydrogen atoms within amino acids to make them heavy and served as tracers that allowed the team to trace their incorporation into muscle tissue.
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The trial investigated protein intake timing, revealing no difference in muscle protein synthesis whether proteins were ingested before or after workouts, or spaced out throughout the day. The results support that, under conditions of adequate intake, the source of protein and its daily distribution do not significantly affect muscle growth.
"The long-held belief was that animal-based protein sources were better, particularly for the muscle-building response. The research showed, however, that they were not: that the animal-based dietary pattern was not more effective in supporting the muscle-building response," said Nicholas Burd, a professor of health and kinesiology at the University of Illinois at Urbana-Champaign and co-leader of the study. He added, "For a long time, it has been held, almost as a dogma, that animal proteins are superior for muscle development," as reported by SciTechDaily.
Burd was surprised to find no differences in rates of muscle protein synthesis between those eating vegan or omnivorous diets. He noted, "One thought that an even nutrient intake distributed over the day would be better," but found that protein distribution throughout the day had no influence on muscle building. He also thought distribution might make a difference when consuming lower-quality proteins in terms of digestibility and amino acid content but stated, "And surprisingly, we have shown that it doesn't matter."
These findings challenge the long-held belief that animal proteins are superior to plant proteins for muscle development. The study posed three key questions regarding muscle protein synthesis and protein intake. According to the authors of the study, the answer to all three questions was negative.
"On a gram-for-gram basis, animal protein is certainly of a higher quality than plant-based protein. But if you're consuming enough of [plant-based protein] and in the context of a whole meal, those differences really don't come out in the wash," said James McKendry, a researcher at the University of British Columbia.
"I think it's an important study with respect to our attitudes towards where we get our protein from," said Benjamin Wall, a researcher at the University of Exeter. Wall mentioned that in recent years, more well-controlled studies have shown that plant protein can be comparable to animal protein for building muscle. "We now have several studies which suggest there's far less difference," he stated.
"It's what you eat after training. As long as you get enough high-quality protein from food, it doesn't matter," Burd concluded.