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A recent investigation delves into how dietary protein sources and distribution impact muscle protein synthesis during a nine-day diet and weight training program. The study posed three pertinent questions: Firstly, does the type of protein—plant-based or animal-based—affect muscle growth? Secondly, is evenly distributing protein intake throughout the day beneficial? Thirdly, does a moderate daily protein intake play a role in these outcomes? The researchers concluded that none of these factors significantly influenced the muscle-building process.
The results of this study have been published in the journal Medicine and Science in Sports and Exercise.
According to Nicholas Burd, a professor at the University of Illinois Urbana-Champaign and the study’s lead author, traditional views have favored animal-based proteins for their supposed superiority in muscle growth. This perspective, he noted, was grounded in earlier research where muscle biopsies following single meals indicated that animal proteins sparked greater muscle protein synthesis compared to their plant-based counterparts. “Our hypothesis was shaped by these past findings, suggesting that consuming animal-based proteins would be more effective for muscle development,” Burd elaborated.
However, Burd pointed out the limitations of focusing solely on single meal responses, which do not accurately capture the effects of a balanced vegan diet over an extended period.
Prior research had examined muscle responses in vegans and omnivores consuming a controlled diet while engaging in weight training for ten weeks. This earlier study reported no notable differences in muscle protein synthesis over time. Yet, the participants consumed a high protein intake ranging from 1.6 to 1.8 grams per kilogram of body weight daily, exceeding the amount required for maximizing muscle growth. Furthermore, the protein for those on the vegan diet predominantly came from supplements, which does not accurately reflect typical vegan eating habits.
The current research aimed to investigate whether a consistent and varied diet of whole foods—either plant-based or animal-based—would affect muscle protein synthesis over time, as opposed to merely relying on single meals or restricted protein sources. Additionally, the study explored the notion that evenly spreading a moderate protein intake, specifically about 1.1 to 1.2 grams of protein per kilogram of body weight daily, could enhance muscle growth.
Burd’s previous findings indicated that protein intake above 1.1 g/kg per day does not improve muscle protein synthesis rates during weight training. He emphasized the importance of testing real-life dietary patterns, as this amount aligns more closely with typical American diets.
For the new study, the team enlisted 40 healthy, physically active adults aged between 20 and 40. Participants initially followed a seven-day “habituation diet” to standardize their nutritional status before entering the main trial. They were then randomly assigned to either a vegan diet or an omnivorous one, with the research team preparing all meals—most of which were consumed at home. Approximately 70% of the protein in the omnivorous diet was sourced from animal products such as beef, pork, chicken, dairy, and eggs. The vegan meals were designed to provide complete proteins through a balanced amino acid profile.
Within each dietary group, participants were further categorized based on how they distributed their protein intake: either evenly across three meals or variably across five meals throughout the day, with a greater share consumed later.
Throughout the study, participants engaged in muscle-strengthening exercises in the lab every three days and wore activity trackers to monitor their movements outside of lab sessions.
Participants also consumed deuterated water—water enriched with a stable isotope of hydrogen—which permitted researchers to trace its incorporation into muscle tissue by marking the amino acids as “heavy.” Muscle biopsies were taken from a leg muscle both before and after the trial.
Burd expressed surprise at the findings that revealed no significant differences in muscle protein synthesis rates between the vegan and omnivorous groups. He was also taken aback by the lack of impact related to the distribution of protein intake on muscle growth, contradicting prior studies which suggested that steady nutrient delivery was critical. “It was previously believed that a steady supply of nutrients throughout the day was advantageous,” he noted. “I also thought that lower quality proteins might affect this. Surprisingly, our results show that this is not the case.”
Now, Burd advises that when it comes to muscle building, the focus should be on the type of food consumed post-exercise. “As long as you’re obtaining adequate high-quality protein from your diet, the specific source becomes less significant,” he remarked.
This research received support from the Beef Checkoff program, which is managed by the National Cattlemen’s Beef Board.
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