Challenging the belief that animal protein is the superior type for building muscle, scientists have shown that there is actually no difference in eating meat and dairy or plant sources following a workout.
Researchers from the University of Illinois Urbana-Champaign recruited 40 physically active participants – 28 males, 12 females – aged between 20 and 40 years, who took part in a seven-day "habituation diet" to reset their bodies ahead of the protein trial. Then, they were randomly assigned either a nine-day vegan or omnivorous eating plan designed by the scientists.
The omnivore diet featured at least 70% animal protein and included beef, pork, chicken, dairy and eggs. The vegan diet paid special attention to the amino acid content, to ensure the plant proteins were complete and comparable to the animal sources. Overall, participants ate around 1.1-1.2 grams of protein per kilogram of body weight each day.
Then, the groups were divided further: Some participants ate around the same amount of protein across three meals each day, while the others had varying percentages of protein in five meals for the same time period, with the largest amount late in the day.
During this time, everyone performed weight-based muscle-strengthening workouts every three days in the laboratory. Accelerometers also monitored physical activity outside of the lab environment.
In addition to this, the participants drank "heavy" or deuterated (D20) water each day, which is a common way of tracing the metabolic synthesis of protein and amino acids – essentially to gauge how the body was using the protein eaten. This way, the team was able to see how this protein was being used by muscle tissue in the body.
When leg muscle biopsies were taken at the end of the trial, and compared to samples before the experiment commenced, lead researcher Nicholas Burd was surprised by the results. Because there were no differences in how the muscle had synthesized the two protein sources in the diets, nor was there an impact of incorporating protein evenly in meals throughout the day.
“It was thought that it was better to get a steady-state delivery of nutrients throughout the day,” Burd 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.”
If you'd ever tried to work out what protein and when, in efforts to maximize muscle growth and strength, you'll know that literature on the topic can get overwhelming. This study shows that no, it doesn't matter what the source of the protein is, nor whether the amount is eaten once or split across meals throughout the day.
“The longstanding belief or the current dogma was that animal-based protein sources were better, particularly for the muscle-building response,” said Burd.
Much of the previous science comes from studies that compared single events of protein intake followed by muscle tissue analysis. Here, studies have found that animal protein does synthesize more rapidly.
“And so, our general hypothesis based on these previous studies was that the animal-based eating pattern would be more effective at supporting the muscle-building response," he added.
This latest study was also more reflective of real-world protein intake than previous research. An earlier long-term trial, over 10 weeks, had also shown no significant difference in muscle building in participants on either animal or plant diets, but had required people to eat much more protein than needed (1.6-1.8 grams of protein per kilogram of their bodyweight). The participants eating vegan had also received most of their protein as supplements, which is a poor comparison of diets focused on protein in whole foods.
"Our results demonstrated that the anabolic action of animal vs. vegan dietary patterns are similar," the researchers wrote. "Moreover, there is no regulatory influence of distribution between the two dietary patterns on the stimulation of myofibrillar protein synthesis rates in young adults."
While gym-goers may still swear by their post-workout whey shake, Burd said the best is simply "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," he added.
Interestingly, this trial was supported by the National Cattlemen’s Beef Board.
The study was published in the journal Medicine and Science in Sports and Exercise.
