This type of meat supercharges muscle growth after workouts

The research was published in the American Journal of Clinical Nutrition.

“What we’re finding is that not all high-quality animal protein foods are created equal,” said Nicholas Burd, a professor of health and kinesiology at the University of Illinois Urbana-Champaign, who led the research with graduate student Žan Zupančič.

Burd’s previous work revealed similar patterns. One earlier experiment showed that eating whole eggs after weight training led to greater muscle-protein synthesis than eating the same amount of protein from egg whites alone. Another study found that eating salmon produced a stronger muscle-building response than consuming a processed blend with the same nutrients in identical proportions.

Together, these findings suggest that whole foods stimulate muscle growth more effectively after exercise than processed versions do. Burd noted that in some cases, the natural fat content of whole foods might actually enhance muscle-building activity.

In this latest study, the research team used advanced techniques to measure and track muscle-protein synthesis in 16 young, physically active adults. To prepare the test meals, they collaborated with the University of Illinois Meat Science Laboratory to create pork patties with precisely defined fat levels.

“That took us a year because it was so hard to get those fat ratios correct,” Burd said. All of the meat came from a single pig, and the patties were sent to an external lab for detailed nutrient analysis. Once the fat-to-lean ratios and other nutritional values were verified, the burgers were frozen until used during the experiment’s feeding phase.

Before participants began the workout and meal trials, they received an infusion of isotope-labeled amino acids. This technique allowed the scientists to monitor how quickly those amino acids were integrated into muscle tissue. Blood samples were also collected throughout the process to measure circulating amino acid levels.

Muscle biopsies were taken both before and after the two-hour infusion to establish a baseline for muscle-protein synthesis.

“And then we took them to the gym,” Burd said. “And they were wheeling that infusion pump and everything else with them.”

At the gym, participants performed leg presses and leg extensions, then returned to the lab to eat one of three test meals: a high-fat pork burger, a lean pork burger, or a carbohydrate drink. Five hours later, the researchers took another muscle biopsy to measure how the meal and exercise together affected protein synthesis.

After several days of recovery, 14 of the 16 volunteers repeated the process but switched meal types to ensure that individual differences did not skew the results.

As expected, amino acid levels in the blood rose sharply after eating pork compared with the carbohydrate drink. However, those who consumed the lean pork burger showed the largest increases in amino acids — both total and essential.

“When you see an increased concentration of amino acids in the blood after you eat, you get a pretty good idea that that is coming from the food that you just ate,” Burd said.

Those who consumed the lean pork burger after a bout of weight training also had a greater rate of muscle-protein synthesis than those who ate the high-fat pork burger. This was a surprise to Burd, as “the previous studies using fattier foods, such as whole eggs or salmon, generally showed enhanced post-exercise muscle-protein synthesis compared with lower fat food such as egg whites or nutritional supplements,” he said.

Although weight training boosted muscle-protein synthesis in the groups eating pork, the protein in the high-fat burger seemed to have no added benefit in the hours after participants consumed it, while the protein in the lean pork gave muscle-protein synthesis a boost.

“For some reason, the high-fat pork truly blunted the response,” Burd said. “In fact, the people who ate the high-fat pork only had slightly better muscle-building potential than those who drank a carbohydrate sports beverage after exercise.”

Interpreting the results of this study for people who want to optimize muscle gains from weight-training is tricky, Burd said. It could be that processing the ground pork patties, which involved grinding the meat and adding the fattier meat to the lean, affected the kinetics of digestion.

“There was a little larger rise in the amino acids available from eating lean pork, so it could have been a bigger trigger for muscle-protein synthesis,” Burd said. “But that seems to be specific to the ground pork. If you’re eating other foods, like eggs or salmon, the whole foods appear to be better despite not eliciting a large rise in blood amino acids.”

Burd stresses that exercise is the strongest stimulus for muscle-protein synthesis.

“Most of the muscle response is to weight-training, and we use nutrition to try to squeeze out the remaining potential,” he said. “When it comes to eating after weight-training, what we’re finding is that some foods, particularly whole, unprocessed foods seem to be a better stimulus.”

Burd also is a professor of nutritional sciences and is affiliated with the Carl R. Woese Institute for Genomic Biology at the U. of I.

The National Pork Board’s Pork Checkoff program supported this research. The funder had no involvement in study design, data collection or analysis.