Numerous studies have shown that dietary protein intake plays a crucial role in promoting muscle protein synthesis, a key factor in skeletal muscle growth and maintenance. Recent research findings indicate significant differences in the effectiveness of animal and plant protein sources in stimulating muscle growth and maintaining muscle. This difference is primarily attributed to differences in protein quantity and quality, as well as differences in the essential amino acid (EAA) content of these food sources.

Comparative Study of Protein Sources

A new study recently published in the Journal of Nutrition is one of the first randomized controlled trials to compare the anabolic properties of whole protein foods as part of a mixed meal. The study found that in older adults, a whole-food mixed meal containing lean beef resulted in higher rates of postprandial muscle protein synthesis than a whole-food vegetarian meal, despite having the same caloric and total protein content. In fact, researchers observed that muscle protein synthesis was 47% higher after eating an omnivorous meal containing lean beef compared to a whole-food vegetarian meal that provided the same amount of plant protein.

Lucvan Loon, Ph.D., professor of exercise and nutritional physiology in the Department of Human Biology at Maastricht University Medical Center and principal investigator of this study, said: "Previous studies have evaluated the effects of consuming isolated proteins, while this study aimed to reflect a more real-life context by understanding the effects of whole protein foods as part of a typical meal. Given the importance of protecting lean body mass to maintain strength as we age, and the growing interest in vegetarian and vegan lifestyles, this study is important to understand whether protein food sources are equally effective in supporting muscle maintenance and growth."

Based on previous studies comparing intake of different protein sources, the researchers calculated that 16 participants would be needed to complete the study and detect potential differences in muscle protein synthesis rates after consuming the two meals. Therefore, researchers conducted a clinical trial on 16 healthy older adults (65-85 years old) in Maastricht, the Netherlands. On one test day, participants ate a whole-food multigrain meal that included 3.5 ounces of lean ground beef as the primary protein source, potatoes, green beans, applesauce (made from 100 percent apples), and herb butter.

Another test day included eating a whole-food vegetarian meal of equal caloric and protein content based on unprocessed, commonly consumed plant-based protein foods such as quinoa, soybeans, chickpeas, and fava beans. Importantly, both meals contained an average of 36 grams of protein, which is in line with evidence-based recommendations for stimulating muscle protein synthesis in older adults (i.e. 0.45 grams of protein per kilogram of body weight).

"We were interested in studying the effect of mealtime on muscle protein synthesis in older adults because of the importance of age-related loss of muscle mass and strength, known as sarcopenia, which is a growing public health problem worldwide," vanLoon added.

Research findings and implications

All participants abstained from physical and strenuous exercise and did not consume alcohol during the two days preceding the two experimental days. The researchers compared postprandial plasma amino acid profiles and muscle protein synthesis rates using blood and muscle biopsy samples taken frequently within six hours of eating. In addition to observing a 47% increase in muscle protein synthesis within 6 hours of the meal, the researchers also noted that despite the absence of any selective amino acid deficiencies with the vegetarian meal, EAA concentrations in the lean beef postmeal plasma were 127% higher.

"Importantly, participants' plasma levels of leucine, an essential amino acid particularly important for muscle protein synthesis, were 139% higher after eating an omnivore meal containing beef," said Philippe Pinckaers, MSc, lead author of the publication. "This study illustrates the potential influence of food matrix and the importance of differences in amino acid bioavailability and biological function between beef-containing and vegetarian diets."

Compiled source: ScitechDaily