Meat consumption supports higher essential amino acid bioavailability than plant-based proteins, study finds

16 Aug 2023 --- A recent study conducted by Purdue University researchers revealed that eating the same amount of animal protein as plant-based protein produced greater essential amino acids (EAA) bioavailability in adults. The outcomes were published in MDPI.

The study authors purport the findings may have public health nutrition guidance implications and serve as an important resource for future Dietary Guidelines for Americans (DGAs) to reevaluate the appropriateness of equating different protein sources in the protein foods group on an ounce-equivalent (oz-eq) basis across the lifespan.

“These results are also pertinent to the DGA’s recommendation to consume more plant-based foods,” says Dr. Wayne Campbell, primary investigator on the study and professor in the department of nutrition Science at Purdue University.

“While there are health benefits to consuming more plant-based foods, guidance on the importance of nutrient-dense animal-based protein foods, which are high-quality protein sources, is important information to incorporate when providing dietary recommendations,” he explains.

Evaluating DGAs recommendations
Two-ounce equivalents of the proteins were compared in the study. The 2020–2025 DGA recommends consuming “protein foods” as part of a healthy dietary pattern.

The DGAs emphasize eating various protein foods based on ounce-equivalent (oz-eq) portions with similar nutritional content. One oz-eq equals one ounce of meat, one whole egg, 0.25 cups of beans or 0.5 ounces of nuts.The Purdue University researchers recommend that their findings be taken into consideration in the drafting of the DGAs.

“Consuming meals with two oz-eq of animal-based protein foods resulted in more EAAs in the bloodstream compared to meals with two oz-eq of plant-based protein foods in both young and older adults, separately and combined,” explains Dr. Gavin Connolly, clinical trials project manager and research associate in the department of nutrition science at Purdue University. 

Protein foods differ in their energy and nutrient content, including protein quantity and quality. The protein quality of a particular food, essentially its EAA content, is a major factor in how the body uses amino acids for muscle and whole-body protein building.  

According to the researchers, protein bioavailability differs in populations. Younger adults may be more vulnerable to a lack of variety in their protein choices, while older adults might not eat sufficient high-quality sources of nutrient-dense protein. 

“Portion sizes of the protein foods in the study likely do not truly reflect the amounts consumed on a meal-to-meal or weekly basis by young or older adults. There were no direct measures of changes in muscle protein synthesis or whole-body protein balance in response to the meals containing the different protein foods,” Connolly explains.

Muscle building with EAA
Lean pork showed greater EAA bioavailability than eggs in young or older adults, separately or combined. There were no differences in EAA bioavailability between black beans and almonds and no differences between young and older adults.

“This means animal-based proteins (from unprocessed lean pork loin and scrambled eggs) more effectively provide EAAs, which is linked with the ability for our bodies to build body protein or muscle. This is an important consideration for muscle and whole-body health and physical function across the life course,” Connolly suggests.

The research defines protein quality as the ability of a dietary protein source to provide adequate amounts and proportions of EAA, which can only be obtained via dietary consumption, that are digestible and become bioavailable for use in the body for metabolic processes, such as stimulating protein synthesis and maintaining or growing body tissues.The bioavailability of a specific protein determines the levels of EAA processed by the body. 

One oz-eq of pork loin contains 7 g of total protein and one oz-eq of almonds contains 3 g of total protein. 

Method to the research
The scientists carried out two cross-over randomized controlled trials on 30 healthy young adults and 25 older adults. Each participant completed four 300-minute trials, each separated by a minimum of three days.

The order in which the participants completed their assignments was revealed to the scientists when all the recruits were done with the testing and the results were analyzed. The participants ate a standard meal with two oz-eq of animal-based protein foods (e.g., unprocessed lean pork loin, scrambled whole eggs) or plant-based protein foods (black beans, raw sliced almonds).

Blood samples were taken at baseline and 30, 60, 120, 180, 240, and 300 minutes after eating to determine EAA bioavailability. Blood sugar and insulin levels were also measured.

Additional research is needed to better understand how animal versus plant-based protein foods may influence muscle and whole-body health across the lifespan to promote healthy aging. The research was funded by the Pork Checkoff and the American Egg Board – Egg Nutrition Center.

By Inga de Jong