Anabolic Response to Beef vs Plant Protein in (Pre)Frail Older Adults Using a Novel Stable Isotope Pulse Method

Beef protein is known for its anabolic properties due to its high EAA levels and digestibility (\~ 94% compared to 78% in beans and 86% in whole wheat). However, whether beef has the most optimal composition of individual EAA and non-essential amino acids (NEAA) for older adults with (pre)frailty remains unclear as well as the role of the individual branched-chain amino acids (BCAA) leucine, isoleucine and valine. Research is of scientific and clinical importance to understand whether (pre)frail older adults respond better to certain protein sources (i.e., beef protein) due to a more optimal profile/pattern of individual EAA and NEAA amino acids. The study will take place at the research facility of the Center for Translational Research on Aging and Longevity (CTRAL), Texas A\&M University located in the Human Clinical Research Building ) affiliated with Texas A\&M University. The study involves 1 screening visit of approx. 3 hours, and 4 study days. Some study procedures (e.g., body composition, skeletal muscle function, questionnaires) may be skipped if completed within the past 3 months at CTRAL. All data will be recorded in Case Report Form and stored in the Texas A\&M REDCap System. Subjects will be asked to arrive in the fasted state on all study days. Fasting prior to screening is not required. On the screening day, body weight, height, and body composition by Dual-energy X-ray absorptiometry (DXA) will be measured. In addition, The Six-Minute Walk Test (6MWT) and skeletal muscle function tests will be assessed at the end of each screening visit. Each study visit will begin with vital signs. Before administration of the feeding or the tracer solution, baseline blood will be collected for measurement of the natural enrichment of metabolites. After the baseline sample is collected, feeding will begin and will be followed by tracers of several compounds that may be administered by IV pulse. Participants will receive bites and sips of nutrition every 20 minutes for 5 hours. Participants will consume, using a randomized cross-over design, using a bite feeding method of the following proteins: (1) beef, (2) tofu (soy as the most popular plant-based protein) or (3) water (placebo to correct the anabolic data obtained after intake of the proteins for baseline (postabsorptive) values).