Isotope Labeling

The purpose of this study is to understand how cells of the immune system use the common sugar glucose during critical illness. Investigators will intravenously infuse a non-radioactive carbon-13 glucose tracer into adult intensive care unit (ICU) participants over a few hours and collect immune cells from the blood to track uptake and usage of this glucose within these immune cells.

In the present semi-crossover randomized design, 15 recreationally active young adults (19-40 y) will receive stable isotope tracer infusions and perform a single bout of resistance exercise. Immediately after exercise, participants will ingest either 1 medium russet potato with skins and 2 ounce-equivalent lean ground beef combination (274 kcals, 19.3 g protein, 5 g fat, 37 g carbohydrates, and 4 g fiber), 2 slices of white bread and beef combination (262 kcals, 19.8 g protein, 6.8 g fat, 28 g carbohydrates, and 1.8 g fiber) or 2 ounce-equivalent beef (93% lean meat/7% fat; 110 kcals, 14.8 g protein, and 5 g fat). Repeated blood and muscle biopsies will be collected to determine whole body leucine kinetics, amino acid concentrations, anabolic signaling and myofibrillar protein synthesis rates during the trials.

The purpose of this study is to understand how cells of the immune system use the common sugar glucose to fuel energy production and as a building block within the cell. Investigators will intravenously infuse a non-radioactive glucose tracer into participants over a few hours and collect immune cells from the blood to track uptake and usage of this glucose within these immune cells.