In adults around 74 years old, eating a specific protein bar with 1.5 grams of leucine and 16 grams of milk protein causes plasma leucine levels to rise to about 590 micromoles per liter, which is...
Mechanism
Synthesis from 1 study
Eating the leucine-enriched bar causes blood leucine levels to spike higher than after a big protein meal. This high leucine level turns on a molecular switch in muscle cells that starts building new muscle proteins. This switch works better in older adults because their muscles normally don't...
Most probable mechanism
When a leucine-enriched protein bar is eaten, the free leucine and leucine from milk protein quickly enter the bloodstream, raising blood leucine levels to a high peak. This high concentration of leucine binds to a sensor in muscle cells, which turns on a key signaling pathway that tells the cell to start building new muscle proteins.
Free leucine and leucine derived from milk protein are rapidly absorbed from the gastrointestinal tract into systemic circulation, producing a sharp rise in plasma leucine concentration.
Elevated plasma leucine concentrations bind to Sestrin2 in skeletal muscle, relieving its inhibition of the mTORC1 complex and enabling its activation.
Activated mTORC1 phosphorylates downstream targets p70S6K and 4E-BP1, enhancing ribosomal biogenesis and cap-dependent translation initiation.
Increased translation initiation elevates the rate of muscle protein synthesis, overcoming age-related anabolic resistance.
Less supported by current evidence, but not ruled out
Leucine in the bloodstream triggers gut cells to release hormones that signal the brain to reduce hunger and increase fullness, independent of calorie intake.
Leucine and other amino acids activate nutrient-sensing receptors on enteroendocrine cells in the small intestine.
Activated enteroendocrine cells release satiety hormones including CCK, GLP-1, and PYY into the bloodstream.
Satiety hormones stimulate vagal afferent nerves that project to the nucleus tractus solitarius and hypothalamus.
Neural signals in the hypothalamus suppress orexigenic neurons and activate anorexigenic neurons, reducing subjective hunger and increasing fullness.
Evidence from Studies
Supporting (1)
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Consumption of High-Leucine-Containing Protein Bar Following Breakfast Impacts Aminoacidemia and Subjective Appetite in Older Persons
Contradicting (0)
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