In adults aged 74 ± 7 years, a protein bar with 16 grams of milk proteins and 1.5 grams of free leucine consumed two hours after a low-protein breakfast raises plasma leucine to about 590 µM and...
Mechanism
Synthesis from 1 study
The protein bar delivers a quick burst of leucine that tells muscle cells to start building protein, which pulls essential amino acids out of the blood and keeps their levels high for longer. This mimics the effect of eating a much larger protein meal without needing to consume more food.
Most probable mechanism
After eating a protein bar with added leucine, the leucine quickly enters the bloodstream and triggers a chain reaction in muscle cells that keeps essential amino acids circulating in the blood at high levels, matching what happens after eating a much larger protein meal.
Free leucine and leucine derived from milk proteins are rapidly absorbed from the small intestine into the bloodstream, causing plasma leucine concentration to rise to approximately 590 µM within two hours.
Elevated plasma leucine binds to Sestrin2 in skeletal muscle, releasing its inhibition of the mTORC1 complex and activating it.
Activated mTORC1 phosphorylates p70S6K and 4E-BP1, enhancing ribosomal activity and initiating the translation of messenger RNA into new muscle proteins.
The increased demand for amino acids to support protein synthesis triggers sustained release of essential amino acids from the bloodstream into muscle tissue, maintaining elevated plasma essential amino acid exposure over time.
Less supported by current evidence, but not ruled out
Leucine in the gut activates receptors that signal the brain to reduce hunger and increase fullness, which may help maintain stable nutrient intake patterns without requiring large meals.
Leucine and other amino acids bind to nutrient-sensing receptors on enteroendocrine cells in the small intestine.
Activated enteroendocrine cells release satiety hormones such as CCK, GLP-1, and PYY into the bloodstream.
These hormones stimulate vagal nerve fibers that transmit signals to the brainstem and hypothalamus, suppressing hunger-promoting neurons and activating fullness-promoting neurons.
Neural signaling reduces subjective hunger and increases perceived fullness, independent of total caloric intake.
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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