Effects of leucine-enriched essential amino acid and whey protein bolus dosing upon skeletal muscle protein synthesis at rest and after exercise in older women.
Level 2 - randomized trial
Controlled interventional trial in humans measuring acute physiological outcomes
PubMed 29031484 · doi:10.1016/j.clnu.2017.09.008
What was done
Twenty-four older women (mean age 65 ± 1 years) were allocated to three groups (n = 8 per group) receiving either 1.5 g of leucine-enriched essential amino acids (LEAA_1.5, containing 0.6 g leucine), 6 g of leucine-enriched essential amino acids (LEAA_6), or 40 g of whey protein (WP). Muscle protein synthesis (MPS) was measured via primed constant intravenous infusion of 13C6-phenylalanine at baseline, after feeding alone (FED), and after feeding combined with unilateral resistance exercise (FED-EX; 6 sets of 8 leg extensions at 75% 1-RM). Plasma insulin and amino acid concentrations, leg femoral blood flow, muscle microvascular blood flow, and anabolic signaling were also assessed.
What was found
The abstract does not provide absolute numeric values for synthesis rates, blood flow, or hormone concentrations. Reported directional and significance findings include: - Plasma insulin and essential amino acid levels were greater and more prolonged with WP than LEAA, though peak concentrations were similar between LEAA_6 and WP. - Neither LEAA nor WP altered leg femoral or muscle microvascular blood flow. - Under resting feeding conditions (FED), MPS increased similarly across all three groups over 0–2 hours (P < 0.05), but remained significantly elevated above baseline over 0–4 hours only in the LEAA_6 and WP groups. - Under exercise-plus-feeding conditions (FED-EX), MPS increased similarly across all three groups from 0 to 4 hours (P < 0.05). - Phosphorylated p70S6K1 increased only in the WP group at 2 hours in FED (P < 0.05) and at 2 and 4 hours in FED-EX (P < 0.05).
Why it matters
These findings suggest that low doses of leucine-enriched essential amino acids can stimulate post-exercise muscle protein synthesis in older women to a degree comparable to a large whey protein bolus, indicating that leucine composition rather than total protein mass drives acute post-exercise anabolism.
Limits
The sample size was small (n = 8 per group) and randomization is not explicitly stated in the abstract. Only older females were studied, limiting generalizability to males or other age cohorts. The study evaluated only acute 4-hour postprandial responses without measuring long-term changes in muscle mass, strength, or clinical sarcopenia outcomes.
Cited by
- supports Administering free leucine or branched-chain amino acids increases muscle protein synthesis strongly in the first 2 hours, but the response wears off much more rapidly than intact protein.