Abstract
SummaryBackground & aimsImpaired anabolic responses to nutrition and exercise contribute to loss of skeletal muscle mass with ageing (sarcopenia). Here, we tested responses of muscle protein synthesis (MPS), in the under represented group of older women, to leucine-enriched essential amino acids (EAA) in comparison to a large bolus of whey protein (WP).MethodsTwenty-four older women (65 ± 1 y) received (N = 8/group) 1.5 g leucine-enriched EAA supplements (LEAA_1.5), 6 g LEAA (LEAA_6) in comparison to 40 g WP. A primed constant I.V infusion of 13C6-phenylalanine was used to determine MPS at baseline and in response to feeding (FED) and feeding-plus-exercise (FED-EX; 6 × 8 unilateral leg extensions; 75%1-RM). We quantified plasma insulin/AA concentrations, leg femoral blood flow (LBF)/muscle microvascular blood flow (MBF), and anabolic signalling via immunoblotting.ResultsPlasma insulineamia and EAAemia were greater and more prolonged with WP than LEAA, although LEAA_6 peaked at similar levels to WP. Neither LEAA or WP modified LBF or MBF. FED increased MPS similarly in the LEAA_1.5, LEAA_6 and WP (P < 0.05) groups over 0–2 h, with MPS significantly higher than basal in the LEAA_6 and WP groups only over 0–4 h. However, FED-EX increased MPS similarly across all the groups from 0 to 4 h (P < 0.05). Only p-p70S6K1 increased with WP at 2 h in FED (P < 0.05), and at 2/4 h in FED-EX (P < 0.05).ConclusionsIn conclusion, LEAA_1.5, despite only providing 0.6 g of leucine, robustly (perhaps maximally) stimulated MPS, with negligible trophic advantage of greater doses of LEAA or even to 40 g WP. Highlighting that composition of EAA, in particular the presence of leucine rather than amount is most crucial for anabolism.
Highlights
IntroductionIt is well established that following the intake of protein/amino acids there is a transient increase in muscle protein synthesis (MPS) (peaking at ~2 h; [7,8]), which assists to replenish protein lost during periods of fasting and maintaining stable muscle mass in young adults
As expected whey protein (WP) showed greater plasma AA availability than both the leucine enriched essential amino acids (LEAA) groups with essential amino acids (EAA), BCAA and leucine concentrations remaining significantly elevated above baseline up to 220 min, whereas concentrations in the LEAA_6 group returned to baseline within 80 min
While plasma insulin returned to near basal concentration 40 min after both 1.5 g and 6 g LEAA intake, insulin concentrations in response to 40 g of WP were significantly elevated up to 60 min, with significantly higher insulin concentrations at 20, 40 and 60 min compared to the LEAA
Summary
It is well established that following the intake of protein/amino acids there is a transient increase in MPS (peaking at ~2 h; [7,8]), which assists to replenish protein lost during periods of fasting and maintaining stable muscle mass in young adults. This “anabolic window” for increasing MPS with nutrition is extended when nutrition is combined with exercise [9e11]. We tested responses of muscle protein synthesis (MPS), in the under represented group of older women, to leucine-enriched essential amino acids (EAA) in comparison to a large bolus of whey protein (WP). Highlighting that composition of EAA, in particular the presence of leucine rather than amount is most crucial for anabolism
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