Intake of low-dose leucine-rich essential amino acids stimulates muscle anabolism equivalently to bolus whey protein in older women at rest and after exercise

Am J Physiol Endocrinol Metab. 2015 Jun 15;308(12):E1056-65. doi: 10.1152/ajpendo.00481.2014. Epub 2015 Mar 31.


Dysregulated anabolic responses to nutrition/exercise may contribute to sarcopenia; however, these characteristics are poorly defined in female populations. We determined the effects of two feeding regimes in older women (66 ± 2.5 yr; n = 8/group): bolus whey protein (WP-20 g) or novel low-dose leucine-enriched essential amino acids (EAA) [LEAA; 3 g (40% leucine)]. Using [(13)C6]phenylalanine infusions, we quantified muscle (MPS) and albumin (APS) protein synthesis at baseline and in response to both feeding (FED) and feeding plus exercise (FED-EX; 6 × 8 knee extensions at 75% 1-repetition maximum). We also quantified plasma insulin/AA concentrations, whole leg (LBF)/muscle microvascular blood flow (MBF), and muscle anabolic signaling by phosphoimmunoblotting. Plasma insulinemia and EAA/aemia were markedly greater after WP than LEAA (P < 0.001). Neither LEAA nor WP modified LBF in response to FED or FED-EX, whereas MBF increased to a similar extent in both groups only after FED-EX (P < 0.05). In response to FED, both WP and LEAA equally stimulated MPS 0-2 h (P < 0.05), abating thereafter (0-4 h, P > 0.05). In contrast, after FED-EX, MPS increased at 0-2 h and remained elevated at 0-4 h (P < 0.05) with both WP and LEAA. No anabolic signals quantifiably increased after FED, but p70 S6K1 Thr(389) increased after FED-EX (2 h, P < 0.05). APS increased similarly after WP and LEAA. Older women remain subtly responsive to nutrition ± exercise. Intriguingly though, bolus WP offers no trophic advantage over LEAA.

Keywords: aging; amino acids; blood flow; exercise; protein synthesis; skeletal muscle.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Amino Acids, Essential / administration & dosage*
  • Amino Acids, Essential / blood
  • Diet
  • Dietary Proteins / administration & dosage*
  • Dietary Supplements
  • Exercise / physiology*
  • Female
  • Humans
  • Insulin / blood
  • Leucine / administration & dosage*
  • Leucine / blood
  • Middle Aged
  • Milk Proteins / administration & dosage*
  • Muscle Proteins / biosynthesis*
  • Muscle Proteins / drug effects
  • Muscle, Skeletal / drug effects*
  • Muscle, Skeletal / metabolism
  • Rest / physiology*
  • Whey Proteins


  • Amino Acids, Essential
  • Dietary Proteins
  • Insulin
  • Milk Proteins
  • Muscle Proteins
  • Whey Proteins
  • Leucine