Soy-dairy protein blend and whey protein ingestion after resistance exercise increases amino acid transport and transporter expression in human skeletal muscle

J Appl Physiol (1985). 2014 Jun 1;116(11):1353-64. doi: 10.1152/japplphysiol.01093.2013. Epub 2014 Apr 3.


Increasing amino acid availability (via infusion or ingestion) at rest or postexercise enhances amino acid transport into human skeletal muscle. It is unknown whether alterations in amino acid availability, from ingesting different dietary proteins, can enhance amino acid transport rates and amino acid transporter (AAT) mRNA expression. We hypothesized that the prolonged hyperaminoacidemia from ingesting a blend of proteins with different digestion rates postexercise would enhance amino acid transport into muscle and AAT expression compared with the ingestion of a rapidly digested protein. In a double-blind, randomized clinical trial, we studied 16 young adults at rest and after acute resistance exercise coupled with postexercise (1 h) ingestion of either a (soy-dairy) protein blend or whey protein. Phenylalanine net balance and transport rate into skeletal muscle were measured using stable isotopic methods in combination with femoral arteriovenous blood sampling and muscle biopsies obtained at rest and 3 and 5 h postexercise. Phenylalanine transport into muscle and mRNA expression of select AATs [system L amino acid transporter 1/solute-linked carrier (SLC) 7A5, CD98/SLC3A2, system A amino acid transporter 2/SLC38A2, proton-assisted amino acid transporter 1/SLC36A1, cationic amino acid transporter 1/SLC7A1] increased to a similar extent in both groups (P < 0.05). However, the ingestion of the protein blend resulted in a prolonged and positive net phenylalanine balance during postexercise recovery compared with whey protein (P < 0.05). Postexercise myofibrillar protein synthesis increased similarly between groups. We conclude that, while both protein sources enhanced postexercise AAT expression, transport into muscle, and myofibrillar protein synthesis, postexercise ingestion of a protein blend results in a slightly prolonged net amino acid balance across the leg compared with whey protein.

Keywords: leucine; mTORC1; muscle protein synthesis; protein anabolism; protein metabolism.

Publication types

  • Randomized Controlled Trial
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Administration, Oral
  • Adult
  • Amino Acid Transport Systems / biosynthesis*
  • Amino Acid Transport Systems / drug effects
  • Amino Acids / drug effects
  • Amino Acids / metabolism*
  • Dietary Proteins / administration & dosage*
  • Dietary Proteins / metabolism
  • Double-Blind Method
  • Eating / physiology
  • Female
  • Humans
  • Male
  • Milk Proteins / administration & dosage*
  • Muscle, Skeletal / drug effects
  • Muscle, Skeletal / physiology*
  • Resistance Training / methods*
  • Soybean Proteins / administration & dosage*
  • Soybean Proteins / pharmacokinetics
  • Up-Regulation / drug effects
  • Up-Regulation / physiology
  • Whey Proteins
  • Young Adult


  • Amino Acid Transport Systems
  • Amino Acids
  • Dietary Proteins
  • Milk Proteins
  • Soybean Proteins
  • Whey Proteins