Postexercise Dietary Leucine Retention for Whole-Body Anabolism Is Greater With Whey Protein Isolate and Fish-Derived Protein Hydrolysate Than Nonessential Amino Acids in Trained Young Men

Marine-derived proteins, such as blue whiting-derived protein hydrolysates (BWPH), represent high-quality sources of dietary protein, but their ability to support postexercise anabolism is not established. The impact of BWPH on whole-body anabolism was compared with an isonitrogenous whey protein isolate (WPI) and nonessential amino acid (NEAA) control in 10 trained young males (31 ± 4 years) who, on three separate visits, performed a session of whole-body resistance exercise and then consumed, in randomized crossover fashion, BWPH, WPI, or NEAA (0.33 g/kg; 19, 33, and 0 mg/kg leucine, respectively) with L-[1-13C]leucine. Breath, blood, and urine samples were collected for 6-hr postprandial to assess dietary leucine oxidation, amino acid (AA) concentrations, and 3-methylhistidine: creatinine ratio. Peak and area under the curve concentrations for leucine, branched-chain amino acids, and essential amino acids were greater in WPI compared with BWPH (all p < .05) but with no differences in time to peak concentration. Total oxidation reflected leucine intake (WPI > BWPH > NEAA; p < .01), whereas relative oxidation was greater (p < .01) in WPI (28.6 ± 3.6%) compared with NEAA (21.3 ± 4.2%), but not BWPH (28.6 ± 8.8%). Leucine retention, a proxy for whole-body protein synthesis, was greater in WPI (185.6 ± 9.5 μmol/kg) compared with BWPH (109.3 ± 14.1 μmol/kg) and NEAA (5.74 ± 0.30 μmol/kg; both p < .01), with BWPH being greater than NEAA (p < .01). Urinary 3-methylhistidine: creatinine ratio did not differ between conditions. Both WPI and BWPH produced essential aminoacidemia and supported whole-body anabolism after resistance exercise, but a higher intake of BWPH to better approximate the leucine and EAA content of WPI may be needed to produce an equivalent anabolic response.