Abstract
BACKGROUND & AIM: Dietary protein digestion and absorption plays an important role in modulating postprandial muscle protein synthesis. The impact of co-ingesting other macronutrients with dietary protein on protein digestion and absorption and the subsequent muscle protein synthetic response remains largely unexplored. This study investigated the impact of co-ingesting milk fat with micellar casein on dietary protein-derived amino acid appearance in the circulation and the subsequent postprandial muscle protein synthetic response in healthy older men. METHODS: Twenty-four healthy, older males (age: 65 +/- 1 y, BMI: 25.7 +/- 0.5 kg/m2) received a primed continuous infusion of L-[ring-2H5]-phenylalanine and L-[1-13C]-leucine and ingested 20 g intrinsically L-[1-13C]-phenylalanine and L-[1-13C]-leucine-labeled casein with (PRO + FAT; n = 12) or without (PRO; n = 12) 26.7 g milk fat. Plasma samples and muscle biopsies were collected in both the postabsorptive and postprandial state. RESULTS: Release of dietary protein-derived phenylalanine into the circulation increased following protein ingestion (P < 0.001) and tended to be higher in PRO compared with PRO + FAT (Time x Treatment P = 0.076). No differences were observed in dietary protein-derived plasma phenylalanine availability (52 +/- 2 vs 52 +/- 3% in PRO vs PRO + FAT, respectively; P = 0.868). Myofibrillar protein synthesis rates did not differ between treatments, calculated using either the L-[ring-2H5]-phenylalanine (0.036 +/- 0.003 vs 0.036 +/- 0.004 %/h after PRO vs PRO + FAT, respectively; P = 0.933) or L-[1-13C]-leucine (0.051 +/- 0.004 vs 0.046 +/- 0.004 %/h, respectively; P = 0.480) tracer. In accordance, no differences were observed in myofibrillar protein-bound L-[1-13C]-phenylalanine enrichments between treatments (0.018 +/- 0.002 vs 0.014 +/- 0.001 MPE, respectively; P = 0.173). CONCLUSION: Co-ingesting milk fat with micellar casein does not impair protein-derived phenylalanine appearance in the circulation and does not modulate postprandial myofibrillar protein synthesis rates. CLINICAL TRIAL REGISTRATION NUMBER: NCT01680146 (http://www.clinicaltrials.gov/).
Original language | English |
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Pages (from-to) | 429-437 |
Number of pages | 9 |
Journal | Clinical Nutrition |
Volume | 36 |
Issue number | 2 |
DOIs | |
Publication status | Published - Apr 2017 |
Keywords
- Muscle protein synthesis
- Fat
- Casein
- Leucine
- Sarcopenia
- INTRINSICALLY LABELED MILK
- ESSENTIAL AMINO-ACIDS
- HUMAN-NUTRITION RESEARCH
- NURSING-HOME RESIDENTS
- INTRAGASTRIC DISTRIBUTION
- ELDERLY-MEN
- MUSCLE
- HUMANS
- ACCRETION
- GLUCOSE