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Clin Nutr. 2017 Apr;36(2):429-437. doi: 10.1016/j.clnu.2015.12.011. Epub 2015 Dec 24.

Co-ingesting milk fat with micellar casein does not affect postprandial protein handling in healthy older men.

Author information

1
NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University Medical Centre+, Maastricht, The Netherlands; Top Institute Food & Nutrition (TIFN), Wageningen, The Netherlands.
2
NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University Medical Centre+, Maastricht, The Netherlands.
3
Department of Anesthesia and Intensive Care, Karolinska University Hospital, Huddinge, Sweden.
4
NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University Medical Centre+, Maastricht, The Netherlands; Top Institute Food & Nutrition (TIFN), Wageningen, The Netherlands. Electronic address: L.vanLoon@maastrichtuniversity.nl.

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 × 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/).

KEYWORDS:

Casein; Fat; Leucine; Muscle protein synthesis; Sarcopenia

PMID:
26774526
DOI:
10.1016/j.clnu.2015.12.011
[Indexed for MEDLINE]
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