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Abstract
SummaryBackground & aimsNutritional composition is key for skeletal muscle maintenance into older age. Yet the acute effects of collagen protein blended with other protein sources, in relation to skeletal muscle anabolism, are ill-defined. We investigated human muscle protein synthesis (MPS) responses to a 20 g blend of collagen protein hydrolysate + milk protein (CP+MP, 125 ml) oral nutritional supplement (ONS) vs. 20 g non-blended milk protein source (MP, 200 ml) ONS, in older adults.MethodsHealthy older men (N = 8, 71±1 y, BMI: 27±1 kg·m−2) underwent a randomized trial of 20 g protein, from either a CP+MP blend (Fresubin®3.2 kcal DRINK), or a kcal-matched (higher in essential amino acids (EAA) ONS of MP alone. Vastus lateralis (VL) MPS and plasma AA were determined using stable isotope-tracer mass spectrometry; anabolic signaling was quantified via immuno-blotting in VL biopsies taken at baseline and 2/4 h after ONS feeding. Plasma insulin was measured via enzyme-linked immunosorbent assay (ELISA). Measures were taken at rest, after the feed (FED) and after the feed + exercise (FED-EX) conditions (unilateral leg exercise, 6 × 8, 75% 1-RM).ResultsMP resulted in a greater increase in plasma leucine (MP mean: 152 ± 6 μM, CP+MP mean: 113 ± 4 μM (Feed P < 0.001) and EAA (MP mean: 917 ± 25 μM, CP+MP mean: 786 ± 15 μM (Feed P < 0.01) than CP+MP. CP + MP increased plasma glycine (peak 385 ± 57 μM (P < 0.05)), proline (peak 323 ± 29 μM (P < 0.01)) and non-essential amino acids (NEAA) (peak 1621 ± 107 μM (P < 0.01)) with MP showing no increase. Plasma insulin increased in both trials (CP+MP: 58 ± 10 mU/mL (P < 0.01), MP: 42 ± 6 mU/mL (P < 0.01), with peak insulin greater with CP+MP vs. MP (P < 0.01). MPS demonstrated equivalent increases in response to CP+MP and MP under both FED (MP: 0.039 ± 0.005%/h to 0.081 ± 0.014%/h (P < 0.05), CP+MP: 0.042 ± 0.004%/h to 0.085 ± 0.007%/h (P < 0.05)) and FED-EX (MP: 0.039 ± 0.005%/h to 0.093 ± 0.013%/h (P < 0.01), CP+MP: 0.042 ± 0.004%/h to 0.105 ± 0.015%/h, (P < 0.01)) conditions. FED muscle p-mTOR fold-change from baseline increased to a greater extent with CP+MP vs. MP (P < 0.05), whilst FED-EX muscle p-eEF2 fold-change from baseline decreased to a greater extent with CP+MP vs. MP (P < 0.05); otherwise anabolic signaling responses were indistinguishable.ConclusionFresubin®3.2 kcal DRINK, which contains a 20 g mixed blend of CP+MP, resulted in equivalent MPS responses to MP alone. Fresubin® 3.2 Kcal DRINK may provide a suitable alternative to MP for use in older adults and a convenient way to supplement calories and protein to improve patient adherence and mitigate muscle mass loss.
Highlights
Maintenance of skeletal muscle mass across the life-course is dependent upon intake of adequate dietary protein; this is because amino acids (AA) within dietary proteins acutely stimulate muscle protein synthesis (MPS) and thereby replenish muscle protein stores lost to muscle protein breakdown (MPB) in times of fasting [1]
The milk-protein blend (MP) drink showed significantly greater increases in plasma essential AA (EAA) (MP mean: 917 ± 25 mM, CPþMP mean: 786 ± 15 mM (Feed P < 0.01), branched chain amino acids (BCAA) (MP mean: 475 ± 25 mM, CPþMP mean: 372 ± 15 mM (Feed P < 0.001) and leucine (MP mean: 152 ± 6 mM, CPþMP mean: 113 ± 4 mM (Feed P < 0.001) concentrations which remained elevated above baseline for 150e200 min
Plasma nonessential amino acids (NEAA) only increased in response to CPþMP (Fig. 2B), with glycine (Fig. 2D) and proline (Fig. 2F) increasing rapidly in responses to CPþMP, peaking at ~75e100 min and remaining elevated for ~250min
Summary
Maintenance of skeletal muscle mass across the life-course is dependent upon intake of adequate dietary protein; this is because amino acids (AA) within dietary proteins acutely stimulate muscle protein synthesis (MPS) and thereby replenish muscle protein stores lost to muscle protein breakdown (MPB) in times of fasting [1]. A major feature of aged muscle would seem to be impaired handling of dietary proteins; reflecting this, many research groups have shown that older individuals' anabolic response to protein intake is blunted with advancing age [6e8]. The composition of AA in distinct protein sources can differ markedly, as can the ‘biological value’ based upon digestibility, bioavailability and/or tissue utilization [12,13]. Another major area of research in terms of ageing skeletal muscle and dietary protein intake, relates to distinct protein sources and their biological effects [14], in the context of acute muscle protein turnover and muscle mass outcomes - with or without exercise. Measures were taken at rest, after the feed (FED) and after the feed þ exercise (FED-EX) conditions (unilateral leg exercise, 6 Â 8, 75% 1-RM)
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