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Randomized Controlled Trial
. 2014 Jan 22;13:9.
doi: 10.1186/1475-2891-13-9.

Postprandial Muscle Protein Synthesis Is Higher After a High Whey Protein, Leucine-Enriched Supplement Than After a Dairy-Like Product in Healthy Older People: A Randomized Controlled Trial

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Free PMC article
Randomized Controlled Trial

Postprandial Muscle Protein Synthesis Is Higher After a High Whey Protein, Leucine-Enriched Supplement Than After a Dairy-Like Product in Healthy Older People: A Randomized Controlled Trial

Yvette C Luiking et al. Nutr J. .
Free PMC article

Abstract

Background: Decreased ability of muscles to respond to anabolic stimuli is part of the underlying mechanism for muscle loss with aging. Previous studies suggest that substantial amounts of essential amino acids (EAA), whey protein and leucine are beneficial for stimulation of acute muscle protein synthesis in older adults. However, these studies supplied only proteins, and no bolus studies have been done with dairy products or supplements that contained also fat and carbohydrates besides proteins. The aim of this study was to evaluate whether a specifically designed nutritional supplement in older adults stimulates muscle protein synthesis acutely to a greater extent than a conventional dairy product. Moreover, the combined effect with resistance exercise was studied by using a unilateral resistance exercise protocol.

Methods: Utilizing a randomized, controlled, double blind study design, healthy older adults received a single bolus of a high whey protein, leucine-enriched supplement (EXP: 20 g whey protein, 3g total leucine, 150 kcal; n = 9) or an iso-caloric milk protein control (

Control: 6g milk protein; n = 10), immediately after unilateral resistance exercise. Postprandial mixed muscle protein fractional synthesis rate (FSR) was measured over 4h using a tracer infusion protocol with L-[ring-¹³C₆]-phenylalanine and regular blood and muscle sampling.

Results: FSR was significantly higher overall after EXP (0.0780 ± 0.0070%/h) vs CONTROL (0.0574 ± 0.0066%/h (EMM ± SE)) (p = 0.049). No interaction between treatment and exercise was observed (p = 0.519). Higher postprandial concentrations of EAA and leucine are possible mediating factors for the FSR response, while plasma insulin increase did not dictate the FSR response. Moreover, when the protein intake from the supplements was expressed per kg leg lean mass (LLM), a significant correlation was observed with resting postprandial FSR (r = 0.48, P = 0.038).

Conclusions: Ingestion of a high whey protein, leucine-enriched supplement resulted in a larger overall postprandial muscle protein synthesis rate in healthy older subjects compared with a conventional dairy product. This acute effect is promising for long-term effects on parameters of muscle mass, strength and function in sarcopenic older people, which requires further study.

Trial registration: This trial is registered in the Dutch Trial Register under number NTR1823.

Figures

Figure 1
Figure 1
Flow diagram. Flow diagram of participants.
Figure 2
Figure 2
Study design. Study design, including a screening visit, a 3-d standardization period, study visit and follow-up calls. At the study visit, participants underwent a stable isotope infusion protocol for 7¾ h, including an initial fasting period of 3¾ h until product intake (T = 0), regular blood sampling (arrows), 3 muscle biopsies (T = -45 and 240 min), and an unilateral resistance exercise intervention (T = -15 min).
Figure 3
Figure 3
Plasma amino acids. Plasma concentrations (means ± SEM) of leucine, essentials amino acids (EAA), sum of amino acids (AA), isoleucine, valine and phenylalanine before and after ingestion (at T = 0) of the study products EXP (n = 9) and Control (n = 10). Baseline values were not different between groups. iAUC values for leucine, EAA and AA were significantly higher after ingestion of EXP vs Control (P < 0.001). For leucine and EAA, peak and change-from-baseline concentrations were also significantly higher after ingestion of EXP vs Control (P < 0.001).
Figure 4
Figure 4
Plasma glucose and insulin. Plasma concentrations (means ± SEM) of glucose and insulin before and after ingestion (at T = 0) of the study products EXP (n = 9) and Control (n = 10). Baseline values were not different between groups. Peak glucose (P < 0.001) and glucose iAUC (P = 0.003) was significantly higher after ingestion of Control, but groups did not differ significantly in peak or iAUC insulin.
Figure 5
Figure 5
Plasma 13C6-Phe enrichment. Plasma enrichment of L-[ring-13C6]-phenylalanine (means ± SEM) expressed as molar percent excess (MPE), before and after ingestion (at T = 0) of the study products EXP (n = 9) and Control (n = 10).
Figure 6
Figure 6
Mixed muscle protein synthesis. Mixed muscle protein FSR (means ± SEM) with plasma L-[ring-13C6]-phenylalanine as precursor, over 4 h after ingestion of the study products EXP (n = 9) and Control (n = 10). Data are presented for resting leg and exercising leg separately.
Figure 7
Figure 7
Correlation between FSR and leg lean mass-corrected protein intake. Correlation between intake of protein from EXP (21 g) and Control (6 g) per kg leg lean mass (LLM) and postprandial FSR in the resting leg. Pearson’s correlation statistics is shown.

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