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.
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 (


METHODS
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.


BACKGROUND
This trial is registered in the Dutch Trial Register under number NTR1823.
Yvette C
YC
Luiking
Nicolaas E P
NE
Deutz
Robert G
RG
Memelink
Sjors
S
Verlaan
Center for Translational Research in Aging and Longevity, Donald W, Reynolds Institute on Aging, University of Arkansas for Medical Sciences, 4301 W, Markham St, Slot 806, Little Rock AR 72205, USA. rwolfe2@uams.edu.
Robert R
RR
Wolfe
D000368:Aged; D000601:Amino Acids, Essential / Q000008:administration & dosage*; D002247:Carbon Isotopes; D019587:Dietary Supplements; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D007930:Leucine / Q000008:administration & dosage*; D008297:Male; D008875:Middle Aged; D008894:Milk Proteins / Q000008:administration & dosage*; D009124:Muscle Proteins / Q000096:biosynthesis*; D019518:Postprandial Period; D000067816:Whey Proteins
D000601:Amino Acids, Essential; D002247:Carbon Isotopes; D008894:Milk Proteins; D009124:Muscle Proteins; D000067816:Whey Proteins; D007930:Leucine