A Lower Protein Leucine‐matched Beverage Induces Similar Increases in Acute and Integrated Muscle Protein Synthesis in Healthy Older Women

Sarcopenic muscle and strength loss negatively impact health. Sarcopenic muscle loss may have a multi‐faceted etiology, but the predominant mechanism is thought to be a phenomenon termed anabolic resistance. Anabolic resistance describes a refractoriness of muscle protein synthesis (MPS) to feeding‐induced hyperaminoacidemia in older versus younger persons. Older adults have a lower food intake and older women in particular may not be consuming adequate protein to stimulate MPS. Objective To determine whether the addition of leucine to a smaller dose (10g) of mixed milk protein can induce similar increases in acute and integrated myofibrillar MPS as an isoenergic, 25 g dose of whey protein isolate (WPI). Methods Healthy, older women (n = 11/group) were recruited and randomized to one of 2 groups: 1) WPI: consumption of 25 g WPI (3 g leucine), 2/d or 2) P10: consumption of 10 g milk protein concentrate with 3 g leucine (Glanbia Nutritionals, PepForm ® ), 2/d. One leg was randomized to the exercised condition and maximal strength was determined (1‐RM). For determination of acute myofibrillar MPS, participants underwent primed constant infusion of 13 C 6 ‐phenylalanine and MPS was determined in the fasted, fed (rested) and fed + exercised (4 sets, 50–60% 1 RM, one leg) state. For determination of integrated myofibrillar MPS, participants consumed D 2 O (100 mL) and MPS was determined prior to (basal) and during supplementation in the rested and exercised leg. Participants were provided with all food to be consumed for 2 days prior to the acute trial (basal period) and throughout the 6 d supplementation period. The diet consisted of 1.0 g/kg/d protein. During the supplementation period the study beverages were incorporated into subjects' diets such that the participant continued to consume 1.0 g/kg/d protein. Results Acute myofibrillar MPS did not differ between groups in the fasted state. MPS increased in both the rested and exercised leg in response to P10 (fasted: 0.030 ± 0.003%/h, fed: 0.046 ± 0.003%/h, fed+exercise: 0.056 ± 0.002%/h; p < 0.001) and WPI (fasted: 0.034 ± 0.001%/h, fed: 0.044 ± 0.002%/h, fed+exercise: 0.051 ± 0.002%/h; p < 0.001), with no differences between groups. Acute MPS was greater in response to feeding in the exercised as compared with rested leg (p < 0.001). There was no difference in basal rates of integrated myofibrillar MPS between groups (WPI: 1.52 ± 0.01%/d vs P10: 1.53 ± 0.03%/d). MPS increased with WPI during the supplementation period in both the rested (1.56 ± 0.02%/d, p = 0.02) and exercised (1.66 ± 0.02%/d, p < 0.001) legs. MPS increased with P10 in the exercised leg (1.67 ± 0.02%/d, p < 0.001) during the supplementation period with a trend for an increase in the rested leg (1.56 ± 0.02%/d, p = 0.1). Conclusion A lower (10 vs. 25 g) protein beverage with equal leucine content induced similar increases in acute and integrated myofibrillar MPS in healthy, older women. Lower protein nutritional supplements with added leucine may represent an advantageous approach in older adults to maintain skeletal muscle anabolic sensitivity and alleviate muscle loss. Support or Funding Information PepsiCo Global R&D

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