Greater Leucine Content Enhances the Acute and Integrated Muscle Protein Synthetic Responses Versus an Isonitrogenous, Isoenergetic Protein Beverage in Healthy Older Women
Authors: Devries Michaela C , McGlory Christopher , Tuerke Diane , Bolster Douglas R , Kamil Alison , Rahn Maike , Harkness Laura , Phillips Stuart M 
Published: November 2023

A decreased anabolic response to protein feeding is one of the mechanisms that underpins sarcopenic muscle loss with aging, with older adults requiring a higher protein dose than younger adults to increase muscle protein synthesis (MPS). Despite this knowledge, a number of commercially available protein beverages targeted to increase protein intake and support lean body mass in older adults contain ≤20 g of protein, and their ability to stimulate MPS in this population is unknown. Leucine has, however, been shown to enhance the MPS response to lower doses of protein and thus may represent an effective ‘anti‐sarcopenic’ ingredient.ObjectiveTo compare the acute and integrated myofibrillar MPS response to a typical commercial protein beverage to that of an isonitrogenous, isoenergetic protein beverage with added leucine in older women.MethodsHealthy, older women (n = 11/group) were recruited and randomized to one of 2 groups: 1) CON: 15 g mixed protein beverage (soy isolate, milk concentrate and caseinate), 2/d; 2) P15: 15 g milk protein concentrate with 4 g leucine (Glanbia Nutritionals, PepForm®), 2/d. Unilateral maximal strength was determined (1‐RM) and one leg was randomized to an exercise condition. For determination of acute MPS, participants underwent a primed constant infusion of 13C6‐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 MPS, participants consumed 100 mL of D2O and MPS was determined prior to (basal) and during 6 d supplementation in the rested and exercised leg. Participants were provided with all food to be consumed throughout the basal and supplementation period, which consisted of 1.0 g/kg/d protein. During the supplementation period the study beverages were incorporated into the diet such that the participant continued to consume 1.0 g/kg/d protein.ResultsAcute MPS was the same in the fasted state in both groups (CON: 0.034 ± 0.001%/h, P15: 0.034 ± 0.001%/h). Feeding increased MPS in the rested (CON: 0.038 ± 0.001%/h, P15: 0.053 ± 0.002%/h) and exercised (CON: 0.043 ± 0.001%/h, P15: 0.064 ± 0.002%/h) leg in both groups, but the increase was greater with P15 (p < 0.001). Integrated MPS was the same in the basal state in both groups (CON: 1.52 ± 0.03%/d, P15: 1.48 ± 0.03%/d). MPS increased with P15 during the supplementation period in both legs (rested: 1.62 ± 0.03%/d, exercised: 1.73 ± 0.03%/d; p < 0.001), but in the exercised leg only with CON (rested: 1.54 ± 0.02%/d, exercised: 1.62 ± 0.02%/d; p < 0.001) and was greater with P15 than CON in both legs (p < 0.001).ConclusionsA protein beverage fortified with 4 g of leucine induced greater increases in acute and integrated MPS than an isonitrogenous protein beverage containing protein equivalent to typical commercially available beverages. As opposed to consumption of P15, which increased MPS, chronic consumption of the CON protein beverage did not increase MPS and thus would not likely attenuate the loss of muscle mass in older adults.Support or Funding InformationPepsiCo Global R&D