The Anabolic Properties of Fortified Plant-based Protein in Older People

Rationale: Consumption of sufficient dietary protein is fundamental to skeletal muscle mass maintenance and overall health. Conventional animal-based protein sources such as meat, poultry, fish, eggs, and dairy are considered high-quality sources of dietary protein. However, the production of sufficient amounts of these conventional animal-based proteins to meet future global food demands will be challenging. Consequently, there is a great interest in more sustainable alternatives for these high-quality protein sources. Plant-derived proteins can be produced on a more sustainable scale, but are generally considered lower quality protein sources compared to animal-based sources because of incomplete essential amino acid profiles, resulting in lower anabolic properties for skeletal muscle building. Blending different plant-derived proteins can be a solution, but will never match the profile of other high-quality animal-derived proteins, likely necessitating the fortification of such plant-based protein blends with essential amino acids such as leucine.Objective: To assess post-prandial muscle protein synthesis rates in older males in response to ingesting a blend of plant protein fortified with free leucine compared to (gold standard) whey protein and compared to the plant protein blend without additional leucine.Study design: randomized, parallel-group, double-blind, combined superiority non-inferiority, intervention trial.Study population: 45 healthy (BMI 18.5-30 kg/m2) older males (age: 60-75 y inclusive).Intervention: Subjects will consume a beverage containing 20g whey protein isolate, 20g of a plant protein blend or the same plant protein blend fortified with 2g leucine. Continuous intravenous stable isotope amino acid tracer infusions will be applied, with plasma and muscle samples collected at different time points throughout the experimental test day.Main study parameters/endpoints: The primary outcome will be postprandial (0-4h) muscle protein synthesis rates following beverage ingestion.

Inclusion Criteria:Male sexAged between 60 and 75 y inclusiveBMI between 18.5 and 30 kg/m2Exclusion Criteria:Vegetarian and vegan dietIntolerant to milk productsSoy allergyPea allergyParticipating in a structured (progressive) exercise program or >2.5h of vigorous physical activity per week.Smoking regularly (i.e. >5 cigarettes/week)Diagnosed GI tract disorders or diseasesDiagnosed musculoskeletal disordersDiagnosed metabolic disorders (e.g. diabetes)Diagnosed with phenylketonuria (PKU)Hypertension (blood pressure above 140/90 mmHg)Donated blood 3 months prior to test dayUse of any medications known to affect protein metabolism (i.e. corticosteroids, non-steroidal anti-inflammatories).Chronic use of gastric acid suppressing medicationChronic use of anti-coagulantsRecent (<1 year) participation in amino acid tracer studies (L-[ring-13C6]-phenylalanine and L-[3,5-2H2]-tyrosine)