Background Protein intake is important for skeletal muscle mass maintenance with aging and the ingestion of specifically-timed protein supplements could increase overall protein intake and thereby contribute to skeletal muscle mass maintenance. Recently, more attention has been given to the ingestion of plant-based protein blends as a more sustainable high-quality alternative to milk protein, as a means to increase muscle protein build-up and, as such, support muscle maintenance, especially when consuming suboptimal amounts of protein in the regular diet.

Objective To assess the benefit of daily protein supplementation with either a plant-based protein blend or a milk protein on top of a standard diet to stimulate integrated muscle protein synthesis rates in healthy older individuals with and without exercise.

Hypotheses It is hypothesized that both the plant protein blend and the milk protein supplement will result in greater muscle protein build-up when compared with a standard diet control condition.

It is also hypothesized that exercise will result in greater muscle protein build-up when compared to the resting leg in all conditions, with similar effects of the protein supplements vs the control diet as in the non-exercised leg.

This study will show the potential benefit of protein supplementation with alternative protein sources to support skeletal muscle maintenance in older individuals.

Inclusion Criteria:

• Male or female sex
• Aged between 60 and 80 y inclusive
• BMI between 18.5 and 30 kg/m2

Exclusion Criteria:

• Following a self-reported vegetarian and vegan diet the 6 months prior to the study.
• Intolerant to milk products
• Corn allergy
• Pea allergy
• Participating currently or in the 3 months prior to the study in a structured (progressive) exercise program.
• Smoking regularly (i.e. >5 cigarettes/week)
• History of cardiovascular, respiratory, gastrointestinal, urogenital, neurological, psychiatric, dermatologic, musculoskeletal, metabolic, endocrine, haematological, immunologic disorders, allergy, major surgery and/or laboratory assessments which might limit participation in or completion of the study protocol, interfere with the execution of the experiment, or potential influence the study outcomes (to be decided by the principal investigator and responsible physician)
• Diagnosed with phenylketonuria (PKU)
• Uncontrolled hypertension (blood pressure above 160/100 mmHg)
• Donated blood 3 months prior to test day
• Use of any medications that interferes with study participation and/or outcomes (i.e. corticosteroids, non-steroidal anti-inflammatories, gastric acid suppressing medication) as assessed by the responsible medical doctor.
• Use of DOAC, vitamin-K-antagonist, or multiple anticoagulants
• Pregnancy

Protein supplements are packed the same and look and taste similar.