The progressive ageing of our population imposes an increasing demand on our healthcare systems. Ageing is associated with a decline in skeletal-muscle mass and function, accompanied by reduced physical performance, loss of functional capacity and an increased risk of developing chronic metabolic diseases and obesity. To date, the mechanisms behind the progressive loss of muscle mass, and the potential dietary interventions to counteract this process, are incompletely understood. The aim of this project was to elucidate the mechanisms regulating muscle-mass gain and loss in response to food ingestion and energy-intake restriction. In addition, this project defined dietary strategies and novel nutritional concepts to preserve muscle mass and support healthy ageing.
The regulatory mechanisms behind muscle-mass gains and losses were investigated in a large clinical trial. State-of-the-art research techniques (arterio-venous balances, stable-isotopes infusion, intrinsically-labelled protein, hyperinsulinemic euglycemic clamp, blood-flow measurements) were applied in young and elderly individuals to gain insight into the role of insulin in postprandial muscle-protein metabolism.
Although it is well known that dietary protein is essential for building and preserving muscle mass, the impact of the other macronutrients on muscle-mass gains and losses remained to be established. A series of mechanistic studies was completed to assess the impact of the macronutrient composition of a meal on the post-prandial muscle-protein synthetic response. These studies provided an answer to the question of whether the addition of carbohydrate (1st study) and fat (2nd study), to a protein-rich meal, modulates post-prandial muscle-protein metabolism. The third study investigated the effect of a habitual high-protein diet compared with normal-protein diet on digestion and absorption kinetics, and the subsequent muscle-protein synthetic response to dietary-protein ingestion. A longer-term randomised controlled trial was performed in parallel, to determine whether a high-protein diet can effectively preserve muscle mass during energy-intake restriction.
Another work package investigated the impact of the macronutrient composition of a nutritional supplement on postprandial skeletal-muscle-protein synthesis in the elderly. In addition, a follow-up study evaluated the course of pre-existing muscle-fibre atrophy, in elderly females with fall-related hip fracture, during hospital admission and the impact of a nutritional supplement (Pro-Hip).
It has been speculated that factors other than ageing might contribute to the loss of muscle mass in older individuals. Therefore, a work package, with acute human intervention trials, was initiated to investigate the role of gender, physical inactivity and obesity in relation to muscle-mass preservation.