Aging is accompanied by a loss of skeletal muscle mass and muscle strength. Besides
physical activity, the consumption of sufficient dietary protein is fundamental to
skeletal muscle mass maintenance and overall health. As older individuals express
anabolic resistance to protein intake, it is thought that older people can improve the
anabolic response by ingesting higher protein doses. However, ingesting large protein
doses is not always feasible. Alternatively, protein quality represents an important
factor affecting the anabolic response to food intake.
Conventional animal-based protein sources such as meat and dairy are generally considered
high-quality sources of dietary protein because they meet all of the indispensable amino
acid requirements for humans and are highly digestible. However, the production of
sufficient amounts of these conventional animal-based proteins to meet future global food
demands represents a massive challenge. Presently, there is a great interest in
plant-based proteins as a more sustainable alternative for animal-based proteins. Current
data shows that plant-based proteins are generally of a lesser quality when compared to
animal-based protein, like whey protein, as evidenced by a lower indispensable amino acid
content and deficiencies in one or more specific amino acids (i.e. lysine, leucine and/or
methionine). This also translates to a compromised bioavailability and lesser anabolic
properties. Studies show that ingestion of a single bolus of a plant protein increases
muscle protein synthesis rates to a lesser extent when compared to animal-based proteins.
Combining different types of plant-derived proteins to overcome the amino acid
deficiencies has been proposed as a strategy to increase the anabolic properties of
plant-derived proteins. However, it is not possible to match the amino acid composition
to that of the gold standard, whey protein. Another strategy to improve the anabolic
properties of plant-derived proteins is fortification with free essential amino acids.
Previously, ingestion of 40g of protein as a lysine fortified meat substitute was shown
to increase muscle protein synthesis rates to a similar level as the ingestion of
chicken. However, it is unclear whether this similarity was caused by the lysine
enrichment or by the ingestion of a really high dose of protein that could have maximized
muscle protein synthesis rates. Therefore, the principle of fortification is still to be
investigated with the ingestion of a much lower (submaximal, but more realistic) dose of
20g protein.
Therefore, the aim of the current study is to assess postprandial muscle protein
synthesis rates in older males in response to ingestion of a blend of plant protein (20g)
fortified with free leucine, as compared to the blend of plant protein without additional
leucine, and compared to whey protein as the gold standard.
Two primary hypotheses will be tested:
it is hypothesized that postprandial muscle protein synthesis rates will be higher
following ingestion of the fortified plant protein blend when compared to the normal
plant protein blend
it is hypothesized that postprandial muscle protein synthesis rates will be at least
as high following ingestion of the fortified plant protein blend when compared to
whey protein.
