Dietary protein plays a critical role in the daily regulation of muscle mass by virtue of its ability to regularly stimulate muscle protein synthesis rates. Sarcopenia is mechanistically explained, at least in part, by the reduced responsiveness of older adult's muscle tissue to these anabolic properties of dietary protein. However, this 'anabolic resistance' can be overcome by paying attention to the synergy that exists between the anabolic effects of dietary protein and physical activity. Specifically, consuming dietary protein in close temporal proximity to physical activity and/or adequate amounts of dietary protein per meal is an effective strategy to optimise muscle protein metabolism in older adults. These mechanistic, physiological findings are supported by longitudinal studies showing that older individuals who consume modestly greater amounts of dietary protein than the current RDA, and/or maintain/adopt an active lifestyle, experience reduced rates of sarcopenia and typically live healthier lives.

With the importance of dietary protein to support active, healthy ageing evident, and a consequent scientific momentum moving towards a considerable (≥50%) rise in recommended protein intake for older individuals, the inevitable question arises: 'where should this dietary protein to support healthy ageing come from?' Current and future generations are required to view developments in human nutrition through the lens of mounting challenges associated with the sustainability of increased production of animal proteins, a concern also of primary importance to Quorn Foods. However, research into the nutritional physiology of alternative, sustainable, non-animal derived protein sources is in its infancy, particularly so in older adults. Therefore, there is considerable scientific interest, public health value and commercial opportunity in establishing a robust evidence base for the efficacy of non-animal, sustainably produced dietary protein sources to support active, healthy ageing.

Mycoprotein, a food source produced by continuous fermentation of the filamentous fungus Fusarium venenatum, imposes a significantly lower environmental burden during its production compared with animal sources. In collaboration with Quorn Foods, we recently reported that acute consumption of mycoprotein in young adults results in equivalent amino acid bioavailability to that of milk protein, and therefore shows promise as a protein source to support muscle anabolism and metabolic health in numerous populations. In the present proposal, we wish to translate and extend these findings into the older adult population. We will exploit a stable isotope tracer approach (oral administration of deuterium oxide \['heavy water'\]) to make in vivo measurements of cumulative, free living muscle protein synthesis rates in response to a highly sustainable, non-animal derived, mycoprotein based diet with or without physical activity, compared with a more traditional diet reliant on animal derived protein sources (matched for total protein). The study will increase our knowledge of how effective non-animal derived proteins are at supporting muscle tissue remodelling in the elderly.