Investigating the Digestibility, Bioavailability and Utilisation of Varied Combined Protein Sources in Older Males Using a Dual Stable Isotope Tracer Technique

By 2020, over 20% of the UK population will be over 65 years of age, dramatically increasing pressure on health and social care. Muscle mass is a strong predictor of healthy ageing and longevity. However, ageing is associated with a progressive loss of muscle, so-called sarcopenia, and this begins in mid-life. Because of the associated loss of muscle strength and stamina, sarcopenia is a major cause of disability, frailty and loss of independence, and is associated with an increased risk of falling and fractures in older people. Strategies to prevent or reduce sarcopenia are receiving increasing attention due to the growing numbers of elderly members of society, but the links between cause and effect are not easy to discern. The investigator's previous work has shown that there are deficits in mechanisms of muscle protein synthesis (MPS) in older people, but why these deficits exist and how they might be countered is still unknown. One of the major problems with ageing is that stimuli which would normally, in younger people, help maintain muscle by turning on MPS (to build muscle) are less effective in older people. The investigator's research has shown that in muscle, the major stimulant of adult human MPS is the availability of the so-called essential amino acids (AA) (which we have to obtain from our diet). After normal feeding, AA and insulin availability both rise, causing net gain of muscle protein. Although these processes do occur in the muscle of older people, they do not occur to the same extent as in the young. Similar results have also been obtained by others, and this is called "anabolic resistance". To exemplify, recent data the investigators have produced showed that: i) increasing the amount of protein provided has a smaller anabolic effect on MPS in older people, and ii) the anabolic response to acute resistance exercise is also less in older people. Understanding the basic mechanisms underlying age-associated muscle loss would help to define possi