Gastrointestinal mechanisms in the ‘anorexia of ageing’ – effects of dietary protein

Abstract

Involuntary weight loss in older people reflecting of a decline in appetite and energy, mainly protein, intake, is associated with the development of undernutrition and increased morbidity and mortality, and is termed the ‘anorexia of ageing’. A common strategy for management of undernutrition in older people is the use of nutritional supplements which are usually high-energy drinks, rich in whey protein. In younger adults, whey protein, when compared to other proteins, is perceived as a ‘fast-acting’ protein, with a rapid satiating effect. Given that protein is the most satiating macronutrient in younger people, and its substitution for other macronutrients is often advocated to promote weight loss, it is possible that the satiating effects of increased protein ingestion could counteract some, or all, of the positive effects of increased protein ingestion in older people on muscle mass and function. Despite the increasing use of protein-rich drinks by older people, information about their effects on energy intake, appetite and underlying gastrointestinal mechanisms in this age group is limited. The primary aim of this thesis was to determine the effects of dietary protein on energy intake, appetite and underlying gastrointestinal mechanisms, including antropyloroduodenal motility, gastric emptying and plasma gut hormone concentrations in healthy older when compared to younger adults. The studies produced clear-cut results - ingestion of whey protein was less suppressive of feeding behaviour in older than younger adults, so that there was an increase in total energy intake in the elderly. Younger adults showed suppression of perception of appetite after protein ingestion when compared to control, while older adults increased their appetite. Energy intake at a buffet meal was not affected by the timing of protein ingestion before the meal. Young women, in contrast to men, did not show suppression of ad libitum energy intake after oral protein preloads. Older compared to younger adults, and women compared to men, had slower gastric emptying of whey protein drinks. Ageing appears especially to affect the initial phase of gastric emptying of protein. In older adults, plasma CCK and GIP concentrations after protein ingestion were higher compared to young adults. In conclusion, the regulation of appetite and energy intake is impaired in the elderly. In particular, the acute suppression of energy intake by whey protein is less in healthy older, than younger, adults, resulting in increased overall energy intake in the older adults.