Effects of whey protein, on energy intake, appetite, antral area, gastric emptying, amino acids, gut hormones and glucose in healthy, undernourished and obese, young and older, individuals

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Ageing is associated with a physiological reduction of appetite and energy intake, which has been called the “anorexia of ageing”. Dietary supplementation with liquid protein preparations is now used frequently to increase energy and protein intake in older adults in both institutionalized and community-dwelling populations. Although the latter would appear a logical approach, evidence for success of increased energy intake in older individuals is limited. Urgent investigation is warranted to determine the optimal load of protein that can be incorporated into their diet to assist in sparing muscle mass without reducing their appetite. Moreover, weight loss protein-rich diets are often recommended for obese older adults in the same manner as for younger adults. In young adults, obese individuals exhibit a less precise compensatory response to ingested energy than lean individuals. Although only a limited number of studies have examined the effects of state of nutrition in elderly on the regulation of appetite, there is persuasive evidence of substantial differences between undernourished and healthy older people, which may potentially represent an outcome of and/or contribute to the undernourished state. A common strategy to increase energy intake and body weight in undernourished elderly is the use of nutritional supplements, and this is now almost standard practice. Usually such supplements are provided as mixed macronutrient high-energy drinks. Because of the increasing awareness of the major muscle loss that preferentially accompanies weight loss in older people, and its particular adverse effects, there has been a recent, marked, increase in the preferential administration of protein in these supplements and the use of protein-enriched supplements in an attempt to preserve, or even increase, muscle mass, in both institutionalized and community-dwelling populations. Such recommendations and use are, however, largely empirical. Our understanding of the feeding responses, and mechanisms underlying them, of undernourished and obese older people to protein is very limited and will be increased greatly by the proposed study. To aim of the study is to characterise in undernourished and obese, young and older individuals, the effect of different oral protein loads on energy intake, appetite, antral area, gastric emptying, plasma concentrations of amino acids, hormones (i.e. CCK, PYY, ghrelin, GLP-1, GIP, glucagon and insulin) and glucose, and to determine the relationship between the suppression of appetite and energy intake by protein with ‘intragastric’ and ‘small intestinal’ mechanisms.

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