Physiological studies of whey protein in older people, with a focus on feeding behaviour, nutrition, obesity, type 2 diabetes mellitus and post-prandial blood pressure
Australia’s population is ageing. Health problems are more prevalent in elderly than younger people, and lead to much of the health expenditure and health resource allocation in this and other countries. Nutritional problems are common in the elderly and often contribute to the development and worsening of health problems in older people. A particular problem is the interacting effects of under-nutrition, reduced dietary protein intake, anabolic resistance to dietary protein (the need for greater intakes to produce the same benefits, particular on muscle mass and function) and consequent muscle loss, reduced function, and in some cases the development of sarcopaenia. Both type 2 diabetes (T2D) and obesity are prevalent in older people – and often coexist. Dietary measures are key to the management of both conditions, in older as in younger adults. Protein supplements either alone or in combination with other macronutrients are increasingly recommended to, and used by, older people, to prevent and/or manage these problems. Whey protein is often used alone or as part of these supplements, as it is has particularly beneficial effects on muscle anabolism. There remain gaps in our knowledge of the effects of whey protein ingestion in older people. This thesis comprises clinical studies designed to fill some of those gaps. The studies in this thesis from five clinical trials involved assessing responses to oral whey protein ingestion particularly whey protein concentrate on feeding behaviour, nutrition, obesity, T2D and blood pressure (BP) in older and younger people with a focus on older people. Dietary protein supplementation may play a role in the management of these conditions. The principal outcomes assessed were appetite; food intake; gut hormone release; gastric emptying rate; circulating glucose, glucagon and insulin concentrations; BP and heart rate (HR). Chapter 1: Introduction focusses on rising burden of ageing in Australia and other developed countries; nutritional problems and adverse body composition changes associated with ageing i.e. undernutrition and sarcopaenia; nutritional management of under-nutrition and sarcopaenia with a focus on the effects of whey protein; rising rates of obesity, T2D and BP effects in older people and whey protein as a management strategy; gastric emptying and its effects in older people. Chapter 2 is a review of the current literature relating to the use of protein supplements in the elderly, dietary protein requirements in older people, and the effects of ageing on the gastrointestinal responses to protein ingestion. Chapter 3 describes the effect of differing whey protein loads (control, 30 g whey protein and 70 g whey protein) before breakfast on appetite and food intake at subsequent breakfast, lunch and dinner in healthy younger and older men. Energy intake was suppressed by whey protein drinks in a protein load-responsive fashion at breakfast and particularly, at lunch, but not at dinner, and suppression of energy intake by protein was less in healthy older than younger men. Cumulative protein intake was increased in a protein load responsive fashion. These findings support the use of whey-protein drink supplements in healthy older patients who aim to increase their protein intake without decreasing their overall energy intake (ACTRN12618000881235). Chapter 4 describes the effect of whey protein load on energy intake, appetite and gastric emptying in young and older, obese men. The 30 g whey protein drink did not suppress appetite or energy intake in obese younger or older men suggesting that obesity may blunt/abolish the age-related effect of whey protein on suppression of energy intake (ANZCTR12616001216404). Chapter 5 describes the effects of co-ingesting whey protein and glucose alone and combined (a drink containing either 30 g glucose, 30 g whey protein, 30 g whey-protein plus 30 g glucose or control) on blood glucose, plasma insulin and glucagon concentrations in healthy younger and older men. The addition of 30 g of whey protein to 30 g of glucose in drink form substantially attenuated the increase in blood glucose concentrations induced by glucose alone; the magnitude of the whey-induced reduction in blood glucose was not affected by age, with comparable reductions in older to those in younger adult men; the stimulation of plasma insulin concentrations by whey protein was not reduced by ageing, unlike the insulin response to glucose; whey protein suppressed hunger less in older than younger men. Glucagon concentrations were unaffected by age. These results demonstrate that the ability of whey-protein to reduce carbohydrate-induced postprandial hyperglycaemia is retained in older men and that protein supplementation may be a useful strategy in the prevention and management of T2D in older people (ACTRN12619000420145). Chapter 6 describes the effects of co-ingesting whey protein and glucose alone and combined (a drink containing either 30 g glucose, 30 g whey protein, 30 g whey-protein plus 30 g glucose or control) on blood glucose, plasma insulin and glucagon concentrations in older men with (not on injectable treatment) and without T2D. The addition of 30 g of whey protein to 30 g of glucose in drink form substantially attenuated the increase in blood glucose concentrations induced by glucose alone; the magnitude of the whey-induced reduction in blood glucose was not affected by the presence of T2D and the stimulation of plasma insulin concentrations by whey protein. The ability of whey-protein to reduce carbohydrate-induced postprandial hyperglycaemia is retained in men with T2D (ACTRN12619000420145). Chapter 7 describes the effects of age on BP and heart rate responses to whey protein in healthy younger and older men after oral ingestion of 0 g and 70 g whey protein. The older men exhibited a greater fall in SBP after whey-protein versus control than the younger men, with no BP change after the two drinks in younger men. The nadir in SBP occurred later in the older than younger men with SBP still apparently declining 180 min after whey-protein ingestion in the older men. The magnitude of the rise in HR was greater in the younger men indicating that following ingestion of 70 g whey protein, healthy older men exhibited a sustained fall in BP, despite an increase in HR, whereas in younger men there was no change in BP. BP may need to be monitored after high protein meals in older people at risk of postprandial hypotension (ACTRN12612000941864 and ACTRN12614000846628). Chapter 8 describes the BP and heart rate responses to oral protein intake in healthy older men after ingestion of 30 g and 70 g of whey protein. The older men exhibited a decrease in systolic blood pressure (SBP) after ingestion of 30 g and 70 g of whey protein to a similar degree after both the drinks and greatest between 120 and 180 mins after ingestion. HR was increased maximally after 70 g particularly in the third hour (hr) and diastolic blood pressure (DBP) decreased non significantly after protein drinks. Even modest protein loads in older men can result in postprandial hypotension (PPH) and care must be taken (ACTRN12612000941864). Chapter 9 describes the acute effects of whey protein, alone and mixed with other macronutrients in varying amounts such as 70 g whey-protein (P280); (ii) 14 g whey-protein, 28 g carbohydrate, 12.4 g fat (M280); (iii) 70 g whey-protein, 28 g carbohydrate, 12.4 g fat (M504); or (iv) a non-caloric control drink (C) on BP and heart rate in healthy older men. SBP decreased after all three nutrient drinks with the greatest reduction after the M504. Maximal decreases in SBP occurred about 2 hr after drink ingestion and were sustained thereafter. Maximum DBP decreases and HR increases occurred after M504, with no differences between the effects of the P280 and M280 drinks, thereby demonstrating that the effects of whey-protein containing drinks to lower BP and increase HR appear to be primarily dependent on their energy content rather than macronutrient composition and may persist for at least 3 hr after ingestion. Pure whey-protein drinks may represent the best approach to maximize protein intake without increasing the potential for deleterious BP falls in older people (ACTRN12614000846628).
Whey Protein, Ageing, obesity, type 2 diabetes, post-prandial blood pressure, gastric emptying
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