Cameron- Smith, DPoppitt, SMilan, Amber2015-12-1420152015http://hdl.handle.net/2292/27754With the elderly representing a growing segment of the population, their heightened morbidity and mortality are of great public health concern. Despite the rapid gains in medical knowledge and treatments, older adults are more likely to experience chronic illnesses that can decrease quality of life or accelerate mortality. Nutrition is a key modifiable lifestyle factor which greatly impacts chronic disease risk. With ageing, macronutrient processing and immune system function may alter both the digestive and absorptive responses to food and the elicited immune responses. These changes may be instrumental in the development of age-related metabolic diseases. Surprisingly, the digestive responses of older adults are not well characterised. Given the importance of digestive capacity and the impacts on metabolic and immune outcomes, this thesis aimed to examine the post-meal protein, lipid, and inflammatory responses to complex meals in older adults. The particular focus is to examine the impact ageing exerts on protein digestion, focusing on the appearance of amino acid in circulation. Secondly, the chylomicronaemic response is examined through the appearance of exogenous lipids in circulation. Thirdly, the inflammatory responses to high fat and low fat meals are examined in older adults. Muscle loss in ageing (sarcopenia) contributes to morbidity and mortality in the elderly. This muscle loss in part stems from impaired protein synthetic responses to ingested proteins and amino acids. Protein digestion in response to whole meals in the elderly is inadequately described. In response to a mixed meal, older adults demonstrated no difference in total amino acid appearance in circulation. However, older adults had delays in serum total, essential, and branched-chain amino acid appearance after a high protein, low fat meal. The magnitude of age-related delay in amino acid appearance was reduced following a high protein, high fat meal, likely attributable to differences in digestibility and glycaemic responses evoked by the meal structure and composition. These findings demonstrate the impact of a mixed meal on protein digestion in older adults and implicate a role for meal composition and design in the nutritional support of muscle maintenance in older adults. Cardiovascular disease affects older adult at increased rates, and is contributed to by postprandial lipaemia and inflammation. Detailed studies of the post-meal dynamics and composition of chylomicrons examined these aspects in response to mixed meals. The aims were to analyse the size and fatty acid differences in older adults’ chylomicrons. Older adults had exaggerated and prolonged postprandial lipaemia, but elevated triacylglycerols were not attributed to the chylomicron fraction; this was particularly apparent after a low fat meal which provoked endogenous TAG elevation in older adults. Older adults had smaller, more numerous chylomicrons containing greater proportions of MUFA and less PUFA in the TAG and PL fractions, although specific age differences in TAG fatty acids varied depending on meal composition. These data establish the altered dynamics and composition of older adults’ chylomicrons, and illustrate the importance of endogenous TAG contributions to elevated postprandial lipaemia in the elderly. The systemic low-grade inflammation that contributes to chronic disease is fueled by post-meal inflammatory responses. The elderly have altered metabolic and immune function, which is known to contribute to this proinflammatory state in younger adults. Yet postprandial inflammation has not been described in older adults, which was therefore an aim of the study. The activation of immune responses by ingested lipids, bacterial translocation, and oxidative stress were examined in older adults following high and low fat meals. Older adults demonstrated baseline inflammatory gene and protein expression indicative of age-typical cellular senescence and inflammaging. Yet the immune activation by lipoproteins and translocated endotoxin was no different between older and younger adults. However, baseline and postprandial antioxidant capacity may differ in older adults, although this does not appear to transiently affect immune activation. A high fat meal triggered greater circulating concentrations of cell-free DNA in younger adults, detected for the first time as a potential transient marker of acute stress responses to feeding. These findings demonstrate that immunosenescence in older adults does not allow for detrimental postprandial immune activation in metabolically healthy individuals. This suggests that healthy ageing preserves appropriate immune responsiveness to feeding. Importantly, this thesis demonstrates that older adults have preserved protein and lipid absorption, but that the kinetics of these responses differs from younger adults. Delayed appearance of amino acids may have implications for stimulations of the muscle protein synthetic response to feeding. Additionally, differences in chylomicron formation may contribute to altered lipaemic clearance following a meal, but endogenous lipoprotein production may be an equally important factor. Furthermore, this thesis shows that immune responses are preserved in the healthy elderly, and do not likely contribute to a heightened post-meal inflammatory response. Notably, both protein and lipid digestive responses may be responsive to modifications of meal composition and structure.Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher.https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htmhttp://creativecommons.org/licenses/by-nc-sa/3.0/nz/ThesisCopyright: The Authorhttp://purl.org/eprint/accessRights/OpenAccessQ112200854