Loss of appetite is frequently observed during ageing; termed the ‘anorexia of ageing’. Some evidence suggests that with advancing age there is an increase in satiety hormones, such as CCK and PYY, and a decrease in the hunger hormone ghrelin which may contribute to the anorexia of ageing. However, not all studies agree, emphasising the need for more in depth research to clarify age related changes.
My first study developed a rat model to replicate the hormonal responses observed in humans. However, the results of this study did not replicate human studies; there were no alterations gastrointestinal hormones. I then designed a human study to examine more comprehensively, the effect of ageing on gastrointestinal peptide hormone release. Healthy human volunteers aged 20 to 92 years were studied in fasting and post-prandial conditions. The results demonstrated an increase in PYY concentrations post-prandially in older volunteers. In order to understand the mechanism behind this, I followed this study with an investigation looking at the changes in gastrointestinal hormones in ageing mice colons. The data produced results conflicting with the human study, since no increase in PYY levels was observed.
Dietary manipulation provides a good opportunity to alter gastrointestinal appetite hormone release, since release differs depending on the macronutrient content of the food consumed. My final studies focused on high protein diets. Results demonstrated that older volunteers were insensitive to the satiating effect of protein, where younger volunteers ate less following a high protein test meal but the older volunteers food intake did not change. Gastrointestinal appetite hormones concentrations did not change significantly between the high and low protein meals in the older and younger adults.
These results suggest that age-associated reductions in appetite could be due to a resultant increase in the satiety hormone PYY. More studies need to be conducted to understand the role of protein on appetite and food intake in older adults
