Abstract/Summary

Ageing is often accompanied by a decrease in appetite and physical activity (PA), which may lead to malnutrition resulting in decreased muscle mass and physical capabilities. To preserve muscle mass, older adults are advised to increase protein intake and PA. However, there is evidence suggesting protein may have a greater impact on satiety than carbohydrate or fat, which may cause reduced energy intake (EI). PA is also recommended by organisations and charities such as NHS and Age UK to enhance older adult’s appetite; however, there is insufficient research to support this advice. In Chapter 2, the effects of different macronutrients on appetite, EI, and gastric emptying (GE) in younger and older adults were investigated. EI was assessed by an ad libitum meal, appetite was assessed using 100 mm visual analogue scales, and gastric emptying was measured via the 13C-octanoic acid breath test. Neither the macronutrient type nor age significantly affected appetite, EI, or GE. In chapter 3, a cross-sectional study examined the association of PA with EI and appetite in older adults. Participants were divided into tertiles (low, medium, high), based on PA levels (PALs) measured by a wrist-worn accelerometer and, activity energy expenditure (AEE) and total energy expenditure (TEE) evaluated with simplified PA diaries recorded for seven days. EI was assessed by 3-day weighed food diaries and appetite was evaluated using 100 mm visual analogue scales 30-minute intervals over a single day. Diet quality was calculated using the Nutrient and Food-based Diet Quality Index-65. The high AEE and TEE groups had a higher protein intake, while higher PA was linked to a higher desire to eat. In chapter 4, the relationship between the PALs, AEE, TEE and diet quality were investigated using the same cross-sectional study data. While there was no significant difference in diet quality scores between the groups, the high AEE group had greater protein diet quality component scores. In chapter 5, appetite, EI, and GE responses to protein in older adults with different PALs were compared with a home-based study. EI was assessed by an ad libitum meal perceived appetite was determined using 100 mm visual analogue scales, and gastric emptying was measured via the 13C-octanoic acid breath test. Higher protein intake did not affect appetite but decreased EI and slowed GE. Additionally, higher PA was found to decrease appetite and accelerate GE. The findings showed that higher protein intake had no immediate effect on perceived appetite (from VAS scales) within a three-hour timeframe but may influence EI in an at-home setting. While higher PA was found to decrease appetite within a three-hour timeframe, cross-sectional findings showed a link between higher PA and higher desire to eat food within a twelve-hour timeframe, along with a link between higher TEE and higher EI, indicating the potential role for PA in increasing appetite and energy intake in older adults.