Ageing is associated with reduced appetite and energy intake (EI), termed the anorexia of ageing. In older adults, both low body weight and weight loss are strong predictors of poor outcomes, including pathological undernutrition, sarcopenia, reduced functional capacity, and frailty Rolland et al., (2011). However, the mechanisms underlying the anorexia of ageing are not fully understood. Cross-sectional studies in young adults demonstrate positive associations between EI and fat-free mass (FFM), seemingly mediated by resting metabolic rate (RMR) (Hopkins et al., (2016). Longitudinally establishing a causal effect is crucial for older adults experiencing loss of appetite due to the viscous cycle between appetite, EI, and weight reduction, predominately in FFM. This work aimed to 1) quantify differences in appetite and EI between healthy older and younger adults, 2) assess the acute effects of resistance exercise on appetite and EI, and 3) manipulate body composition through resistance exercise and protein supplementation to assess the effect on appetite, EI and, RMR in older adults.

A meta-analysis quantified differences in concentrations of appetite-related hormones, subjective appetite, and EI between healthy older and younger adults. Data from 713 young (28±7 years) and 710 older adults (73±5 years) were included based on inclusion criteria. All work followed PRISMA guidelines. Analysis revealed significantly higher concentrations of leptin [Fasted: SMD 1.23 (0.15, 2.30), p=0.025; Postprandial: SMD 0.62 (0.23, 1.01), p=0.002], insulin [Fasted: SMD 0.24 (−0.02, 0.50), p=0.073; Postprandial: SMD 0.16 (0.01, 0.32), p=0.043], CCK (Fasted: SMD 0.41 (95% CI 0.24, 0.57); p<0.001); Postprandial: SMD 0.41 (0.20, 0.62); p<0.001)and postprandial PYY [SMD 0.31 (−0.03, 0.65); p=0.075] in older adults compared to young adults. In accord, subjective hunger [Fasted: SMD −1.00 (−1.54, −0.46), p<0.001; Postprandial [SMD −0.31, (−0.64, 0.02), p=0.064] and EI were significantly lower in older adults [SMD −0.98 (−1.74, −0.22), p=0.011]. In subsequent studies, 54 individuals (23 males and 31 females) over 60 years volunteered to participate. Both studies received ethical approval. Resistance exercise led to significant reductions in subjective appetite (49 ± 8 mm h⁻¹ vs. 52 ± 9 mm h⁻¹, p=0.007, d=0.27) however appetite profiles converged with the control condition within one hour. Additionally, ad-libitum EI was unaffected two-hours post-exercise (RE = 681 ± 246 kcal; CON = 673 ± 235 kcal; p=0.865). Finally, 12-weeks resistance exercise and protein supplementation in older adults resulted in significant increases in FFM (+1.2 kg; p=0.002), postprandial subjective appetite (+8 mm; p=0.027), ad libitum EI (+119 kcal; p=0.012) and daily EI (+133 kcal; p=0.010) compared to the control. The increases in ad libitum EI correlated with increases in FFM (r=0.527, p=0.001), attributing 54% of the change in EI to FFM changes. In conclusion, FFM increases were associated with increased ad libitum EI and postprandial appetite in older adults, although no differences were observed in RMR, leptin, insulin or PYY concentrations.

Older adults experience dysregulated appetite leading to suppressed EI, which can be attenuated with a combined diet and exercise lifestyle approach. More work is required to identify the underlying mechanisms.