The impact of protein and probiotic supplementation on appetite and energy intake in older adults

It is projected that in the next decade, older adults will make up one quarter of the world population (WHO, 2019). The general increase in the standard of living in the developing world coupled with inherent physiological changes associated with ageing puts into question how older adults can reverse age-related muscle mass loss, also known as sarcopenia, and therefore maintain their independence. Exercise and appropriate nutrition, especially adequate protein and energy intake (EI), are considered the optimal strategies to limit age-related declines in muscle mass and function. Age-related changes in appetite regulation may also have a profound effect on food intake and older adult nutrition. These include a reduction in appetite and taste, slower gastric emptying, and changes in appetite-regulating hormones, which create a challenge in assisting to increase dietary intake in older adults. When combined with adverse psychological and social aspects of aging, many older adults are susceptible to developing sarcopenia, malnutrition, and obesity as a consequence of dysregulated appetite. One strategy that may be a useful prevention strategy for sarcopenia is protein supplementation. However, since protein is well known to be a satiating macronutrient, it is important to investigate what type of effects protein supplementation may have on overall energy intake (EI) and appetite in older adults over 60 years of age. In Chapter 2, the existing literature was systematically reviewed with meta-analysis in both acute (n=9) and longitudinal studies (n=13) to investigate the effects of protein supplementation on appetite and EI in older adults. Evidence from (n=22) studies (n=857 participants) concluded that although appetite ratings and related peptides may be suppressed under some conditions, protein supplementation does not compromise EI in this population. Protein supplements in all forms appear to be effective in increasing EI acutely in healthy older adults. Results from this meta-analysis supported the use of protein supplementation in older adults without compromising EI. Chapter 3 reports results from a double blinded randomized cross-over pilot study where 12 participants underwent an 8-week probiotic or placebo supplementation period and a plant protein only diet to establish the effects of BC30 (vegetable protein derivative) probiotic on energy intake, appetite, and appetite hormone PYY in older adults (n=12). The aim was to test the hypothesis that a probiotic derivative would improve energy intake as well as appetite during a controlled plant protein only diet in older adults. Contrary to the hypothesis, results from this study showed that probiotic supplementation significantly decreased appetite in the older adults and had no overall impact on energy intake or appetite-related hormone PYY. The results from this thesis support the use of protein supplementation as an effective strategy for preventing muscle mass loss in older adults without compromising daily intake, and suggest that probiotic supplementation is not an effective strategy for increasing appetite during a plant only diet in older adults.