Intermittent Energy Restriction and Chewing on Neural Stem Cell Ageing and Adult Hippocampal Neurogenesis Associated Cognition

Nutrition and human health are strongly related. Altering overabundance through fasting/calorie-restricted diets has profound effects on homeostasis, tissue regeneration, and cancer. Tissue stem cells respond to the physiological changes that occur during fasting through dynamic shifts in their metabolism. Restricting energy intake in mice or introducing mutations in nutrient-sensing pathways can extend lifespans by as much as 50%. Post-mortems reveal that tumours, heart problems, neurodegeneration and metabolic disease are generally reduced/delayed in long-lived mice. Therefore, extending lifespan by energy restriction (ER) also seems to increase 'healthspan', the time lived without chronic age-related conditions. These insights have hardly made a dent in human medicine. Molecular and cellular insights should be established in humans to validate interventions such as ER to delay ageing and associated conditions e.g. cognitive decline (Murphy et al., 2014).

Stem cells from the central nervous system also respond to ER. Recently, the Thuret lab have found that ER, in the absence of malnutrition, promotes hippocampal stem cells to proliferate and differentiate into new-born neurons. Because these new postnatal hippocampal neurons have been shown to play a role in cognition, ER also promoted enhanced cognition in rodents (Zainuddin et al., 2012; de Lucia et al., 2017; Thuret et al., 2012). This phenomenon of neurogenesis, the process by which new neurons are generated from neural stem cells, is also occurring in humans (Spalding et al., 2013). It is a tightly regulated process occurring in the mammalian hippocampus which is an environmentally responsive brain structure known to regulate learning, memory and mood. Proposed functions of adult hippocampal neurogenesis (AHN). include enhancing recognition memory, the ability to recognise previously encountered stimuli, and pattern separation, the ability to differentially encode small changes in similar inputs (Clelland et alk., 2009; Sahay et al., 2011). It has been posited that calorie restriction may increase neurogenesis as a "cellular relic" of intermittent feeding patterns during evolution as a response to alternating periods of famine and abundant food (Murphy \& Thuret, 2015). Human trials have found significant improvements in verbal recognition memory after 30% reduction in calorie intake (Witte et al., 2009). Also, intermittent fasting in humans has been associated with significant increases in brain activation volume in areas involved in brain function control and plasticity(Belaïch et al., 2016). Food texture and mastication have also been implicated in AHN and cognitive ability (Smith et al., 2016). Decreased mastication due to the removal of molars and edentulism in both humans and animals have a negative impact on AHN and associated cognition. Human populations, in particular, have shown a close association between masticatory function, cognitive status and age-related neurodegeneration in the elderly (Miura et al., 2003). The exact mechanism by which mastication affects cognition is unknown.

Research question: In older, overweight participants does IER and/or extended periods of mastication enhance performance inhippocampus-dependent memory tasks and increase anti-ageing marker Klotho?

Objectives:

1. A randomised controlled parallel-design trial will determine the impact of an IER diet (2 consecutive days of a very low calorie diet, 5 days of normal healthy eating for 3 months) and/or extended periods of mastication (10 minutes 3 times a day for 3 months) compared to a control group (continued habitual eating behaviour, dietary patterns) on primary outcome variables (MST and Klotho) in older, healthy participants with overweight or class I obesity.
2. To assess the impact of an IER diet and extended periods of mastication on secondary outcomes variables including body composition, mood and sleep.
3. To explore whether extended periods of mastication can be utilised as a weight loss/fasting aid.