In part one of our blog, we defined circadian rhythm and outlined its connection to sleep health, as well as the factors that can influence it. Can the gut microbiome play a role – and what mechanisms could provide answers?

Click here to read the first instalment.

Does the gut microbiome have a role in improving sleep?

High gut microbial diversity is associated with sleep efficiency and increases in pro-inflammatory cytokines are associated with reduced sleep quality. Gut bacterial diversity with diverse species from Bacteroidetes, Actinobacteria and Firmicutes, produces metabolites that benefit the gut-brain axis by producing γ-aminobutyric acid (GABA), a neurotransmitter that is thought to promote sleep1. Since there is an association between greater gut microbiome diversity and improved sleep quality, there could be a future for modulating or modifying it to improve sleep quality.

Interestingly, food or nutrition, as a stimulus for the circadian rhythm, can be as influential as the light-dark cycle. Several factors can have an effect, including the types of food and nutritional content, as well as frequency and timing of consumption. Demonstrating the connection, short sleep duration has been associated with a higher probability of snacking throughout the day, eating across a longer period of the day and poorer quality of diet2.

The production of Short Chain Fatty Acids (SCFAs) by the gut microbiome comes from the fermentation of non-digestible dietary components, such as fibre. It is evident that SCFAs can affect the brain, seen in anxiety, depression and now circadian rhythm too3. SCFAs produced after a meal, for example at breakfast, enhance the phase change of the circadian rhythm. The phases are the peaks and troughs of performance across the 24 hours in a day. High fibre diets increase bifidobacteria and SCFA production, which increase the speed of the modification between phases of circadian rhythm. There is a change in pH in the colon and production of metabolites, including SCFAs from the fermentation of fibre, which contributes to metabolic functions, immune modulation and the modulation of the circadian rhythm3.

Host diet is an important core element for encouraging the gut microbiome to thrive. Beneficial butyrate-producing bacteria are carbohydrate-degrading bacteria that benefit from a high plant-based fibre and polyphenol rich diet. Diets rich in prebiotic galactooligosaccharides have been known to increase beneficial bacteria and as a result, reduce the impact of stressor-exposure to the gut microbiome and strengthen the sleep/wake cycle in circadian rhythm4.

Manipulating the gut microbiota through diet could be beneficial for the circadian rhythm, therefore for sleep quality and quantity, since it is known to be a factor.

How does circadian rhythm affect the gut microbiome?

While the brain and the SCN alter the circadian rhythm when triggered by light, there are peripheral receptors of the circadian cycle that can be triggered by food, temperature and other factors. The feeding regime and eating patterns are important for the peripheral circadian rhythm receptors4. Eating patterns affect the rise and fall in the circadian rhythm. Energy intake, nutrient composition and timing of meals can cause changes to the phases of circadian rhythm, and there can be an effect in the other direction as well.

It is well known that a change in diet, even over a matter of just a few days, can alter the composition of the gut microbiome. The periods of time between food consumption are just as important for the gut microbiome as time spent eating, in terms of the total gut microbiota composition. Fasting time between meals provides the optimal environment for some beneficial bacteria to thrive, whereas other beneficial bacteria require an environment with products of digestion in order to proliferate4.

In Summary

It appears that there is a multi-directional relationship between the gut microbiome, circadian rhythm, diet and other environmental factors.

With the metabolic and immunological associations, it seems reasonable to suggest that more research focuses on the diet and gut microbiota mechanisms in circadian rhythm disruption for health. In turn, this may point towards the gut microbiome’s potential as a route of approach when addressing the improvement of sleep health.

During winter as daylight cycles become shorter, it provides a prime opportunity to think about dietary patterns and physical activity during light to prevent circadian rhythm disruption. Further research is required to guide interventions but dietary factors are certainly something to consider given their influence on the gut microbiome.

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