The idea of circadian rhythms is often associated with sleep and wake cycles, but, in reality, they regulate several distinct behaviors, including feeding behavior. At Loyola University Chicago, a team of researchers manipulate the “molecular clocks” found in Drosophila or, as we might know them, common fruit flies and observe the resulting feeding behavior. They report their findings in the paper “Central and Peripheral Clock Control of Circadian Feeding Rhythms” by Fulgham et al.
The molecular clocks they describe are composed of the following: The main genes involved in this system are called period (per) and timeless (tim) and produce the proteins PER and TIM accordingly. CLOCK and CYCLE are transcriptional activators, basically, factors that regulate these genes and the production of PER and TIM. In a day, these proteins accumulate and degrade and their levels in the body regulate the body’s functions. These molecular clocks function both in the central tissues such as the brain and peripheral tissues such as, in this study, fat bodies (functioning as energy storage in insects).
Fulgham and the team disrupted the molecular clocks in the central and peripheral tissues of the fruit flies by manipulating the per or tim genes. They found that disruption in the central tissues led to profound disturbances in feeding, both in rhythm and appetite, whereas disruption in the peripheral tissues mainly impacted the strength of feeding. While peripheral tissues still play a role in feeding behavior, central tissues are what set the pace for feeding behavior. It is imperative for feeding behaviors that molecular clocks are functional.
Like in fruit flies, circadian rhythms interact with and regulate the timing of digestive functions and eating habits. However, humans can consciously control when to eat despite hunger or cues from molecular clocks, and environmental factors can strongly influence this decision–work, school, convenience, etc.
In a scientific review published by Parr et al., previous studies are used to discuss how people should time eating and exercise in a way that is considerate of the cycles and rhythms inherent to our bodies. In order to understand how circadian rhythms impact human metabolism, we can look to insulin. Insulin secretion and sensitivity are elevated earlier on in a day and decrease over time, being relatively lower in the evenings. Eating meals that are likely to spike one’s sugar levels earlier on in the day can take advantage of this.
This review mentions dieting interventions that are meant to help regulate weight–however, these interventions are designed around obesity and metabolic disorders that focus on weight loss as part of the treatment, and therefore are not applicable to everyone and their specific health goals. The intervention of interest here is called time-restricted eating (TRE) and maintains the common thread of circadian rhythms and their impact on metabolism. Studies on this strategy would ask participants to limit the timing of their meals to a 10 hour window per day. While some studies reported weight loss, others focused on how they affected health markers–in one study TRE was found to positively impact the sugar levels of those with type 2 diabetes.
While there are many other significant factors that impact human health, eating habits and circadian rhythms are deeply intertwined and are worth further study. When it comes to molecular clocks outside of human health, it is important to uncover the mechanisms around these clocks in order to add to our understanding of biological pathways and how they interact.
References
Fulgham, C. V., Dreyer, A. P., Nasseri, A., Miller, A. N., Love, J., Martin, M. M., Jabr, D. A., Saurabh, S., & Cavanaugh, D. J. (2021). Central and Peripheral Clock Control of Circadian Feeding Rhythms. Journal of biological rhythms, 36(6), 548–566. https://doi.org/10.1177/07487304211045835
Parr, E. B., Heilbronn, L. K., & Hawley, J. A. (2019). A Time to eat and a time to exercise. Exercise and Sport Sciences Reviews, 48(1), 4–10. https://doi.org/10.1249/jes.0000000000000207
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