With obesity being declared an ongoing and growing pandemic in the 21st century, researchers have been showing high interest in the biological role of our bodies which either induce, or prevent cases of obesity. As such, it has been highly beneficial to find linkage between different circadian rhythmic loops, and their effect on the body's metabolic rate. This is why the article Central and Peripheral Clock Control of Circadian Feeding Rhythms, by Carson V. Fulgham et al., is an excellent foundational study for the implications circadian feeding loops have on our feeding patterns, and on health in general.
The experiment performed by Fulgham and his team studied multiple circadian timing systems found in the fruit fly, or drosophilia melanogaster, specifically focusing on clock cells which included a circadian clock for feeding rhythms. The article explained the mechanisms of these clock cells, stating that they functioned by the oscillations in gene expression underwent during the ~24 hour periods considered the length our "biological clocks". The specific genes activated were core clock genes period (per) and timeless (tim), which were dependent on transcriptional activators CLOCK (CLK) and CYCLE (CYC) to be transcribed. The proteins are synthesized, then sent back into the cell to repress their transcriptional-driving factors CLK and CYC, marking the end of the cycle. In the study, the research team manipulated this organic system in two ways; (1) By integrating GAL4 transcription factors into the circuit to shift the phase of the feeding rhythm, and (2) by perpetuating complete hindrance of the clock cell tissues by introducing CRISPR-Cas9 to the flies' systems in order to eliminate the production of per and tim, ultimately restricting the entire function of the clock systems. Furthermore, they tested several different clock cell tissues, including brain circuits, peripheral tissue, and the fat body of Drosophilia, which mimic adipose tissue in mammals by secreting factors, such as leptin, which are directed to the hypothalamus (where the brain clock cells are mediated), ultimately inhibiting feeding. Each tissue sample was tested in order to determine what role each of them play in the feeding rhythms, if any.
The findings revealed that the circuits in the brain heavily dictated the periods, and overall occurrence, of feeding rhythms. This conclusion came about because it was found that altering the cells with dbt would slow the feeding rhythm oscillations in the brain, and sgg would speed up the oscillations. However, when the peripheral tissue and that of the fat body was tested, it showed no output on the feeding rhythms. Then again when the central brain clock was completely knocked out, arhythmic patterns emerged in the flies' feeding once again.
The implications you can draw from the conclusions of Fulgham's study are that not only are our circadian rhythm systems accountable for feeding patterns, but they are not indefinite, and can be altered, much to our benefit, as we know that we our circadian rhythm also controls events such as our metabolic activity levels, and insulin sensitivity. Therefore, it is important for us to optimize our feeding patterns so that they are in line with our bodily circadian mechanisms.
The article The Effects of Individual Circadian Rhythm Differences on Insomnia, Impulsivity, and Food Addiction, by Ali Kandeger et al., addresses the slight changes that can occur in our circadian rhythms, based on environmental stimuli, and how those implicitly effect food addiction, and obesity. The team conducts a study on college students who show behaviors of either morning type, neither type, or evening-type circadian rhythms. The paper includes connections between evening-type individuals having a slower oscillation period than morning type individuals, as well as habits such as insomnia, which leads to sleep deprivation, which is known to cause an increase in appetite and food-intake. Other habits include late-night cravings, and skipping meals, which are characteristics of individuals who are prone to developing high cholesterol, diabetes, and becoming obese. From all the previous recorded evidence, Kandeger and her team hypothesized that participants who showed evening-type circadian rhythm patterns would have indirectly developed an increase in food addiction because of a direct development of insomnia and sleep deprivation.
After performing a cross-sectional study to analyze the correlation between circadian rhythmic differences and food addiction, it was concluded there was no significant correlation between food addiction and circadian preference. However, because there was a correlation between evening-type people and insomnia/ sleep deprivation, there still exists an indirect linkage between evening-type circadian rhythms and food addiction, ultimately leading to obesity and many other health problems.
While it was discovered that our circadian clocks are not directly responsible for our habits or addictions, both studies concluded how they have a major impact on the way we process food metabolically, as well as attributes on other habits and disorders which opens the door to a web of future health problems, one of which being obesity. The studies also included scientific evidence that our internal clocks can be adjusted, whether that is via environmental stimuli, or by chemical intervention. Further studies to determine how we can optimize our circadian rhythm patterns could potentially benefit human health in many regards, such as by lowering susceptibility for obesity. Hence, both of these foundational and contemporary studies are a great starting point for the science on this topic to advance in the near future.
References
Fulgham, Carson V., et al. “Central and Peripheral Clock Control of Circadian Feeding Rhythms.” Journal of Biological Rhythms, vol. 36, no. 6, 2021, pp. 548–566., https://doi.org/10.1177/07487304211045835.
Kandeger, Ali, et al. “The Effects of Individual Circadian Rhythm Differences on Insomnia, Impulsivity, and Food Addiction.” Eating and Weight Disorders - Studies on Anorexia, Bulimia and Obesity, vol. 24, no. 1, 2018, pp. 47–55., https://doi.org/10.1007/s40519-018-0518-x.
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