Many of you will know that our dietary choices can affect the quality of our sleep. For instance, eating certain foods at night-time (malted milk, bananas) can make it easier to fall asleep, while drinking alcohol can cause sleep interruptions. But did you know that unhealthy diets may also disturb our circadian rhythm? In this blog, I will talk about a recent study with mice that showed how a high-fat diet can disturb their circadian rhythm.
A circadian rhythm is a natural, internal process that regulates when we are awake and when we are asleep. The term circadian comes from the Latin circa, meaning “around” (or “approximately”), and diem, meaning “day”. Circadian rhythms repeat themselves roughly every twenty-four hours. Every day, for instance, body temperature is highest at around 7PM and lowest around 4:30AM. Similarly, blood pressure, energy metabolism, brain metabolism, and secretion of hormones change in a highly predictable fashion each day.
Circadian rhythms are driven by a built-in ‘central clock’. In humans, the central clock is located in the suprachiasmatic nucleus (SCN), which is part of the hypothalamus, which in turn is part of the brain.
Fun fact: the SCN is located right on top of your optic nerves (running from your eyes to your brain). And for good reason: to help the central clock, your eyes contain special cells that project directly to the SCN. That way, the SCN can sense light and dark, and adjusts the central clock if necessary.
Just like a real clock, the central clock can be adjusted. A well-known example is the adjustment when travelling across time zones. Influenced by the light and temperature in one’s new environment, the central clock will – after a rather uncomfortable period of jet lag – adjust to the new time zone. Light and temperature are not the only factors that can influence the central clock, however. Did you know that your diet can also affect the settings of your central clock?
Recently, researchers compared two groups of mice. For ten weeks, one group was fed a normal diet while the other group was fed a high-fat diet. The high-fat diet resembled what one would call an ‘unhealthy diet’ for humans. After ten weeks, researchers investigated the mice brains. They found that the unhealthy diet influenced the SCN and other brain regions. Where mice that were fed a regular diet showed normal circadian rhythms in brain metabolism, the high-fat-diet group did not. This experiment shows that the central clock is indeed sensitive to what we eat.
A few caveats of this study should be kept in mind. First, just because a high-fat diet induces changes in the mouse brain, doesn’t mean that an unhealthy diet can also change the human brain. After all, mice and men are not the same. Second, we do not know whether the behaviour of the high-fat-diet mice changed. If the high-fat-diet mice didn’t show any behavioural changes (e.g. their sleep-wake cycle remained normal, they were as alert as always, etc.), despite their brains showing a different metabolism, then these brain changes might not be very meaningful. Nonetheless, the idea that our dietary choices may shape such important and automated bodily functions as our circadian rhythm is absolutely intriguing.
E.R. Kandel & J.H. Schwartz (2012). Principles of Neural Science, Fifth Edition. Chapter 51: Sleep and Dreaming.
P. Jiang, F. W. Turek (2017). Timing of meals: When is as critical as what and how much. Am.
J. Physiol. Endocrinol. Metab. 312, E369–E380.
P. Tognini, M. Samad, K. Kinouchi, Y. Liu, J.C. Helbling, M.P. Moisan, K. L. Eckel-Mahan, P.
Baldi, and P. Sassone-Corsi (2020). Reshaping circadian metabolism in the suprachiasmatic nucleus and prefrontal cortex by nutritional challenge. PNAS 117 (47)