Food is often seen as one of the primary influences on our health. However, it is often overlooked that when we eat can be just as important as what we eat. Researchers found out that our circadian rhythm is closely linked to our metabolism, opening the door to a whole new research area: Chrononutrition.
The underlying principle of chrononutrition: Our body wants to optimize our behaviour according to time of day. If our feeding and fasting times are aligned with clock-regulated metabolic changes, our digestion can be improved. Appropriate nutrition, so aligning when we take up energy to when we actually spend it helps to maintain a healthy circadian rhythm.1 Otherwise, our organs are pretty quick to react to time-shifted food intake by changing their metabolism.
Whether our primary circadian rhythm in the brain (in the Superchiasmatic Nucleus) can be changed in any way by food intake is still subject to research. In one study, healthy young men ate only in the morning vs. only in the evening, and the first group’s circadian rhythm (core body temperature and heart rate) was advanced after three days.2The relationship nutrition – circadian rhythm is not unidirectional: Vice versa the circadian rhythm also strongly influences our eating habits. The gastric emptying and the speed of congestion peaks in the morning hours.3 Mice that were fed in a rest phase gained more weight than those fed in an active phase.4 Other studies on animals have shown that feeding at the wrong time may even contribute to chronic disease developments or less fertility. These adverse effects can be minimized by a fixed food schedule. It has been shown that eating only at restricted times can help for example with obesity – so the success of the trending 16:8 (fasting 16 hours, having ones meals withing 8 hours of the day) can actually be explained by chronobiology.5
There are several compounds that are proven to act on the circadian rhythm:
- Alcohol seems to be particularly disruptive to the circadian rhythm in humans and other animals.6
- Caffeine, while delaying our inner clock when consumed in the evening, can for instance speed up synchronization to new time zones when having a jetlag.7 However, there is no evidence that two cups of coffee in the morning might help with circadian disorders: In a study with blind participants that had a non-24h inner clock, caffeine was insufficient to entrain circadian rhythms.8
- Specific compounds and their effects on circadian rhythm are starting to be investigated. Some studies already present promising results, for example an aminoacid called L-serine has been found to enhance the effect of bright light in the morning.9
Circadian phase advancement by bright light one day after intake of L-serine in comparison to a placebo drug. In this study intake of L-Serine nearly doubled the effect of bright light therapy. [Yasuo 2009]
 Chaix A, Zarrinpar A, Miu P, et al. (2014) Time-restricted feeding is a preventative and therapeutic intervention against diverse nutritional challenges. Cell Metab 20, 991–1005.
 Krauchi K, Cajochen C, Werth E, et al. (2002) Alteration of internal circadian phase relationships after morning versus evening carbohydrate-rich meals in humans. J Biol Rhythms 17, 364–376.
 Buhr ED, Yoo SH & Takahashi JS (2010) Temperature as a universal resetting cue for mammalian circadian oscillators. Science 330, 379–385.
 Arble DM, Bass J, Laposky AD, et al. (2009) Circadian timing of food intake contributes to weight gain. Obesity (Silver Spring) 17, 2100–2102.
 Oike, Hideaki, Oishi, Katsutaka, and Kobori, Masuko. “Nutrients, Clock Genes, and Chrononutrition.” Current Nutrition Reports 3.3 (2014): 204-12. Web.
 Huang MC, Ho CW, Chen CH, et al. (2010) Reduced expression of circadian clock genes in male alcoholic patients. Alcohol Clin Exp Res 34, 1899–1904.
 Burke TM, Markwald RR, McHill AW, et al. (2015) Effects of caffeine on the human circadian clock in vivo and in vitro. Sci Transl Med 7, 305ra146.
 St Hilaire MA & Lockley SW (2015) Caffeine does not entrain the circadian clock but improves daytime alertness in blind patients with non-24-hour rhythms. Sleep Med 16, 800–804.
 Shinobu Yasuo et al, L-Serine Enhances Light-Induced Circadian Phase Resetting in Mice and Humans, (2009) 17, 2100–2102. doi:10.1038/oby.2009.264