Every person has their own circadian rhythm, which can be divided into sleep and wake phases and is adapted to the change from day to night. Chronobiology deals with such biological rhythms, which can also be found in the organs: each organ is particularly active at a certain time of day. Artificial light – whether electric or from screens – strongly influences these rhythms, especially the sleep rhythm. This promotes the development of insomnia, chronic fatigue, but also overweight and obesity. Shift work also has a negative impact on health. In 2007, it was even classified as possibly carcinogenic by the International Agency for Research on Cancer [1].
It has long been known that healthy eating is not only about what you eat, but also when you eat. For example, irregular meals, but also consistently late meals, can increase the risk of overweight and obesity. This topic is addressed by the field of research known as "chrono-nutrition", which investigates how irregular eating, the number of meals and the actual time of food intake affect eating behaviour and thus health. Many metabolic processes take place during sleep. As these restorative activities are essential for health, scientific interest in the relationship between sleep and eating habits has grown significantly in recent years. The publication by Pot (2018) summarises numerous reviews on this topic [1]. Some important findings are discussed here.
Interaction between sleep and nutrition
People who sleep less (5 to 6 hours per day vs. 7 to 8 hours per day) often eat a less balanced diet, which is associated with a lower intake of fibre and protein. This is probably because when we are tired, we tend to reach for ready-made products or simply eat whatever is available without thinking. Normal sleep duration, on the other hand, is associated with a higher intake of certain nutrients such as vitamin C, fibre and iron. In addition, it has been shown that sleep deprivation can lead to an increased energy intake of up to 400 calories per day – particularly through the increased consumption of high-fat foods. Conversely, diet also influences sleep: irregular meals are associated with poorer sleep quality. Sleep quality also suffers when people eat a lot of sweets and pasta but few vegetables and fish.
Influence of meal timing on nutrition and sleep
There is currently no clear evidence to support the claim that breakfast is the most important meal of the day. However, there is a clearer consensus when it comes to eating late: people who eat late in the evening and eat too much have an increased risk of obesity, metabolic syndrome and cardiovascular disease. This also includes snacking while watching television. This risk is particularly pronounced when more than 25% of daily calories are consumed after dinner – a pattern also known as "night-time eating syndrome".
Discussion
The review shows a complex interplay between sleep, nutrition and health. During sleep, rebuilding processes take place: the metabolism is active, substances are broken down and rebuilt. During this time, the metabolism can work "at rest". The waking phase, on the other hand, is characterised by processes of consciousness and perception that require energy and are therefore more degrading. If you spend too much time looking at screens at night and don't get enough sleep, the forces in your organism cannot have a sufficiently restorative and health-promoting effect. This, in turn, is the basis for the waking phase. It is not without reason that people say "sleep yourself healthy" or "sleep is the best medicine". This illustrates how essential sleep and a balance between the waking and sleeping phases are. Many people are familiar with the feeling of when this balance is disrupted: stress, shift work or unhealthy habits such as watching television late into the night can lead to a lack of sleep. A lack of sleep then means you don't have the energy to prepare fresh and balanced meals. Instead, you pop a ready-made pizza in the oven or quickly eat a bar between meals to compensate for your tiredness. If you are also trying to lose weight, the increased release of the stress hormone cortisol causes you even more stress – it's almost impossible.
With sufficient sleep, on the other hand, it is easier to lose weight because the metabolism has had enough time to be active: for example, the hormone leptin, which is responsible for the feeling of satiety, is produced in sufficient quantities. Overall, it is also easier to eat more healthily. You have enough energy to cook more balanced meals, prepare fresh food and eat more regularly. A regular meal pattern ensures that the body is stimulated evenly and supplied with energy and vital nutrients. In addition, regular meals usually go hand in hand with a more structured daily routine, which means that you also go to bed at regular times. Having a regular eating and sleeping pattern brings order to everyday life, which is the basis for well-being. When these rhythms are in harmony, good health is possible.
Bibliography
[1] Pot GK (2018): "Sleep and dietary habits in the urban environment: the role of chrono-nutrition" Proc Nutr Soc. 77(3):189-198. doi: 10.1017/S0029665117003974.
