The way you eat is key in health and illness. But not only what and how much we eat influences, but also when. In recent years, science has focused on unraveling the phenomenon of chrononutrition, which explains the relationship between temporal eating patterns, circadian rhythms and metabolic health. And some research has already shed light on the importance for the body of good synchronization of food intake times with our circadian rhythms, which are that 24-hour biological clock that regulates internal physiological functions. Scientists have found that skipping breakfast is associated, for example, with an increased risk of obesity, and eating late dinners is also linked to weight gain.
The human being has a kind of central clock that sets the time to the body. At first glance, it is barely a one-millimeter ball located in the hypothalamus, but these tiny molecular devices are capable of telling the time to the rest of the body and, together with the small tissue-independent chronometers, they anticipate and prepare the cells to what is to come, such as eating at noon or going to sleep at night. “Our body has schedules and this central clock is not isolated, but is synchronized with the outside, mainly through light and darkness, but also with changes between eating and fasting or with moments of activity and rest” explains Marta Garaulet, professor of Physiology at the University of Murcia and expert in chrononutrition.
Respecting circadian rhythms and all those biological changes that follow a 24-hour cycle is essential for health. So much so that a disruption in these biorhythms can alter basic vital functions, the scientist points out: “We are diurnal animals, we are made to sleep at night and we do not eat while we sleep. We are made to eat and move during the day. So, if your body perceives that there is light at night or that you are eating, it is receiving contradictory information.”
Through the central clock, peripheral chronometers (which are in organs and tissues), lifestyle habits, behaviors and the environment, internal biorhythms are regulated. “A person who is fine with his chronobiology is one who has all his clocks synchronized and in accordance with the changes of light and darkness,” clarifies Garaulet. Now, there may be synchronization failures in the central clock, in the peripherals or in the behaviors; and that can create chronodisruptions that, in the long run, says the scientist, “are related to diseases, such as obesity, cancer, depression or metabolic alterations. This is clearly seen in shift workers or night employees, who are an example of people whose behaviors are misaligned with their internal clock.”
Lunchtime, a synchronizer
The moment of eating, like light, is a clear modulator of internal clocks, says Garaulet. “Mealtime is a synchronizer of the peripheral clocks of food-related organs such as the liver and pancreas. If you eat at the wrong time, all the organs that prepare to receive the food do not react well: because receiving food is an impressive impact for the body and it has to prepare,” says the specialist, who goes into more detail about this explanation: “It is as if they are coming. 100 people come to eat at your house and they don’t let you know. An anticipation that food is going to enter the body helps it respond well and, when that does not happen, there is an alteration at the metabolic level.”
The body is programmed a way and the organs function accordingly. That is, in a different way during the 24 hours of the day: they do not respond the same if they have to work at a time that they had not planned. The pancreas, for example, is lazier at night and more active during the day. “Eating dinner late has a very clear effect: it coincides with the secretion of melatonin, which is the hormone that prepares you for sleep, with insulin, which is the hormone that helps distribute food. But, in the presence of melatonin, insulin secretion is reduced and tolerance to sugar and carbohydrates is worse,” says the chronobiologist. She and her team discovered a decade ago that eating late can influence your ability to lose weight when you’re on a diet.
Lidia Daimiel, researcher at the Madrid Institute of Advanced Studies (IMDEA food) and the Obesity and Nutrition Network Research Center (Ciberobn), insists that “the body is not equally prepared at any time of the day to manage food” . Therefore, when you eat is a determining factor in the chronobiology of an individual, she explains: “When you eat is as important as what you eat. If what you eat is good and healthy, but the timing is not right, you are not getting the benefit that that food could bring you in the same magnitude.”
Quality sleep and fasting
In practice, the impact on health can be global. “Once the time is set, it can affect everything,” summarizes Garaulet. An editorial in Frontiers of Nutrition compiled, a few months ago, that chronodisruptive eating behaviors “have been implicated in many health disorders, including sleep disorders, cardiometabolic risk, unbalanced mobilization of energy, dysregulation of body temperature, weight gain and psychosocial discomfort,” among others. .
Another scientific review recalled in 2020 that “experimental and clinical studies have consistently shown that alteration of circadian rhythms can favor the development and progression of digestive pathologies, such as irritable bowel syndrome and inflammatory bowel diseases.” Likewise, research on mice published in 2023 in the journal Science pointed out that synchronizing feeding with the circadian clock mitigates obesity: animals that ate in active phases of their circadian cycle burned more calories and reduced the risk of developing this ailment.
Disruption in natural meal times also impacts sleep. “Sleep is an external synchronizer, like mealtime, and it sets your clocks; But, at the same time, it is also a consequence of your internal clock and there may be alterations, such as eating late, which can alter sleep because you cannot digest properly,” Garaulet adds.
In the context of chrononutrition, the figure of fasting and its influence on modulating internal clocks also makes its way. “Time-restricted intake, which means that the number of hours of eating is reduced, is being studied. What we know is that when fasting is done early, it works better than if we move it to the afternoon and delay breakfast,” explains Daimiel. The scientist defends that fasting helps to “reset” the body and “helps launch epigenetic mechanisms that help control nutrient metabolism.”
But there are many doubts to be resolved, he clarifies, and the scientific community is not clear, for example, “if fasting is better [limitar el tiempo de ingesta] that calorie restriction [reducir el número de calorías que se ingieren]”. Furthermore, he adds, as there are many different fasting protocols, “it is not known which is the best because it is unknown how each one influences circadian rhythms.”
No magic recipes
Scientists warn that there are no magic recipes or infallible recommendations about the appropriate time to eat. Garaulet assures that there are more than 300 identified genes that define the predisposition of each individual to be more morning or evening: “There are people who, if they have dinner at 12 at night, since their biological night begins at 1 in the morning, Well, it doesn’t affect him. Each individual has different biological nights and the time at which he eats will affect him depending on his internal chronotype.” For this reason, Daimiel emphasizes that “it is very difficult to give global advice. But there are two general messages: do not eat late and do not have dinner too close to bedtime,” Daimiel says.
Chrononutrition, however, is an expanding science and there are still issues to be resolved. For example, Garaulet points out: “It is not clear nor are there studies that confirm that changing the hours of intake improves the prognosis of obesity.” Daimiel, for his part, points out another key mystery to be resolved: “There is a lot of knowledge about how the circadian rhythm is controlled, but the difficulty now is learning to modulate this to our metabolic convenience. The work is to see how, through nutrition, the clocks align: what dietary protocols can be applied to set our clocks.”