Chrononutrition: ‘When you eat is as important as what you eat’

A mismatch between the time of meals and the human body’s biological clock increases the risk of diseases because many organs function on a schedule

Eating late can influence your ability to lose weight.SrdjanPav (Getty Images)
Jessica Mouzo

The way you eat is essential for your health. But not only do what and how much we eat have an influence, but also when we eat. In recent years, science has focused on unraveling the phenomenon of chrononutrition, which explains the relationship between time-related eating patterns, circadian rhythm, and metabolic health. And research has already shed light on the importance of food intake times that are synchronized with our circadian rhythm, which is the 24-hour biological clock that regulates internal physiological functions. For example, scientists have discovered that skipping breakfast is associated with a higher risk of obesity, and eating late dinners is also linked to weight gain.

Humans have a kind of central clock that sets the time for the body. At first glance, it is a barely one-millimeter ball located in the hypothalamus, but these tiny molecular devices are capable of telling the time to the rest of the body. Together with the small chronometers that are independent of the tissues, they anticipate and prepare the cells for 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 world, mainly through light and darkness, but also with changes between eating and fasting or with periods of activity and rest,” Marta Garaulet, a professor of Physiology at the University of Murcia and expert in chrononutrition explains.

Keeping to our circadian rhythm and all the 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.”

Internal biorhythms are regulated through the central clock, peripheral chronometers (which are in organs and tissues), lifestyle habits, behaviors, and the environment. “A person who is in good chronobiological health is one who has all their clocks synchronized in accordance with the changes of light and darkness,” Garaulet says. 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, “are related to diseases, such as obesity, cancer, depression, or metabolic alterations,” says the scientist. “This is clearly seen in shift workers or employees who work at night, people whose behaviors are misaligned with their internal clock.”

Mealtimes as a synchronizer

Mealtimes, like light, are a clear modulator of internal clocks, says Garaulet. “Mealtimes synchronize the peripheral clocks of food-related organs such as the liver and pancreas. If you eat at the wrong time, none of the organs that prepare to receive the food react well. This is because receiving food has a large impact on the body and it has to prepare for it,” says the specialist, who goes into more detail about this explanation: “It is as if 100 people have come to eat at your house and they didn’t tell you in advance. The 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 certain way, and the organs function accordingly. That is, in a different way during the 24 hours of the day: they do not respond in the same way 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 and the Obesity and Nutrition Network Research Center, insists that “the body is not equally prepared to manage food at just any time of the day.” For this reason, 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 at the same magnitude that that food could give you.”

Quality sleep and fasting

In practice, there can be an impact on overall health. “Once the time is set, it can affect everything,” says Garaulet. A few months ago, an editorial in Frontiers of Nutrition brought together studies indicating that chronodisruptive eating behaviors “have been implicated in many health disorders, including sleep disorders, cardiometabolic risk, unbalanced energy distribution, deregulation of body temperature, weight gain, and psychosocial discomfort,” among others.

In 2020 another scientific review recalled that “experimental and clinical studies have consistently shown that alteration of circadian rhythm 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 indicated 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 disease.

Disruption in natural mealtimes also impacts sleep. “Sleep is an external synchronizer, like mealtimes, 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, fasting and its influence on modulating internal clocks also has an impact. “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 questions to be resolved, she says, and the scientific community is not clear. For example, “whether fasting [limiting the time of intake] is better than caloric restriction [reducing the number of calories ingested].” Furthermore, she adds, as there are many different fasting protocols, “we don’t know which is the best because we don’t know how each one influences circadian rhythms.”

No magic formula

Scientists warn that there are no magic formulas or infallible recommendations for the appropriate time to eat. Garaulet says that there are more than 300 identified genes that define the predisposition of each individual to be more of a morning or evening person: “There are people who, if they have dinner at 12 at night, are not affected, since their biological night begins at 1 in the morning. Each individual has different biological nights and the time at which they eat will affect them depending on their internal chronotype.” For this reason, Daimiel emphasizes that “it is very difficult to give overall 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 for 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 the clocks align through nutrition: what dietary protocols can be applied to set our clocks.”

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