More than two years less: The daily habit linked to a shorter life expectancy

A new study published in the scientific journal "European Journal of Clinical Nutrition" raises the possibility that the time we start and finish eating during the day is linked to health and life expectancy. The researchers examined data from more than 31,000 Americans aged 40 and over and found that the later the first meal was, the higher the risk of death. However, they warn against rushing to conclude that eating at a certain time is what causes this.

Most nutrition recommendations deal with the question of what to eat: how many vegetables, how much protein, which fats, and how much sugar. The new study examined a different and much simpler question: at what time do we eat? The researchers analyzed data from 31,044 adults in the USA. Each participant reported what they ate and drank during the day and at what time. The researchers then checked what happened to the participants over the following years.

For the purpose of the study, the "first meal" was the first time a person consumed food or a drink with calories after 4:00 AM. Therefore, it is not necessarily a regular breakfast – a drink containing calories could also be counted. The researchers tracked mortality data until the end of 2019. During a median follow-up period of 8.6 years, 7,129 of the participants died, including 2,259 from heart and blood vessel-related diseases.

The researchers compared the participants to people who ate for the first time between 7:00 and 8:00 AM. Those who started eating between 8:00 and 10:00 were found to have a 10% higher risk of death from any cause. When the first meal was between 10:00 and 12:00, the gap rose to 19%. The most prominent result was found in people who ate for the first time only after 12:00 PM: they were found to have a 29% higher risk of death from any cause.

When the researchers checked deaths from heart and blood vessel diseases, the gap was even larger. Those who started eating after noon were found to be at a 46% higher risk compared to those who ate between 7:00 and 8:00. According to the calculation made in the study, at age 50, the estimated life expectancy of those who started eating after noon was on average 2.46 years shorter.

And what is the best time to stop eating? Here the picture was less simple. The researchers found that it was not only very late eating that was linked to an increased risk. People who finished eating relatively early also showed similar results. Compared to those who ate for the last time between 19:00 and 20:00, those who finished before 19:00 were found to have a 13% higher risk of death from any cause. People who ate after midnight had a 27% higher risk.

According to the calculations, the lowest risk was found around 20:00. But the researchers emphasize that this figure does not mean that everyone should finish dinner at exactly that time. "It does not mean that 19:00 to 20:00 is the best dinner time for everyone," explained senior researcher Zhilei Shan.

Why does it matter when we eat at all? One of the possibilities is related to the body's biological clock. Simply put, our body works differently at different times of the day. The internal clock affects sleep, hormones, and the way the body uses sugar and fat. The food we consume also signals to the body what stage of the day we are in.

According to Shan, eating for the first time at a late hour or consuming food during the night hours may be linked to a disruption of the internal clock and damage to the way the body processes sugar and fats. Animal studies have already found a link between eating at certain hours and weight gain, fat accumulation in the liver, and disruptions in the activity of various organs. However, it is still unclear if the same processes also explain the results found in humans.

The study does not prove that late eating causes early death. It is possible that the situation is the opposite: people who suffer from health problems may change their eating times. Shift work, irregular sleep, and economic status can also simultaneously affect meal times and health.

For example, the researchers found that people who finished eating relatively early tended to be older and suffer from more diseases. Therefore, it is possible that they ate early because of their health condition – and not that the early meal is what harmed their health. "Therefore, late eating should be treated as a possible sign of risk, and perhaps as a habit that can be changed, rather than as proof that it directly causes mortality," explained Shan.

The researchers also checked how many hours a day the participants ate – that is, how much time passed between the first and last calorie consumption. When they also took into account the time when eating started, they did not find a simple and consistent link between the number of eating hours and the risk of death among all participants. That is: it may not be enough to count how many hours one fasts. The time when one starts eating may also be important.

One of the main limitations is that the study relied mainly on the participants' reporting of what they ate during one day. A single day does not necessarily represent their habits over years. In addition, this is a study that checked links between habits and health outcomes, not an experiment where researchers determined for people when to eat and checked what happened to them. Therefore, the researchers themselves also ask not to turn the findings into a new rule. "Based on these findings alone, people should not make extreme changes to their eating times," said Shan.