Scientists have linked changing meal times with the risk of heart disease

The difference in meal times between workdays and weekends may be associated with an increased risk of cardiovascular disease in men. Each additional hour of this shift corresponded to a 14% increase in relative risk and a 21% increase in the risk of coronary heart disease. What is a food jetlag, why it can disrupt the internal rhythms of the body and whether this means that a late breakfast on Saturday is dangerous to health — in the Izvestia article.

What is a food jetlag?

A food jet lag is a discrepancy between the time of meals on working and free days. On weekdays, the schedule is usually determined by work or study, whereas on weekends a person can wake up later, have breakfast and dinner.

To assess the shift, researchers determine the middle of the daily feeding window. For example, if a person eats from 08:00 to 20:00 on weekdays, the middle of this period falls at 14:00. If on weekends the first meal takes place at 10:00 and the last one at 22:00, the middle is shifted to 16:00. In this case, the food jet lag is two hours.

A similar concept is used in the study of sleep. A social jet lag occurs when the sleep and wake-up schedule on weekdays does not match the schedule on weekends. In both cases, the body is forced to switch between different time modes regularly, although the person does not cross time zones.

For the first time, the authors of the new work studied the relationship of food jet lag not only with intermediate indicators — body weight, blood pressure or sugar levels — but also with a long-term risk of developing cardiovascular diseases.

How the research was conducted

The study involved experts from INRAE, Inserm, Sorbonne-Paris-Nord University, Paris-Cité University and the National Conservatory of Arts and Crafts. The researchers analyzed data from 104,806 adult participants in the French NutriNet-Santé project, collected from 2009 to 2023. The average age of the volunteers when included in the study was 42.7 years, about 79% of the sample were women.

The participants filled out detailed daily nutrition diaries. They recorded foods and drinks, the time of their consumption and the availability of calories. On average, each person provided 5.8 records covering both working and free days.

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Based on the time of the first and last high-calorie meal, the researchers calculated the middle of the weekday and weekend meal window. The difference between these values was used to assess the severity of food jetlag.

The participants were also divided into three groups. In the first group, the meal window on free days started on average two hours earlier than on working days. In the second, the schedule practically did not change. In the third group, weekend meals were shifted to a later time by an average of one hour and 40 minutes.

The median follow—up period was 8.1 years, and the total duration was more than 814,000 person-years. During this time, the researchers registered 2,368 new cases of cardiovascular diseases, including 1,270 cases of coronary heart disease and 1,098 cerebral circulatory disorders. The participants' reports of diagnoses were checked against medical records.

How the schedule change turned out to be related to the heart

Among men, each additional hour of jet lag corresponded to an increase in the relative risk of cardiovascular disease by an average of 14%. For coronary heart disease, the rate reached 21%.

The relationship was observed regardless of the direction of the shift. A higher risk was found both among men who started eating earlier on weekends and among those who postponed the meal window to a later time. The participants with a stable schedule had the most favorable indicators.

In the calculations, the authors took into account age, education, profession, marital status, number of children, smoking, alcohol consumption, physical activity, diet quality and sleep duration. After statistical corrections, the association between food jetlag and diseases in men persisted.

At the same time, the indicator of 14% does not mean that a single change in breakfast time increases the individual probability of illness by 14 percentage points. We are talking about the relative difference in risk between participants in a statistical model calculated on the basis of long-term observations.

The results also cannot be transferred to a separate weekend. The study evaluates the habitual, regularly recurring gap between routines, rather than the effects of a single brunch, holiday dinner, or vacation schedule change.

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Why wasn't the connection found in women

There was no statistically significant association between dietary jetlag and cardiovascular diseases among women. This does not prove that changing the regime is completely safe for them. The authors consider several possible explanations. The first is related to gender differences in the work of the biological clock and the metabolic response to circadian rhythm disorders. Data from animal experiments show that male and female organisms can react differently to such changes.

The second explanation concerns lifestyle and professional workload. Work schedules, the frequency of night shifts, family responsibilities, and other social factors can affect men's and women's sleep patterns and diets in different ways. Finally, the absolute risk of cardiovascular diseases in men is higher on average, especially in the younger and middle age groups. Therefore, during the same observation period, more events could have accumulated among them, which are necessary to identify a statistical relationship.

The result obtained looks especially remarkable against the background of the earlier work of the same research group. In 2023, an analysis of NutriNet-Santé data showed that late first and last meal times were associated with cardiovascular risk mainly in women. However, the two jobs measured different characteristics: the first one was a specific meal time, and the new one was the stability of the schedule between working and free days. It cannot be concluded that for men, only regularity matters, and for women, only the time of meals. Rather, the results show that sex differences need to be studied separately in more balanced samples.

How is food intake related to the biological clock?

The body's main biological clock is located in the suprachiasmatic nucleus of the brain and is primarily synchronized with the cycle of light and dark. At the same time, their own rhythms exist in the liver, pancreas, adipose tissue, heart and blood vessels. Meal time serves as an important signal for these peripheral clocks. It helps the body prepare in advance for the intake of nutrients, change the secretion of insulin, the digestive system and the use of glucose and fats.

If sleep continues to follow the same schedule, and nutrition constantly moves between different time windows, individual body systems may receive conflicting signals. The authors suggest that such internal desynchronization can affect glucose control, lipid metabolism, blood pressure, inflammatory processes, and hormonal regulation.

However, these mechanisms remain a likely explanation rather than a proven result of the new work. The study did not directly measure the state of the biological clock in tissues and does not show which process could lead to the development of diseases.

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Previous data supports the general hypothesis about the role of meal schedules. In 2023, a study of more than 103 thousand NutriNet-Santé participants, published in Nature Communications, showed the association of late first and last meals with cardiovascular diseases. The differences between the participants who started eating after 09:00 and before 08:00, as well as those who finished eating after 21:00 and before 20:00, were especially noticeable.

A small American study in 2021 also linked a fickle meal schedule to less favorable indicators of body weight, waist circumference, blood pressure, and glycated hemoglobin. However, only 115 women participated in the study, so its results cannot be directly compared with data from a large French cohort.

Is brunch harmful?

The main limitation of the work lies in its observational nature. The scientists did not randomly assign different eating patterns to the participants, but rather analyzed habits that already existed in their lives. Therefore, the discovered relationship does not allow us to prove that it was the change in meal time that caused the diseases.

Food jetlag may accompany other lifestyle features. People with irregular work schedules are more likely to face night shifts, stress, and lack of sleep. On weekends, late meals can be combined with alcohol consumption, a less balanced diet, or reduced physical activity.

The statistical model took into account many of these factors, but it is impossible to completely exclude the residual influence. The researchers did not have detailed information about work stress, exposure to light at night, the use of certain substances, the time of medication and physical activity during the day.

Sleep data was obtained from only a part of the participants and was collected separately. In addition, the diet was assessed based on several daily diaries at the beginning of the follow-up. Over the following years, a person's habits may have changed. The sample was also not representative of the entire French population. The participants of NutriNet-Santé voluntarily registered in an online nutrition project and could be more interested in health than the general population. The predominance of women further limits the accuracy of conclusions about the male part of the group.

Do I have to eat strictly by the hour now

The study does not establish a safe interval and does not require eating every minute according to the same schedule. It also does not allow you to prescribe a regular meal schedule as an independent way to prevent cardiovascular diseases.

The practical conclusion so far is that the stability of the schedule deserves further study along with the composition of the diet, the amount of food and the time of dinner. This issue may be especially relevant for people who work at night or on a shift schedule, since their sleep and nutrition patterns are disrupted at the same time.

Randomized trials will be required to move from a statistical relationship to medical recommendations. In them, participants will need to set a more stable or changing schedule for a long time and monitor blood pressure, glucose levels, inflammatory parameters and other risk factors.

In the meantime, the regularity of meals can be considered as a possible additional component of a healthy regime, but not as a substitute for proven preventive measures. These include quitting smoking, physical activity, blood pressure and cholesterol control, adequate sleep, and a balanced diet.