Breakfast at 7 a.m. during the workweek might turn into brunch at 10 a.m. on Saturday. Dinner might shift by a couple of hours, too. A new study suggests those routine weekend changes could be worth paying attention to, although the findings are not a reason to put every meal on a strict schedule.
Researchers followed more than 104,000 French adults and compared when they typically started and stopped eating on weekdays and weekends. Among men, larger shifts in that daily eating window were associated with a higher risk of cardiovascular disease, particularly coronary heart disease. No significant link was found among women. But this was an observational study, so it cannot show that inconsistent meal times caused the difference.
The study, published in Communications Medicine, used data from the long-running NutriNet-Santé study in France. Participants completed repeated 24-hour food records that included both what they ate and when they ate it.
Researchers used those records to compare the midpoint of each person's daily eating period on weekdays and weekends. They called the difference “eating jetlag.”
Most participants, 71%, kept their weekend eating schedule within an hour of their weekday schedule. About 24% shifted later by more than an hour, while about 5% shifted earlier by more than an hour.
Over a median follow-up of 8.1 years, researchers documented 2,368 cardiovascular events.
Among men, each additional hour of difference between weekday and weekend eating schedules was associated with a 14% higher relative risk of cardiovascular disease and a 21% higher relative risk of coronary heart disease. The pattern was still there even after researchers took diet quality, exercise, smoking, alcohol use, body weight, calorie intake and usual meal timing into account.
Those percentages describe relative risk, not an increase of 14 or 21 percentage points in an individual's chance of developing heart disease.
The researchers also looked at whether different weekday and weekend sleep schedules could explain the result. They did not appear to. Among men with available sleep data, the association remained after researchers accounted for bedtime and sleep duration.
It also did not seem to matter whether weekend meals shifted earlier or later.
Among men, moving the eating window more than an hour earlier on weekends was associated with a higher risk of both cardiovascular disease and coronary heart disease compared with keeping a fairly consistent schedule. Moving it more than an hour later was associated with a higher risk of coronary heart disease.
That makes this study different from research focused mainly on whether people eat especially early or late. Here, the bigger question is whether regularity itself might matter.
As study author Bernard Srour put it in the news release, “maintaining consistent meal times between weekdays and weekends may be just as important” as when those meals occur.
The findings also held up after researchers accounted for participants' average first and last eating times, suggesting the pattern was not simply because one group routinely ate later than another.
Still, the study does not show that keeping breakfast and dinner at the same time every day will protect the heart.
People with regular meal schedules may differ from people with changing schedules in ways researchers cannot fully measure. Work demands, stress, nighttime light exposure, medication timing and other factors could influence both when people eat and their cardiovascular health.
The study also made a practical assumption that will not fit everyone: researchers treated Monday through Friday as workdays and Saturday and Sunday as days off. They did not have participants' actual work schedules, so that approach would miss people who work nights, weekends, rotating shifts or other nontraditional schedules.
There are also limits to how broadly the findings can be applied. About 79% of participants were women, and volunteers in NutriNet-Santé tend to be more educated and health-conscious than the French population overall. Cardiovascular disease was also less common in the study group than in France as a whole.
The apparent difference between men and women deserves caution, too. The study found the association in men but not women, but it could not prove that men and women truly respond differently.
For now, the findings add to growing evidence that nutrition may involve more than what and how much people eat. When people eat, and how consistent that schedule is, may matter too. But researchers will need to see the same pattern in other populations before regular weekend meal times can be considered a proven way to lower heart disease risk.
The NutriNet-Santé study is supported by several French public health, research and university institutions. This project also received public funding from INRAE and the French National Research Agency.