Eating for the first time between 7 and 8 a.m. and having your last meal between 7 and 8 p.m. were associated with the lowest mortality risk in a study that followed more than 31,000 U.S. adults. By moving the first meal further and further forward, the association grew: +10% between 8 and 10, +19% between 10 and midday, up to +29% after 12. For those who ate after midnight, the associated increase reached 27%.
The research, published onEuropean Journal of Clinical Nutritiontherefore brings the clock into a field of nutrition that looks less and less only at what we put on our plates. Even when we eat it could have an impact, especially when the first and last meal end very far from the central hours of the day.
The later the first meal arrived, the more the associated risk increased
Wen Hu and colleagues at Huazhong University of Science and Technology in Wuhan analyzed data from 31,044 people aged 40 or older participating in the US National Health and Nutrition Examination Survey between 1999 and 2018.
During a median follow-up of 8.6 years, 7,129 deaths were recorded. The authors then compared the times of the first and last meals with all-cause and cardiovascular mortality.
The 7-8 am time slot was used as a reference for the first meal. Among those who ate from 8 to 10 the hazard ratio was 1.10, between 10 and 12 it rose to 1.19 and after midday it reached 1.29. In more immediate terms, compared to the 7-8am group it corresponds to an associated increase of 10%, 19% and 29% respectively.
The progression is rather regular: the further the first meal was from the morning, the more the observed association with mortality grew.
The work technically speaks of the first meal of the day, so that data can include both a very late breakfast and people who had skipped breakfast completely. The times were obtained from a food questionnaire covering the previous 24 hours, one of the limits to keep in mind when transforming highly variable daily habits into numbers to follow for years.
A U-shaped curve appears for dinner
With the last meal the matter becomes more curious. The range associated with the lowest risk was between 7pm and 8pm, used by the authors as a reference.
Those who had last eaten before 7pm showed a 13% higher all-cause mortality rate. At the other extreme, after midnight, the associated increase reached 27%. The associations also appeared when analyzing cardiovascular mortality separately.
So simply anticipating dinner as much as possible is not what these data suggest. The trend looks more like a U-shaped curve, with less favorable results at the two ends and a central band around 7-8pm.
The authors also studied the duration of the so-called eating windowi.e. the number of hours between the first and last meal. For cardiovascular risk, the ratio also changed depending on the time in which that window began: another indication that, at least according to this analysis, where we place meals during the day also matters, in addition to the simple duration of fasting.
More than two years difference in estimated life expectancy
The researchers also tried to transform these associations into a more intuitive measure, estimating life expectancy starting from age 50.
Among people who ate their first meal after midday, estimated life expectancy was on average 2.46 years shorter than in the 7-8 am group. For those who ate their last meal after midnight, the difference was 2.35 years compared to the 19-20 age group.
These are estimates built on cohort data, so not a personal countdown to apply to last night’s dinner. Rather, they serve to make visible the extent of the association observed across a large population.
What do circadian rhythms have to do with it?
One of the explanations called into question comes from circadian rhythms, the internal clock that coordinates sleep, hormone secretion, body temperature and metabolism during the 24 hours.
In fact, the body does not manage nutrients and glucose in exactly the same way at eight in the morning and at midnight. Eating very late can coincide with a biological phase less favorable to the management of sugars and fats and also interfere with sleep. It is one of the mechanisms that research on chrononutrition has been studying for years.
This work remains observational: the authors identified associations, without assigning people to different times to demonstrate a direct cause-effect relationship. Age, health conditions, lifestyle and other characteristics were considered in the analysis, but in studies of this type not all differences between early eaters and very late eaters can be eliminated.
The central fact, however, remains rather simple. In the population studied, the first meal between 7 and 8 am and the last between 7 and 8 pm coincided with the most favorable trends, while very late times were associated with higher mortality. The hands, it seems, could deserve a place next to the menu.
