Study Links Meal Timing to Longer Life

Most advice about breakfast concentrates on what belongs on your plate. Yet a large study of US adults indicates that the clock could matter as well: when you take in your first and final calories each day may be associated with longevity.

The results identify an association, rather than demonstrating that altering meal times changes anyone's destiny. Even so, they add to growing evidence that health may be shaped not just by what we eat, but also by when we eat it.

Previous research has associated missing breakfast and eating late at night with worse health, although the risks tied to particular meal times had remained uncertain.

How the meal-timing study was conducted

To investigate, researchers examined data from 31,044 US adults aged 40 and over who took part in the National Health and Nutrition Examination Survey from 1999 to 2018.

Participants detailed all food and drink they had consumed over the preceding 24 hours, along with the time each item was consumed.

In the study, published in the European Journal of Clinical Nutrition, any food or drink containing calories consumed after 4 am was treated as the "first meal". This did not necessarily mean a traditional sit-down breakfast.

The final intake of calories for the day was defined as the last meal, while the interval between the two was defined as the eating window.

The researchers connected these dietary records with deaths recorded up to the end of 2019.

Over a median follow-up period of 8.6 years, 7,129 participants died, of whom 2,259 died from cardiovascular causes.

The analysis adjusted for a range of factors, including age, smoking, physical activity, diet quality, body mass index, energy intake, income and pre-existing illness.

Later first meals and mortality risk

A trend appeared as the timing of the first meal became later.

Relative to eating between 7 and 8 am, having a first meal from 8 to 10 am was linked with a 10 percent greater risk of death from any cause. This rose to 19 percent for first meals eaten between 10 am and noon, and to 29 percent for those eaten after noon.

Deaths from cardiovascular causes showed a comparable pattern.

Eating for the first time after noon was linked with a 46 percent higher risk of cardiovascular death than eating between 7 and 8 am. On average, the group eating later also had an estimated life expectancy 2.46 years shorter at age 50.

The timing of the final meal of the day brought a less expected finding.

Instead of the risk simply increasing with each later hour, the association formed a U-shape. Compared with finishing a meal between 7 and 8 pm, eating before 7 pm was associated with a 13 percent higher all-cause mortality risk, whereas eating after midnight was associated with a 27 percent higher risk. The modelled risk was lowest at roughly 8 pm.

"However, this does not mean that 7-8 pm is a universally optimal dinner time for everyone," senior author Zhilei Shan, of Huazhong University of Science and Technology, told ScienceAlert.

Members of Dr Shan's research group at the School of Public Health, Huazhong University of Science and Technology. (Photo courtesy of Dr Shan's research group, School of Public Health, Huazhong University of Science and Technology. Used with permission.)

Shan explained that eating very late may disturb metabolism and circadian rhythms. However, having the last meal very early might reflect work schedules, illness or lower energy intake.

Those who ate early were generally older, ate less frequently and had more pre-existing illness. Therefore, the time on the clock may be signalling something about their health, rather than causing it.

Eating windows, circadian rhythms and health

The eating window introduced a further complexity.

After accounting for the timing of the first meal, the duration of the eating window had no consistent association with mortality across the full sample. Rather, its relationship varied depending on when people started eating.

This adds nuance to worries about very short eating windows: simply tallying fasting hours may overlook part of the picture.

"Meal timing is an important cue for peripheral circadian rhythms," Shan said. "A later first meal or late-night eating may contribute to circadian misalignment and metabolic disturbances, including impaired lipid and glucose metabolism."

Studies in animals suggest possible mechanisms involving weight gain, fat build-up in the liver, disrupted clocks in organs outside the brain, and changed fat absorption. It is still unknown whether these mechanisms account for mortality patterns in humans.

Reverse causation may also be involved. Late eating could result from, or act as a marker of, poor health, poor sleep, shift work or socioeconomic circumstances. Earlier research in older adults likewise found that breakfast moved later as health problems built up.

"Therefore, later eating should be interpreted as a potential risk marker, and possibly a modifiable behavior, rather than definitive evidence of a direct causal effect," Shan said.

Related: Men And Women May Need Different Breakfasts For Weight Loss

The study's main limitations arise from its observational design. Meal timing was chiefly measured using one 24-hour dietary recall at the outset, which might not reflect habitual eating over many years.

Chronotype, detailed sleep patterns, the timing of activity and other factors not measured could still have affected the findings, despite the extensive adjustments and sensitivity analyses.

"Based on these findings alone, people should not make extreme changes to their eating schedules," Shan said.

The study was published in the European Journal of Clinical Nutrition.

This article was fact-checked and edited by Fiona MacDonald. While we take pride in our process, we are only human. If you notice an error, please let us know.