While breakfast advice typically emphasizes the nutritional content of meals, a significant study involving U.S. adults suggests the timing of meals may also be crucial. The study highlights a potential link between the timing of the first and last caloric intake of the day and longevity.
The research indicates an association but does not prove that altering meal times can change life expectancy. However, it supports the notion that health might be influenced not just by what we eat, but also by when we eat.
Previous studies have connected skipping breakfast and eating late at night with adverse health outcomes, though the impact of specific timings was not clearly understood.
To investigate further, researchers examined data from 31,044 adults aged 40 and above, collected through the US National Health and Nutrition Examination Survey from 1999 to 2018.
Participants provided a detailed account of everything they consumed over a 24-hour period, including the timing of each item.
The study, as published in the European Journal of Clinical Nutrition, defined any calorie-containing intake after 4 am as the “first meal,” not necessarily a traditional breakfast. The last intake of calories marked the “last meal,” and the duration between these defined the eating window.
Records were then linked to mortality data registered through the end of 2019.
Over a median follow-up of 8.6 years, 7,129 participants died, including 2,259 due to cardiovascular issues.
Factors like age, smoking, exercise, diet quality, body mass index, energy intake, income, and pre-existing conditions were considered in the analysis.
A pattern emerged relating to the timing of the first meal. Eating between 8 and 10 am, compared to 7 and 8 am, was linked with a 10 percent greater risk of death from any cause. This risk increased to 19 percent between 10 am and noon, and 29 percent after noon.
Similar patterns were observed for cardiovascular-related mortality.
Having the first meal post-noon was associated with a 46 percent higher risk of cardiovascular death compared to eating between 7 and 8 am. At 50 years of age, the later-eating group had an average life expectancy 2.46 years shorter.
The timing of the last meal showed unexpected results.
Instead of a linear increase in risk with later eating hours, the relationship formed a U-shape. Finishing the last meal between 7 and 8 pm was optimal, with risks increasing by 13 percent if eaten before 7 pm, and by 27 percent if eaten after midnight. The lowest risk was identified around 8 pm.
“However, this does not mean that 7-8 pm is a universally optimal dinner time for everyone,” senior author Zhilei Shan, from Huazhong University of Science and Technology, commented to ScienceAlert.
Shan explained that eating very late might interfere with circadian rhythms and metabolism. Conversely, an early last meal might indicate certain lifestyle patterns, illnesses, or lower energy consumption.
Early eaters tended to be older, eat less frequently, and have existing health issues, suggesting the timing might reflect their health status rather than influence it.
The eating window posed additional complexity.
When considering the timing of the first meal, the length of the eating window did not consistently correlate with mortality across the sample, but varied depending on when eating started.
This finding complicates concerns about short eating windows, indicating that focusing solely on fasting hours might overlook important aspects.
“Meal timing is an important cue for peripheral circadian rhythms,” Shan stated. “A later first meal or late-night eating may contribute to circadian misalignment and metabolic disturbances, including impaired lipid and glucose metabolism.”
Animal studies suggest possible pathways involving weight gain, liver fat accumulation, disrupted organ clocks, and altered fat absorption. However, whether these mechanisms explain mortality trends in humans is still unknown.
Reverse causation could also be possible, where late eating might result from or indicate poor health, inadequate sleep, shift work, or socioeconomic factors. Another study found breakfast tended to occur later as health problems increased among older adults.
“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 commented.
Related: Men And Women May Need Different Breakfasts For Weight Loss
The study’s primary limitations arise from its observational nature. Meal timing was mainly gathered through a single 24-hour recall, which may not accurately reflect long-term eating habits.
Chronotype, specific sleep patterns, activity timing, and other unmeasured factors could still influence the findings despite comprehensive adjustments and sensitivity tests.
“Based on these findings alone, people should not make extreme changes to their eating schedules,” Shan advised.
The study was published in the European Journal of Clinical Nutrition.
This article was fact-checked by Fiona MacDonald and edited by Fiona MacDonald. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
