A New Study Says When You Eat Might Matter More Than When You Sleep

Timing is everything. And according to a new study by scientists at Mass General Brigham, that includes when you eat your food for optimal heart health, too. 

On April 8, researchers published their findings in the journal Nature Communications, assessing whether limiting meals to daytime hours could protect heart and blood vessel health, especially for those who are awake or asleep during irregular hours — such as night shift workers, individuals with sleep disorders, or frequent travelers across time zones. 

To reach their conclusion, the team conducted a carefully controlled lab study, splitting 20 healthy volunteers into two groups: a control group that ate their meals both during the day and at night to replicate real-world shift workers and their usual eating schedules, and an intervention group that only ate during the day. The participants took part in the study for two weeks, during which they had no access to windows, electronics, or watches, ensuring their bodies had no clues about the time of day.

Part of that time was spent on a “forced desynchrony” schedule, meaning each “day” lasted 28 hours instead of the usual 24. They also went through two special “constant routine” periods, one lasting about 32 hours and the other about 40 hours, during which they stayed awake, reclined in a dimly lit room, and had hourly snacks — which does sound suspiciously like a typical workday these days.

Then, they were asked to participate in “night work.” Throughout the study, both groups maintained the same nap cycle to ensure they all had the same sleep cycle to measure against. This means the only difference between the two groups was their eating times.

“Our study controlled for every factor that you could imagine that could affect the results, so we can say that it's the food timing effect that is driving these changes in the cardiovascular risk factors,” Sarah Chellappa, MD, MPH, PhD, an associate professor at the University of Southampton, and lead author for the paper, shared in a statement. 

Throughout the study, the researchers measured several heart health and blood clotting risk factors, including heart rate variability (HRV) to evaluate how well the heart adapts to changes, the levels of plasminogen activator inhibitor-1 (PAI-1), a protein that regulates blood clotting, as well as both heart rate and cortisol levels to assess stress.

And here's where it gets interesting: The researchers observed lower HRV and higher PAI-1 only in the group that ate day and night, suggesting an increased risk of blood clotting for those who eat around the clock.

Meanwhile, the intervention group (the daytime-only eaters) experienced no negative changes in HRV or PAI-1. In fact, this group demonstrated a 6–8% reduction in blood pressure. The authors noted that this suggests when we eat our meals may be more important for heart health than when we sleep. The study's findings also indicate that for those who work night shifts or often face sleep disruptions, restricting meals to daytime might help mitigate some of the heart risks associated with these irregular schedules.

“Our prior research has shown that circadian misalignment — the mistiming of our behavioral cycle relative to our internal body clock — increases cardiovascular risk factors,” said senior author Frank A.J.L. Scheer, PhD, a professor of medicine and director of the Medical Chronobiology Program at Brigham and Women's Hospital, a founding member of the Mass General Brigham healthcare system. “We wanted to understand what can be done to lower this risk, and our new research suggests food timing could be that target.”