New research suggests there may be an ideal time window for eating during the day.
Eating relatively early may be beneficial for weight loss, and keeping meals within 10 hours could improve blood sugar and cholesterol levels, according to two small studies published Tuesday in the journal Cell Metabolism.
The first study found that eating later made people hungrier over a 24-hour period than when they ate the same meals earlier in the day. Late meals also caused study participants to burn calories at a slower rate, and their fat tissue appeared to store more calories during a later meal schedule than when they started. Overall, the study suggests that eating later may increase a person’s risk of obesity.
The second study, in a group of firefighters, found that eating meals within a 10-hour window reduced “bad cholesterol” particles, suggesting a potential reduction in heart disease risk factors. This dietary window also improved blood pressure and blood sugar levels in firefighters with underlying health conditions such as diabetes, high blood pressure and high cholesterol.
Both studies add to existing evidence that there may be optimal times to start and stop eating, according to Courtney Peterson, an associate professor of nutritional sciences at the University of Alabama at Birmingham who has no participated in neither study.
“You have this internal biological clock that allows you to do different things better at different times of the day. It seems like the best time for your metabolism for most people is mid or late morning,” Peterson said. .
Previous research has shown that circadian rhythms — the body’s internal clock that helps regulate sleep and waking — can influence people’s appetite, metabolism, and blood sugar levels.
Satchidananda Panda, co-author of the firefighter study and professor at the Salk Institute, said a 10-hour window seems like a “sweet spot” because the more severe restriction that characterizes many intermittent fasting diets is difficult to maintain.
“When we think about six or eight hours, you can see a benefit, but people might not stick with it for a long time,” Panda said.
Eating late might’tip the scales towards weight gain
The first of two new studies involved 16 overweight or obese people. They tried two different diets for one day each. First, some of the participants started eating an hour after their natural waking time, while the others waited to start eating until about five hours after waking up. Then the two groups changed their schedules to a later date.
The meals they all ate were identical, and the amount of calories and nutrients was consistent across both programs, according to Frank Scheer, lead author of the study and director of the medical chronobiology program at Brigham and Women’s Hospital.
The researchers measured the participants’ hormone levels and found that eating late reduced levels of leptin – a hormone that helps people feel full – by an average of 16%. Eating late also doubled the chances of people feeling hungry (people self-reported their appetite levels 18 times throughout the day).
Additionally, the researchers found that late eaters had an increased desire for starchy and savory foods, as well as meat, dairy, and vegetables. Scheer said this could be because people crave more energy-dense foods when they’re hungrier.
The study also found consistent changes in fatty tissue associated with the late diet, suggesting an increased likelihood of new fat cells forming and a decreased chance of burning fat.
Finally, the results showed that the late eaters burned about 60 fewer calories than the early eaters per day, although Peterson said this was equivalent to “eating half an apple more per day, so it’s not a such a big change.”
Although a study published last month in the same journal found that people didn’t burn more calories eating a large breakfast and a light dinner, Peterson said the two studies measured a different set of outcomes.
“Your body processes calories differently when you eat late in the day. That tips the scales in favor of weight gain and fat gain,” Peterson said, adding, “Based on this study, we can get pretty clear recommendations that people shouldn’t skip breakfast.”
But Scheer said more research is needed before recommendations can be made.
10-hour food window may reduce risk factors for heart disease
In the second study, 137 firefighters in San Diego, California, followed a Mediterranean diet rich in fruits, vegetables, fish and olive oil for 12 weeks. Seventy firefighters ate their meals within a 10 a.m. window, while the rest generally ate over 1 p.m.
Firefighters logged their meals in an app and wore wearable devices to help researchers track their blood sugar levels. Most of the participants in the 10-hour group ate between 8 or 9 a.m. and 6 or 7 p.m. (although they sometimes wandered out the window, spanning an 11 or 12-hour period).
In healthy firefighters, the time-restricted diet showed “beneficial effects that should result in less plaque buildup in the arteries and less cardiovascular disease,” Peterson said. Firefighters in this group also reported improved quality of life.
In firefighters with pre-existing risk factors for heart disease, time-restricted feeding decreased blood pressure and blood sugar.
“There has been a lot of evidence that time-restricted eating improves blood sugar control and blood pressure, but this is the first study to really test this on a large scale in people who work shifts” , Peterson said.
Panda said previous animal research has shown that during periods of fasting, “organs rest from digesting food so they can divert their energy to cell repair.”
A period of fasting also appears to allow accumulated toxins to break down, Panda said. And Peterson added that during fasts the body can get rid of sodium, which lowers blood pressure.
She said she wouldn’t be surprised if we eventually see national recommendations on eating windows or meal times over the next five to 10 years in the United States.