Oct. 5, 2022 – New research suggests there may be better times during the day for eating and fasting.
Eating earlier in the day may help you lose weight, and eating meals within a 10-hour window could improve blood sugar and cholesterol levels, according to two new studies published in the journal Cell Metabolism.
“You have this internal biological clock that makes you better at doing different things at different times of the day,” Courtney Peterson, PhD, an associate professor of nutrition sciences at the University of Alabama at Birmingham, told NBC News. Peterson wasn’t involved with the studies.
“It seems like the best time for your metabolism, in most people, is the mid- to late morning,” she said.
In one study, researchers found that eating later in the day made people hungrier during a 24-hour period, as compared with eating the same meals earlier in the day. Late eating also burned calories at a slower rate and led to fat tissue that stored more calories. Combined, the changes may increase the risk for obesity, the study authors found.
In another study, among firefighters as shift workers, researchers found that eating meals within a 10-hour window decreased the size of bad cholesterol particles, which could reduce risk factors for heart disease. The 10-hour eating window also improved blood pressure and blood sugar levels among those with health conditions such as diabetes, high blood pressure, and high cholesterol.
The two new studies confirm findings from previous studies that indicate humans may have an ideal eating window based on the body’s circadian rhythms, which regulate sleep and wake cycles and can affect appetite, metabolism, and blood sugar levels.
In the firefighter study, for instance, the 10-hour window appears to be a “sweet spot” for the body, the authors found. More severe restrictions, as found with many intermittent fasting diets, could be difficult for the body to maintain.
“When we think about 6 or 8 hours, you might see a benefit, but people might not stick to it for a long time,” Satchidananda Panda, PhD, one of the study authors and a professor at the Salk Institute, told NBC News.
The new studies had small sample sizes, though they offer insight for future research. In the first study, 16 people who were overweight or obese tried two eating plans for 24-hour periods. Some of them began eating an hour after their natural wake-up time, and others waited to begin eating until about 5 hours after waking up. They ate the same meals with the same calories and nutrients.
The researchers measured their hormone levels and found that eating later decreased the levels of leptin, which helps people to feel full. Eating later also doubled the odds that people felt hungry throughout the day. Those in the study who ate later in the day also had more cravings for starchy or salty foods, as well as meat and dairy, which are energy-dense foods.
The research team also found changes in fat tissue, which could lead to a higher chance of building up new fat cells and a lower chance of burning fat. Late eaters burned about 60 fewer calories than early eaters during the day.
“Your body processes calories differently when you eat late in the day. It tips the scale in favor of weight gain and fat gain,” Peterson said. “From this study, we can get pretty clear recommendations that people shouldn’t skip breakfast.”
The second study followed 137 firefighters in San Diego, CA, who ate a Mediterranean diet with fish, vegetables, fruit, and olive oil for 12 weeks. Among those, 70 firefighters ate during a 10-hour window, and the rest ate during a longer window, generally about 13 hours. They logged their meals in an app and wore devices to track blood sugar levels.
In the 10-hour group, most firefighters ate between 8 a.m. or 9 a.m. and 6 p.m. or 7 p.m. The time-restricted eating appeared to be linked with health benefits, such as less harmful cholesterol buildup and reduced heart disease.
Among firefighters with risk factors for heart disease, such as high blood pressure and high blood sugar, the time-restricted eating decreased their blood pressure and blood sugar levels.
The restricted window appears to allow the body to break down toxins and get rid of sodium and other things that can drive up blood pressure and blood sugar, the authors wrote.
During periods of fasting, “organs get some rest from digesting food so they can divert their energy toward repairing cells,” Panda said.