What’s more, people are now eating at times of the day when historically they would have been asleep, says Satchin Panda, a circadian biologist at the Salk Institute for Biological Studies in La Jolla, Calif., who co-wrote an overview on the timing of eating in the 2019 Annual Review of Nutrition. For thousands of years, he says, our nightly fast probably started much earlier than in these times of late-night television.
Although the research is still mixed, the timing of eating seems to matter for body weight and health. Studies suggest significant potential benefits from fasting every other day or so — or, on a daily basis, eating only when we would normally be awake, within a window of 12 hours or fewer — a practice known as time-restricted eating.
Still, some researchers think the problem with such disappointments might lie in timing. Peterson suspects that in both these studies, the last daily meal might have been consumed too late, when blood insulin levels had dropped too low to process food properly.
In 2018, Peterson and her colleagues reported lower blood pressure and better-controlled blood sugar levels in eight overweight prediabetic men asked to eat all their food within a six-hour window — but with dinner before 3 p.m. If confirmed with more people, the study would indicate that restricting eating to a window of less than 12 hours while we are awake can have health benefits independent of calorie reduction, as long as the window isn’t too late in the day.
And what’s going on in the body to make it healthier to eat at one time than another? Daily biological rhythms may be central here, says Dorothy Sears, an obesity researcher at Arizona State University. It’s during the day that your body is best able to process food, says Sears, who wrote about the metabolic effects of intermittent fasting in the 2017 Annual Review of Nutrition. And just as the brain needs rest at night to do much-needed repair and cleanup work, so does the body, Panda says.
All the unsettled points and lack of clear-cut evidence from human trials hasn’t stopped thousands of enthusiasts from experimenting with their own personal intermittent-fasting regimens, in large part because many find it easier to count hours than calories. And there’s hope it might become easier still, if what goes for mice goes for people: Panda’s rodent studies suggest that skipping weekends doesn’t ruin the time-restricted health effect.
“You think, ‘What about Saturday night, when I go out for a late dinner?’ In the mice, that is okay,” Sears says. “It’s very encouraging, because it seems that you don’t have to ask people to be perfect every day of the week. . . . And you don’t ever have to read a label.”
