Timing Meals Correctly Could Redeem a Crappy Diet

A new study reveals the best hours to eat.

Lady's hand with red nails holding a hamburger
(Image credit: Getty Images)

There may be a way to lose weight without changing what you eat: Change when you eat it.

While restricting eating hours (i.e., eating in a small window of time by eating breakfast later and finishing dinner earlier) may not be convenient or ideal for people who get up early and go to sleep late, new research suggests that eating within a nine- to 12-hour daily window could prevent obesity and even cure it — even if your diet's not so healthy, or if you sometimes cheat and eat outside your designated times.

In a 38-week study recently published in the journal Cell Metabolism, scientists fed mice four different diets with the same number of calories but different components: One diet was loaded with fat, another high in fructose, one was high in fat and sucrose, and one consisted of regular mouse food. The researchers let some mice in every diet group eat whenever they wanted, while other mice were only allowed to eat during nine-, 12-, or 15-hour windows. Some lucky guys got cheat days on the weekends, while some less-lucky mice on the eat-whenever-you-want feeding schedule were switched to time-restricted diets halfway through the study.

At the end of the 38 weeks, mice who ate at all hours gained weight, which can lead to some serious health issues. Even though all the mice on time-restrictive diets ate the same amount of calories as the mice who ate whenever, those who ate during nine- or 12-hour windows (and those who sometimes ate outside their designated hours) emerged from the study without weight gain and less body fat than mice that ate the same kind of diet over the course of 24 hours. What's more interesting: The mice that switched diets during the study even lost some of the weight they'd gained. Their actual diets didn't seem to matter as much as when they ate. 

Researchers don't know exactly why the body reacts differently to food at different times. One of their theories is that meal timing affects your circadian rhythm, which could either stoke or slow your metabolism.

Either way, the implications of this study are pretty clear (and study authors suggest the findings could ring true in humans too): Limiting your eating hours could help the body fend off weight gain. Of course, there's no reason to fix something that's not broken. If your eating schedule works for you (and your school/job/social life/appetite schedule), and you're in perfectly good health, eat whenever your appetite compels you. Late-night pizza, anyone?

Still, this new science isn't license to trade your salad lunch for the caloric equivalent of dessert, eaten at noon. (Some calories — ahem, those found in fruits and veggies — contain more vitamins and minerals, and provide more sustainable energy than anything you'll find in cake.)

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Elizabeth Narins

Elizabeth Narins is a Brooklyn, NY-based writer and a former senior editor at Cosmopolitan.com, where she wrote about fitness, health, and more. Follow her at @ejnarins.