Can You Eat Late and Still Lose Weight?

Is a calorie really a calorie, or does when you eat count too?

Lately we've heard the only thing that matters to your waistline is how much you eat. But there's a growing body of research that says when you eat really does make a difference in how much you weigh.

"Your body is more prone to burn fat at certain times of day and store fat at other times," says Satchin Panda, PhD, associate professor in the Regulatory Biology Laboratory at the Salk Institute in La Jolla, California.

New studies reveal that to burn the most fat, you need to go 12 hours without eating—say, from 8 p.m. to 8 a.m. So it's smart to time your calorie intake accordingly. Read on for the science-backed rules that will help you use the clock to shed excess pounds.

To keep pounds off, don't eat after dark
Before electricity and all-night diners, we humans used to spend a long stretch every night without food passing our lips. "Staying up and eating late is a very recent phenomenon in human history," Panda notes. So our metabolisms are hardwired to expect a nightly fast, which is a key time for your body to burn fat.

Here's how that works: During the day, your brain and muscles use some of the calories you eat for fuel, and the rest gets stored in the liver in the form of glycogen. At night, your body converts that glycogen into glucose and releases it into your bloodstream to keep your blood-sugar levels steady while you sleep. Once the stored glycogen is gone, your liver starts burning fat cells for energy. Yes, you read that right—you burn fat while you sleep.

The catch: "It takes a few hours to use up the day's glycogen stores," Panda says. So if you snack until midnight and sit down to your breakfast of oatmeal or eggs at 7 a.m., your body may never get the opportunity to burn any fat before you start reloading your glycogen stores again.

It doesn't help that you're also likely to overeat when you're up late—indeed, night owls consume an average of 248 calories more per day than those who go to bed earlier, and most of those excess calories rack up after 8 p.m., according to a 2011 study published in the journal Obesity.

"Willpower is lower when you're sleepy," explains study author Kelly Baron, PhD, a clinical health psychologist at Northwestern University's Feinberg School of Medicine in Chicago. "So if you're eating in the middle of the night, you're more likely to overeat and make poor food choices."

On the other hand, Panda says, "eating only between 8 a.m. and 8 p.m., and then not eating for at least 12 hours, should give your body enough time to burn all of the stored glycogen plus some fat every night."

This could have major consequences for your weight and health—and mean you can snack more and weigh less. In a study just published in Cell Metabolism, Panda's research team found that mice that ate a high-fat diet spread out over the day and night became obese and diabetic, while mice eating the same diet but only over an eight-hour period didn't gain any weight and remained healthy. "Fasting at night can even override most of the negative effects of an unhealthy diet," Panda says, "including weight gain."

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Paige Greenfield
Last Updated: June 11, 2012

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