How Screwy Weekend Eating May Wreck Your Metabolism

Yes, the weekends are for relaxing — but letting your diet slide could spell trouble come Monday. In a new study in the journal Cell Metabolism, researchers found that “metabolic jet lag” — a state of internal mayhem caused by switching both mealtimes and the number of hours during which you eat each day — is a common phenomenon after weekends, when all-over-the-place eating is the unfortunate norm.

Although we’ve all heard the three-square-meals-a-day advice — or, alternately, to eat at more frequent but still regular intervals — most of us are actually doing a pretty poor job of eating by the clock: In the Salk Institute study, people consumed less than a quarter of their calories before noon and took in more than a third of their calories after 6 p.m. And with some study participants chowing down as often as 11 times a day, the average day of eating lasted about 14 hours for half the people in the study. That’s like eating on and off from 9 a.m. until 11 p.m. every single day.

In other words, many of us are in the habit of grazing — and we’re doing it almost every waking hour.


Are your bad habits on the weekend sending your body into a metabolic tailspin? (Photo: iStock)

Constant eating doesn’t equal consistency — in fact, the researchers called most people’s eating patterns “erratic.” On average, people in the study ate breakfast on weekdays at 9:21 a.m. — a little more than an hour after waking — but moved their first mealtime to 10:26 a.m. on weekends. Some folks delayed their morning meal by even more on their days off, with a quarter of people consuming breakfast more than two hours later on weekends than on weekdays.

Over the weekend, people tend to eat for a longer stretch of the day but begin their feasting later, says lead study author Shubhroz Gill, now a researcher at the Broad Institute of MIT and Harvard’s Center for the Science of Therapeutics. “So they start two or three hours later, then go until midnight or 1 a.m., because they typically stay up longer on a Friday or Saturday night,” he tells Yahoo Health.

That may not sound like a big deal, but our bodies really aren’t designed to be flexible. “Before we had electricity, before everybody was going to work Monday through Friday, taking the weekend off, there was no difference between a Monday and a Sunday,” says Gill. “The waking and sleeping times were primarily governed by sunset and sunrise times.” By contrast, our work and social obligations now drive our daily rhythms, leaving our bodies to try to guess what our ever-changing schedule will be for the day.

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Constantly switching your eating schedule throws off your body’s internal timing. “We now know that there are clocks everywhere [in our body],” including in the liver, says Satchidananda Panda, co-author of the study. If you normally eat breakfast at 8 a.m., your liver is “ready to digest food and send the nutrients to different parts [of the body]” at that time every day.

So when you eat breakfast two to three hours later on the weekend, you totally throw off your system. “It’s not getting the nutrients at the right time,” Panda says. As a result, when Monday rolls around, your liver has adjusted and is anticipating food hours later — but then you revert back to your earlier schedule, confusing your body yet again and sending it into a state of metabolic jet lag.

The long-term consequence? Mouse studies suggest that metabolic jet lag could predispose people to metabolic syndrome, a cluster of health issues like diabetes, obesity, and high blood sugar, says Gill.

“[Metabolic jet lag] amounts to taking a flight that’s two to three hours long twice a week,” says Gill. Or as Panda puts it, “The weekend eating habits mess up our clock for nearly half of the week.” That means genes that control things like the breakdown of toxins aren’t being turned on at the right time.

And as most of us can attest, shifting mealtimes isn’t the only dietary sin we commit on our days off. A 2014 study found that people weigh the most on Sundays and Mondays, with the number on the scale beginning to creep up as soon as the weekend begins. The explanation is obvious: Weekends = cheat days.

In fact, calorie intake tends to peak on Saturdays — on average, people consume 10 percent more calories on Saturday, compared to weekdays — and the majority of us are at our most sluggish on Sundays, according to a 2008 study in the journal Obesity. If you don’t compensate later in the week, this bad habit invariably adds up to weight gain in the long term — another contributing factor to metabolic syndrome.

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You don’t necessarily have to consciously control your calorie intake on weekends, though. Avoiding metabolic jet lag by limiting yourself to an eight- to 12-hour eating window — and sticking to the same time frame every day of the week (e.g., 8 a.m. to 7 p.m.) — may do the trick.

In the study, people who reduced their daily eating duration from 14 hours to 10 to 12 hours also decreased their calorie consumption by 21 percent — without purposefully trying to cut back. “There are foods which are only consumed at preferred times,” says Gill. So if you limit your feeding window, those time-sensitive foods and drinks — think coffee and cocktails — that you would normally consume at a certain time of day may be naturally eliminated, thereby reducing your calorie intake.

And the benefits to your body are big. When people who normally ate over a period of more than 14 hours a day cut down their eating window — and stuck to that range even on weekends, while also keeping mealtimes fairly consistent — they lost an average of more than seven pounds in 16 weeks. They also felt more energized, reported less hunger at bedtime, and thought the quality of their sleep improved.

Plus, “If you’re eating only for 10 hours every day, you have 14 hours of fasting guaranteed,” says Gill. “There are known benefits of fasting” — namely, weight loss and a reduced risk of metabolic syndrome — “so you’re able to get those benefits of fasting on an everyday basis.”

Ready to fight metabolic jet lag — and do your body some serious good? Try this two-pronged plan:

Time your eating

If you don’t have any significant health problems (like diabetes, for example), pick a daily window of eight to 12 hours during which you eat — and stick to it even on the weekends. “Some people [choose to eat] breakfast at 8 o’clock and eat only until 6 p.m.,” Panda says. “And some people pick breakfast around 10 or 11 and eat until 8 or 9 p.m.” Simply choose the time frame that is most realistic for you, depending on your work schedule and natural preferences. “The only thing recommended in the other hours is water,” says Gill. “Even tea or coffee is not to be consumed.”

Want some wiggle room on the weekends? Try to stay within one hour of your set mealtimes — that is, if your weekday breakfast time is 8 a.m., make it no later than 9 a.m. on the weekends. “The liver clock can adjust if it is one hour delayed,” says Panda. “It’s almost like daylight saving time — one hour is not that bad.” By contrast, a three-hour delay in mealtime can throw your system seriously out of whack, he says.

Afraid you’ll always be hungry? Typically, it takes only a day or two — one week maximum — to adjust, says Gill. After that, “It becomes almost natural.”

Don’t skimp on sleep

If you find yourself wiped out on the weekends — and forced to compensate for a shortage of weekday shuteye — it may be time to reevaluate your bedtime. “Try to get a little bit more sleep during the week, so you’re not forced to wake up late [on the weekend],” Panda says. That way, you’ll be more likely to adhere to the eating schedule you’ve chosen every day of the week.

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