Is ‘Social Jet Lag’ Making You Fat?

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If your sleep schedule differs between the weekends and weekdays, you’re likely experiencing what researchers call “social jet lag” and it could be making you fat.

Social jet lag, a term coined by researchers in Europe, refers to the discrepancy between your natural body clock and your social clock — the schedule you need to keep for your job and other social commitments. If you’re relying an alarm clock to wake up every morning during the week, but sleeping in on weekends, that’s a good sign there’s a mismatch. The end result is that your body’s basically shuttling back and forth between time zones each week while you’re becoming increasingly sleep-deprived.

“While during the workweek [people] get too little sleep and are woken by the alarm clock in the middle of their biological night, they sleep in on the weekends in order to fill up their tanks with the sleep they need,” researcher Dr. Till Roenneberg of the University of Munich’s Institute of Medical Psychology, in Germany, said in a video about the study.

(MORE: Getting More Sleep at Night May Help You Keep Slim)

The consequences of inadequate sleep can be far reaching. In Roenneberg’s study, researchers surveyed the sleep habits of more than 65,000 adults and found that people whose weekend and weekday sleep schedules differed were three times more likely to be overweight than those who went to bed and awoke at the same time each day. The greater the difference between weekend and weekday sleeping, the fatter people were.

Although the new study doesn’t prove that sleep-deprivation directly causes weight gain, the findings fall in line with a growing body of evidence that associates the two. Many studies have linked inadequate sleep with a variety of health problems, including obesity, depression and chronic diseases like diabetes — especially among shift workers. One recent study found that workers increased their risk of developing diabetes by 5% if they maintained a rotating night-shift schedule for 1 to 2 years; working nights for at least 10 years led to a 40% increase in diabetes risk.

Part of the problem is that when people are awake when they should be sleeping, they tend to eat less healthily — and they’re also eating when their bodies don’t want to be, which contributes to weight gain. Sleepy people are also less likely to exercise and more likely to drink alcohol, rely on caffeine and smoke.

Further, disrupted sleep wreaks havoc on the body’s metabolic processes: it lowers people’s resting metabolic rate — which could set the body up for a 10-lb. gain within a year, according to a recent study — and reduces the amount of insulin the body produces. Both factors can push people toward diabetes.

(MORE: A History of Kids and Sleep: Why They Never Get Enough)

Roenneberg suggests that acknowledging people’s individual sleep-wake cycles could make for a healthier population and economy. reports:

Rather than bending early birds and night owls to the same work schedule, why not encourage personalized schedules based on each individual’s circadian rhythms? The result would be a better-rested, healthier, and doubtless more productive workforce, Roenneberg says.

That sounds great, but it’s probably unrealistic. Getting a full night’s rest every night is also probably unrealistic for many among the overstretched American workforce. But, as much as possible, experts encourage people to adjust their sleep schedules — going to bed and rising at the same times each day — to make sure they’re getting as close to the recommended 7 to 9 nightly hours as they can. (Click here for tips on good sleep hygiene from the National Sleep Foundation.)

“Waking up with an alarm clock is a relatively new facet of our lives,” said Roenneberg in a statement. “It simply means that we haven’t slept enough and this is the reason why we are chronically tired. Good sleep and enough sleep is not a waste of time but a guarantee for better work performance and more fun with friends and family during off-work times.”

(PHOTOS: The Artistry of Sleep: Photos of Icons Getting Some Shut-Eye)

The study is published in the journal Current Biology.