Sleeping in on weekends might be linked to a higher body weight in some studies, but those studies show association, not cause, so it's a reason to look at your sleep pattern rather than to feel guilty about a lie-in. Researchers call the weekday-weekend sleep gap "social jet lag".
Pick a short workout and read on.
This isn't a claim that weekend lie-ins make you gain weight. Talk to your doctor if you have persistent sleep problems.
What social jet lag is
It's the mismatch between when your body wants to sleep and when work, family and life make you wake up. You run a sleep deficit on weekdays and try to repay it on weekends, which is a bit like flying across time zones every Friday and back every Sunday.
What the studies found
- A New Zealand study (2015, International Journal of Obesity) followed more than 1,000 people from Dunedin through their lives. As little as a two-hour gap between weekday and weekend sleep was associated with a higher BMI than in people without the gap. The lead researcher said that equated to about 2 kg more fat mass at age 38
- A 2012 German study (Current Biology) used an online questionnaire completed by more than 65,000 people and was the first to link social jet lag to obesity
The caveats, which matter
- These are associations, not proof of cause
- Science News described the link as fairly modest
- Environment, genes and behaviour all matter too
- The 2012 study relied on self-reported questionnaires
- The explanations for why (more night-time eating, hormone changes) come from other research, not from measuring them in those studies
So should you stop sleeping in?
Not necessarily. The more useful reading is: if you need a huge weekend catch-up, your weekday sleep may be too short. That's the thing to look at. Read how much sleep to lose weight and bad sleep and belly fat.
Simple ways to shrink the gap
- Keep your wake-up time within an hour or two of your weekday time
- Move your bedtime earlier on weekdays instead
- Get daylight soon after waking
- Watch late caffeine and alcohol. Read coffee before training: performance boost or sleep tax and does one beer ruin your workout
- Use the clock change sensibly. Read can daylight savings time make you gain weight
What about Sunday-night training?
Some people feel better with a routine. Read will working out at night wreck your sleep and best time of day to work out.
FAQs
Is a weekend lie-in bad?
Not inherently. It may be a sign you're short on sleep during the week.
How big a gap is a problem?
The New Zealand study found associations with a gap as small as two hours. That doesn't mean two hours is harmful for you.
Does this explain the dad bod?
It might be one small piece. Read dad bod to fit.
The bottom line
A lie-in isn't a crime, but a big weekday-weekend gap is a hint. Pick a short workout and aim for a steadier week.
Go train, FATBOY.
Sources
This article is general information, not medical advice, and the research it describes is limited and often small. Train at your own risk. If you have a health condition, take medication or are unsure whether exercise, caffeine, alcohol or a diet change is right for you, talk to your doctor first.
- sleep
- social jet lag
- weight