Had trouble sleeping last night? You may want to avoid going grocery shopping today.
According to a new study from Sweden, when we’re sleep-deprived, we end up buying more food overall and more high-calorie foods in particular than we do after a good night’s rest.
Other, earlier studies have shown that we tend to eat more food than usual — particularly high-calorie snacks — after we’re up all night. But this new study suggests that sleep deprivation has an even longer effect on our dietary habits by influencing what we bring home from the grocery store and put in our refrigerators and pantries.
For the study, the researchers recruited 14 healthy, normal-weight men in their early 20s. None had any reported sleep problems. The young men were brought into a sleep lab on two occasions, a month apart. During one of the visits, they were kept awake throughout the night; during the other, they were allowed to sleep.
In the morning, the participants were offered a full breakfast to ensure that they wouldn’t be hungry. (Interestingly, as predicted from previous studies, the young men tended to eat larger portions of food after being deprived of sleep than they did after getting a full night’s sleep.) Then the men were given the equivalent of about $50 and instructed to spend all of it in an online grocery store. The “store” had 40 items, including 20 high-calorie foods and 20 low-calorie ones.
On the morning after they were kept awake all night, the participants purchased an average of 9 percent more total calories and 18 percent more total grams of food with their money than they did after a night of laboratory sleep.
This finding suggests, according to the study’s authors, “that increased food purchasing in the morning after nocturnal wakefulness may represent another mechanisms through which a repeated or chronic lack of sleep, e.g., through shift work, promotes weight gain.”
“Our findings are broadly significant,” they add, “for people working in a variety of professions, including shift workers, cab drivers, nurses, doctors, and other jobs requiring work at night.”
More vulnerable to impulsive decisions
The study also found that sleep deprivation causes blood levels of the hormone ghrelin, which is suspected of increasing hunger, to rise. But no direct correlation was observed between ghrelin levels and the amount of food purchased by the study’s participants.
That suggests, say the study’s authors, that other factors are involved. Indeed, research involving functional magnetic resonance imaging (fMRI) has suggested that sleep deprivation leaves the brain more vulnerable to impulsive decision-making.
In other words, when we’re tired, we’re less likely to be able to resist slipping a candy bar or six-pack of sugary soft drinks into our grocery cart.
Like all studies, this current one has its limitations. Most notably, it’s a very small study and involves only young men living in Sweden. The findings may or may not hold up in larger and more diverse groups.
Still, it’s always a good idea to keep your wits about you while grocery shopping — and especially, perhaps, after a bad night’s sleep.