It’s not uncommon to crave sweets after a poor night’s sleep. And while most people assume it’s just tiredness wearing down their willpower, a 2024 review in the Journal of Sleep Research suggests biology may actually be to blame.

Researchers parsed the results of 13 studies and found that sleeping less than 6 hours per night increases how much you enjoy sweet flavors, which likely nudges you toward sugary foods more often.

It’s not yet clear why tired brains lean toward sugar, but there are a few working theories. One is that sleep deprivation lowers dopamine—the chemical that makes pleasurable things feel good—so your brain seeks sweet foods to top up the tank. 

Another possibility is that poor sleep increases the reward value of food in general. That is, everything tastes better when you’re underslept, which makes it even harder to resist sugary fare.

These findings sit neatly alongside the growing body of evidence on how sleep affects our eating habits.

For instance, research shows that short sleep increases calorie intake and steers us toward more indulgent foods. It also shows that undersleeping disrupts hormones like leptin and ghrelin, which can make you more likely to overeat.

That helps explain why scientists now recognize insufficient sleep as a key risk factor for weight gain and obesity.

Fortunately, the fix is surprisingly low-effort.

In one study, people who slept just 20 minutes longer each night cut their daily sugar intake by nearly 10 grams. Another study found that extending sleep by just over an hour led people to eat 270 fewer calories per day—a change which quickly led to fat loss.

All of which makes a simple point hard to ignore: To make fat loss feel easier, sleep more. For most, that means getting 7-to-9 hours a night.

Scientific References +