You’ve tried everything to lose weight: portion control, fasting, liquid diets, even eating meals on a treadmill. Now, a new study suggests that maybe you should try turning out the lights. Because, at least in mice, exposure to light at night leads to weight gain. The work appears in the Proceedings of the National Academy of Sciences. [Laura Fonken et al., “Light at Night Increases Body Mass by Shifting the Time of Food Intake“]

Obesity is an epidemic. Maybe it’s because we eat too much and spend too much time in our seats. But another factor could be that these days we’re never really in the dark. Streetlamps and indoor light sources now brighten our nights. And that light pollution could be messing with our circadian rhythms, which control not only sleep, but metabolism. In fact, mutant mice that have no circadian clocks tend to be chunky.

To test the connection between photons and fat, scientists took mice and lit up their cages. And they found that mice that were exposed to even dim light at night were chubbier than mice who spent their evenings in the dark. Though they all ate the same amount, the fat mice snacked more when they were less active, perhaps failing to burn off those calories.

So maybe skip the night light. Especially the one that lights up when you open up the fridge.