Winter weight gain is practically inevitable. Despite resisting Christmas cookies daily and sticking to your workout routine, your jeans always seem to get just a little tighter until the weather warms up. A breakthrough study revealed a new potential reason you gain weight when it’s cold—and it has nothing to do with the holiday season (though these 20 tips can help you beat holiday weight gain).
For a new study in Scientific Reports, University of Alberta researchers put some fat cells under lamps giving off blue light (the shortest visible light to come from the sun) for four hours and kept other samples in the dark. After two weeks, the fat cell groups had some remarkable differences.
By the 11th day, the blue light-treated fat cells had fewer lipid droplets—organelles that store fat—than the cells that didn’t get any light. What’s more, the lipid droplets in the light-treated cells were also smaller than the ones in the placebo group. “In other words, our cells don’t store as much fat,” senior study author Peter Light, PhD, tells the University of Alberta. On the flip side, less light means more fat storage, which could explain why people gain weight during the short winter months, he says. (Thankfully, these 11 tips can help you lose weight in the winter.)
While more studies are needed and the researchers haven’t pinned down why light affects fat storage, the study authors have a theory. Blue light gets its reputation mainly from electronic screens and how they signal you to keep awake at night. Now the researchers speculate that blue light might tell your body how to store fat, too. During the winter, when days are shorter and temperatures are colder, your body is programmed to store fat; with more sunlight in the summer, your body burns it off again.
The researchers hope the findings could lead to weight-loss innovations but warn not to try shedding pounds just by spending extra time in the sun. “For example, we don’t yet know the intensity and duration of light necessary for this pathway to be activated,” says Light, a professor of pharmacology and the director of the University of Alberta’s Alberta Diabetes Institute. In the meantime, stick with these 50 doctor-approved tips for losing weight.