The cycle of light and darkness affects our metabolism and our digestion. So you’d expect it to have some role in dieting and weight loss too.

For years, dieters have been taught that when you eat matters. (“Don’t reach for that pint of ice cream late at night!” – good advice even though at least one of us doesn’t like to follow it.) New research suggests that it’s not only the relationship between eating and sleeping that matters, but also when you get bright light.

It’s a question light researchers have wondered about that for a long time. After all, increased appetite and weight gain are a regular part of SAD and winter blues. Up to now, there was one placebo-controlled study that showed a clear benefit from adding morning bright light to a weight control program. 34 overweight women in Novosibrisk, Russia (southwestern Siberia) were given three weeks of treatment with a light box (or a “sham” treatment) between November and April. The result? Bright light helped reduce both body fat and appetite. Most interesting, the benefit was there even for woman who experienced no seasonal change in their mood.

But most of us have never experienced a Siberian winter. Maybe what happens in Siberia during the winter is different from what happens in other, gentler climates. A new study out of Northwestern University supports the connection between light and weight. Like Siberia, Chicago may not have the kindest winters, but the Northwestern study (published in PLOS One) sampled both men and women through all four seasons. It looked at the relationship between BMI (body mass index) and light exposure. Independent of activity level, calorie intake, and sleep, bright light early in the day (before noon) was associated with lower BMIs. So far, that’s just a correlation, but it certainly helps the argument that early morning light is good for weight control. And when you get that light while walking, running or biking outside, you’ve got two powerful weight control strategies going for you.

As the study’s senior author Phyllis Zee, Professor of Neurology at Northwestern University Feinberg School of Medicine, puts it, “The message is that you should get more bright light between 8 a.m. and noon.” We explain this further on our FAQ page and in our YouTube videos; we encourage you to take a look!