Is the lighting in your house sabotaging your weight loss?

It can be hard to lose weight. And it can be even harder to stick with your goals when your actions aren’t paying off. You might pile your plate with vegetables or step out for a walk every chance you get. Yet the number on the scale just won’t budge.

So what gives? Well, it turns out that your indoor environment could be a key factor in your stalled results. A 2022 study in the journal Diabetologia suggests that the intensity of light you experience during the day can affect your metabolism.

Researchers gathered 14 volunteers between the ages of 40 and 75 who were at risk of developing Type 2 diabetes. Then they split them into 2 groups. The first group spent their day, from 8 a.m. to 6 p.m., in a well-lit room. Then at 6 p.m., the lights were dimmed until 11 p.m., when they went to sleep. The second group had the opposite experience. They spent their day in dim light. Then they were exposed to bright light before bed, from 6 p.m. to 11 p.m.

The researchers then looked at the participants’ metabolism. They found that the first group burned more calories during the day and at night than their peers. Their blood sugar was also lower going into dinner than the dim-light day group. And they had higher amounts of melatonin in their systems before bed. Melatonin is a hormone that plays a key role in the body winding down for sleep.

Overall, people who spent the day in a bright room followed by dim evening light naturally burned more calories than those who didn’t. No extra steps or calorie-cutting was needed.

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While this small study was just a day long, imagine the long-term effects it could have on your weight. “If you spend weeks or months in suboptimal lighting, it could contribute to weight gain,” says Jan-Frieder Harmsen, who was the lead author of the study. He’s a PhD student at Maastricht University in the Netherlands.

How indoor lighting can affect weight

Well, it likely has a lot to do with sleep. Light is the main regulator of the body’s internal clock, explains Steven Henry Feinsilver, MD. He’s a New York-based physician with Northwell Health who specializes in sleep medicine. Light plays an important role in how much — and how well — we sleep. And that can influence our hunger hormones and how much energy our bodies burn at rest.

“Sleep-deprived people are prone to gaining weight,” says Dr. Feinsilver. You may have even experienced this. One bad night of sleep and you’re likely to have a bigger appetite the next day.

When indoor lighting patterns mimic the natural rising and setting of the sun, our hormones are more in balance. And that means we’re more likely to get better sleep.

But in the modern world, it can be hard to stick to that cycle inside. Here, experts share their tips on optimizing your indoor lighting. That way, there will be one less thing standing in the way of quality sleep — and your weight-loss goals.

Recommended reading: Your guide to anti-obesity weight-loss medications.

First thing in the morning: Open the curtains

“Light is the natural thing that turns your brain on,” says Dr. Feinsilver. He tells people with sleep troubles to expose themselves to light first thing in the morning. “I would like you to get up and go outside almost immediately, as fast as you can,” he says.

Go for a walk, then go in and have breakfast. “Light, food and exercise are the main things that regulate our body’s clock,” adds Dr. Feinsilver. So doing those actions together is an added calorie-burner bonus. Aim for 20 minutes of morning light. (And adding even 10 minutes of activity to your day can prolong your life.)

No time for a jaunt? Simply sit or stand outside while you eat breakfast. And if you’ve risen before the sun, turn on as many lights as you can. Or you can buy a light box. Choose one that’s designed to provide full-spectrum light. “You can turn that on while you’re having breakfast and park yourself near it,” says Dr. Feinsilver.

During that midafternoon energy slump: Get outside

Do you reach for coffee or candy to stay alert during the post-lunch slump? Consider a dose of sunlight instead. According to the Centers for Disease Control and Prevention, white light can help you feel more alert. And it may even brighten your mood.

“In your office, you could try to sit closer to the window, too,” says Harmsen. Or you can increase the brightness level of your artificial lighting. Just keep the brightness realistic. “Be sure it’s not too bright to perform work and that it isn’t harsh on the eyes,” he adds.

After sunset: Start dimming the lights

“After dinner, it’s time to dim your environment,” says Dr. Feinsilver. The critical time for sleep preparation is the hour before you go to bed, he says: “Read if you want, but don’t use personal electronics.” And, of course, keep your room relatively dark.

White light from lamps and blue light from electronics can both make it tough to fall asleep and stay asleep. Experiment with using red- or orange-hued lights for reading. And if you can’t help but scroll on your phone, activate its nighttime mode first. The iPhone’s Night Shift feature, for example, lowers blue light from the device in the evening, Dr. Feinsilver says. You can also buy blue light-blocking glasses.

That said, Dr. Feinsilver warns that interacting with any device can keep your brain awake. So it might be best to just curl up with a good book instead.

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