A woman takes a donut from a fridge.

Research shows that sneaking a late-night snack can throw off your body's natural rhythms. (iStockphoto)

Breakfast, lunch and dinner do the body good. But what about a late dinner, midnight snack and middle-of-the night munching?

Research consistently shows that people who eat late at night weigh more than those who eat all of their food earlier in the day. For example, people who eat most of their food at night have higher body mass indexes than people who eat earlier in the day, according to a 2007 study published in the International Journal of Obesity. And in one study published in The American Journal of Clinical Nutrition, participants who ate between 11 p.m. and 5 a.m. gained more weight than those who kept their mouth shut during those hours.

But what is it about nighttime that makes the fat pack on?

Nothing Good Happens After 10 p.m.

“Over the years, I have reviewed research that says that only the total caloric intake ingested over the day matters,” says board-certified bariatric physician Dr. Caroline Cederquist, author of "The MD Factor Diet." “I think this is the real crux of the issue. At midnight, people will rarely make chicken and salad. They will eat ice cream or chips, the high-fat or high-sugar foods that our bodies store so effectively as fat.”

In fact, in The American Journal of Clinical Nutrition study, nighttime eaters ate 12 percent more calories than those who ate only throughout the day. And in the International Journal of Obesity study, nighttime eaters participated in more binge-eating behaviors than those who didn’t eat after dinner.

Binging on high-sugar, high-fat foods causes you to go to bed with elevated blood sugar levels. At any time of day, these set the body up for subsequent sugar crashes and weight gain, with the body quickly storing excess sugar as fat, says Lori Zanini, a California-based registered dietitian and certified diabetes educator with HealthCare Partners medical group. But, since your body uses less sugar as fuel when you’re lying in bed as opposed to running around, potentially more sugar winds up in your fat cells when you eat those foods late at night.

Throwing Off Your Rhythm

Still, the problems with late-night eating extend far past what people choose to eat before bed.

Animal research from Northwestern University suggests that eating at night can lead to weight gain – even if you don’t eat excess calories. Researchers claim this is because eating at night can interfere with the body’s circadian rhythms.

For instance, insulin – the hormone responsible for getting the sugar in your blood to your body’s cells for fuel – runs along with your circadian clock. So at night (when your body thinks you should be asleep and fasting), your body’s cells become more resistant to the hormone, according to a 2013 animal study in Current Biology. That means that eating large nighttime meals can cause especially high blood-sugar levels and, over time, fat accumulation, insulin resistance and Type 2 diabetes.

What’s more, eating right before bed can disrupt your sleep to make next-day cravings a biological inevitability. 

Eating, especially a large meal, late at night also increases your risk of heartburn. “Esophageal reflux commonly occurs when our stomachs are full and we lie down, allowing the stomach contents to reflux into the esophagus causing discomfort and affecting sleep,” Cederquist says.

She also notes that in patients who have metabolic dysfunction (common in overweight individuals) and eat high-carb meals before bed, blood-sugar levels nose-dive throughout the night. “This hypoglycemia wakes people right up from sleep and makes it hard to fall back to sleep after, disrupting normal sleep patterns,” she says.

After a bad night’s sleep, the body’s levels of appetite-triggering hormones increase, while hormones that blunt hunger drop, according to a 2013 study in The Proceedings of the National Academy of Sciences. Peoples' bodies become resistant to insulin’s effects, raising the risk of fat accumulation, obesity and Type 2 diabetes. Hence why one meta-analysis published in Sleep studying 634,511 people worldwide found that those who frequently miss out on sleep suffer from weight gain and obesity.

Eat Right at Night

“I usually recommend individuals stop eating approximately 1.5 to 2 hours before going to bed to allow for digestion. Since we digest our food better when we are upright, this allows our body to truly rest and repair while we are sleeping in preparation for the next day,” Zanini says.

“Still, even if it’s late at night, if an individual is hungry, he or she should eat. It’s important to listen to our body’s hunger cues at all times,” she says. Going hungry will set you up for low blood sugar levels, intense cravings and binging once you finally do eat.

If that’s you, fight the urge to reach for high-fat, high-sugar goods and opt for a healthy protein-packed snack. “That way, the food will be much less likely to elevate blood sugar and then cause a rapid fall in the early morning hours,” Cederquist says. Zanini recommends reaching for almonds, low-fat cottage cheese and tomatoes, Greek yogurt with cinnamon or vegetables dipped in hummus or guacamole.

Tags: weight loss, obesity, food and drink, diet and nutrition, low-calorie diet, diabetes type 2

K. Aleisha Fetters , MS, CSCS, is a freelance Health & Wellness reporter at U.S. News. As a certified strength and conditioning specialist with a graduate degree in health and science reporting, she has contributed to publications including TIME, Women's Health, Men's Health, Runner's World, and Shape. She empowers others to reach their goals using a science-based approach to fitness, nutrition and health. You can follow her on Twitter or Instagram, find her on Facebook or the Web or email her at kafetters@gmail.com.

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