Is It Bad to Eat Late at Night?

Q: I’ve heard that eating too late in the evening is bad for your health. Is this true?

Many of us reach for comfort foods like ice cream and leftover takeout after a long day. But if you make late night snacking a regular habit, it could have unintended consequences on your health, experts say.

According to a recent study of the eating habits of more than 34,000 U.S. adults, nearly 60 percent said it was normal for them to eat after 9 p.m.

Our bodies have evolved to process nutrients during the day — and to conserve and store energy at night, said Marie-Pierre St-Onge, a nutrition and sleep scientist at Columbia University. And disrupting that natural rhythm could cause problems, she said.

Several studies have found, for instance, that eating dinner within three hours of bedtime may worsen heartburn or acid reflux symptoms.

And limited research has suggested that eating one to three hours before bedtime is associated with more disrupted sleep.

The most intriguing research on late-night eating, however, has focused on its relationship with body weight and metabolic health, said Frank Scheer, a neuroscientist at Brigham and Women’s Hospital in Boston.

In one 2019 study of nearly 900 middle-aged and older U.S. adults, for instance, Dr. Scheer and his colleagues found that those who consumed roughly 100 calories or more within two hours of bedtime were about 80 percent more likely to be overweight or to have obesity than those who did not eat during that window. Researchers have found similar results in adults in Sweden and Japan.

And in a 2023 study of more than 850 adults in Britain, those who regularly snacked after 9 p.m. had higher levels of HbA1c, a marker for diabetes risk, and greater spikes in blood sugars and fats after daytime meals than those who did not typically consume late-night snacks.

Such studies can’t prove that late-night eating directly causes weight gain or other health problems, because other factors, such as our genetics, exercise and sleep are also involved, he said. But recent research that controls for these factors has started to reveal direct effects of meal timing on health.

Why late eating might be harder on your body

In a 2022 trial, Dr. Scheer and his colleagues asked 16 overweight or obese adults to live in a laboratory where their meals, exercise and sleep were carefully regimented. All of the subjects followed two different eating schedules, each for six days: One schedule allowed for breakfast soon after waking, lunch at midday and dinner in the early evening; and the other shifted meals four hours later, with supper around 9 p.m.

The participants consumed the same amounts of nutrients and calories on both routines. Yet, on the later meal schedule, they felt hungrier than they did on the earlier one. At the same time, their levels of the hormone leptin (which signals fullness) were lower throughout the day, and their levels of ghrelin (which signals hunger) were higher.

They also burned fewer calories. And several other small studies have found that people burn less fat on a late eating schedule.

Together, these findings suggest that late-night eating could cause weight gain, Dr. Scheer said, though longer term studies are needed.

Research has also found that carbohydrates consumed in the evening result in greater blood sugar spikes than those consumed earlier in the day, said Erin Hanlon, a behavioral neuroscientist at the University of Chicago. That is in part because melatonin, a sleep-promoting hormone that increases in the evening, dampens the secretion of insulin, which regulates blood sugar levels, she added.

Elevated blood sugars could eventually damage blood vessels and increase the risk of developing high blood pressure and Type 2 diabetes, Dr. St-Onge said.

How to time your nighttime eating

Research suggests that, if possible, it’s best to avoid eating for three to four hours before your usual bedtime, Dr. St-Onge said.

That timing is likely better for your long-term health, and may also reduce symptoms of acid reflux, which can interfere with sleep, Dr. Hanlon added.

If you are a shift worker, eating late at night may be unavoidable. But, if you can, Dr. Scheer said, try to eat your largest meals between about 7 a.m. and 7 p.m.

Timing your eating and sleeping can be “a little bit of a juggling act,” Dr. St-Onge said. You don’t want to eat a large meal too close to bedtime, but you don’t want to go to bed hungry either.

Dr. Scheer also cautioned that some people, such as those who struggle with low blood sugar or with getting enough nutrition, may need to eat at night.

If you do eat later in the evening, Dr. St-Onge suggested opting for smaller, more nutritious meals or snacks that aren’t very high in fat or added sugars, such as plain yogurt with fruit, vegetables with hummus or almond butter on whole grain toast.