How late-night eating affects your body

The human body is programmed to process nutrients during the day and conserve and store energy at night. Disrupting that routine can cause problems, according to Marie-Pierre St-Onge, a nutrition and sleep scientist at Columbia University.

Multiple studies have found that eating dinner within three hours of bedtime can worsen heartburn or acid reflux symptoms, and other limited research has suggested that eating one to three hours before bed is associated with more disrupted sleep.

Eating late at night has also been found to have a negative impact on weight and metabolic health. One study from 2019 looked at nearly 900 middle-aged and older U.S. adults and found that those who consumed around 100 calories or more within two hours of bedtime were roughly 80% more likely to be overweight or to have obesity than those who didn't. Other research from Sweden and Japan have had similar findings.

In addition, another study from 2023 of more than 850 adults in Britain found that those who regularly snacked after 9 p.m. had higher levels of HbA1c, which is a marker for diabetes risk, as well as greater spikes in blood sugars and fats after their daytime meals than those who didn't typically eat late-night snacks.

However, Frank Scheer, a neuroscientist at Brigham and Women's Hospital, noted these types of studies can't establish a causation between late-night eating and weight gain or other health issues since other factors like genetics, exercise, and sleep also have an effect.

Why?

In one trial from 2022, Scheer and his colleagues had 16 overweight or obese adults live in a laboratory where their meals, exercise, and sleep were all regimented. The participants were subjected to two different eating schedules — one where breakfast was soon after waking up, lunch was at midday, and dinner was in the early evening, and the other, where all meals were shifted four hours later, with dinner occurring around 9 p.m.

The participants in the study ate the same amounts of nutrients and calories on both eating schedules, but when they were on the later meal schedule, they reported feeling hungrier than they did on the earlier one. In addition, their levels of the hormone leptin, which signals fullness, were lower throughout the day while their levels of ghrelin, which signals hunger, were higher. They also burned fewer calories.

According to Scheer, these findings suggest that eating late at night could cause weight gain, though he noted that longer-term studies were needed.

Other research has found that consuming carbohydrates in the evening leads to greater blood sugar spikes than ones consumed earlier in the day, according to Erin Hanlon, a behavioral neuroscientist at the University of Chicago. This is partly because melatonin, the sleep-promoting hormone that increases at night, slows the secretion of insulin which regulates blood sugar levels, Hanlon said.

According to St-Onge, elevated blood sugar levels could damage blood vessels and increase a person's risk of developing high blood pressure and Type 2 diabetes.

How to time late eating

If possible, you should avoid eating three to four hours before your typical bedtime, St-Onge said. Hanlon added that timing is likely better for your long-term health and could reduce acid reflux symptoms, which can interfere with sleep.

If you're a shift worker, eating late at night could be unavoidable, but, if possible, Scheer recommends eating your largest meals between 7 a.m. and 7 p.m.

Timing when you eat and sleep can be "a little bit of a juggling act," St-Onge said, as you don't want to eat a large meal too close to bedtime, but you also don't want to go to bed hungry.

Scheer noted, however, that some people, like those who have low blood sugar or don't get enough nutrition, may still need to eat at night.

If you have to eat later at night, St-Onge recommends eating something smaller and more nutritious that isn't high in fat or added sugars, like plain yogurt with fruit, vegetables with hummus, or almond butter on whole grain toast. (Callahan, New York Times, 12/19)

Writing for the New York Times, Alice Callahan outlines 10 science-backed nutrition tips to help you start eating healthier.