The late-night eating habit that may throw your gut health into chaos

(CNN) — If stress causes your digestive woes, eating late at night isn’t doing you any favors.

For thousands of participants in new, early research, those eating more than 25% of one’s daily calories after 9 p.m. while stressed were as much as 2.5 times more likely to have abnormal bowel habits like constipation or diarrhea.

The research is an abstract that hasn’t yet been peer-reviewed or published in a journal, but was presented in May at Digestive Disease Week, a prestigious annual meeting for professionals in gastroenterology, hepatology and related fields. The research was also observational, as all data points were measured at one point in time, so it doesn’t prove a causal relationship between stress, nighttime eating and gut health.

“I’m a person who myself eats a lot of times late at night, so it was just out of curiosity, and I couldn’t find a lot of articles about it,” said lead author Dr. Harika Dadigiri, explaining why she conducted the investigation. Most research on the health effects of late-night eating center on sleep, diabetes, obesity, and acid reflux or GERD (gastroesophageal reflux disease).

Dadigiri and her coauthors analyzed the health data of 11,149 participants from the 2005 to 2010 cohort of the US Centers for Disease Control and Prevention’s National Health and Nutrition Examination Survey. The researchers also included more than 4,100 patients from the 2013 to 2017 period of the American Gut Project, now called the Microsetta Initiative. More recent data didn’t have all the details the authors wanted, said Dadigiri, who is also a resident physician at New York Medical College at Saint Mary’s General Hospital and Saint Clare’s Denville Hospital, both in New Jersey.

“Few prior studies have explored the timing of meals, or the combination of stress with late-night eating, on bowel function,” said Dr. Geoffrey Preidis, associate professor of pediatrics in the division of gastroenterology, hepatology and nutrition at Baylor College of Medicine and Texas Children’s Hospital, via email.

“This is important because stress and excess late-night eating often go hand in hand,” Preidis, who wasn’t involved in the research, added.

Meal timing and the gut

In the new research, the authors defined chronic physiological stress by participants’ composite allostatic load score — which involves eight cardiovascular, metabolic and inflammatory biomarkers, such as blood pressure, cholesterol and body mass index.

Late-night eating on its own didn’t affect gut health or function, indicating that the combination with stress may be “the danger,” Dadigiri noted in her presentation.

The researchers’ analysis of the American Gut Project participants found that having both nighttime eating habits and high stress levels also was associated with significantly lower diversity of bacteria in their gut microbiome.

“The gut microbiota is the collection of all organisms — including bacteria, viruses, and fungi — that live in the intestines,” Preidis said. Highly diverse gut microbiomes “bounce back more readily from disruptions including illness, medications, or other stressors,” he added.

Different gut microbes also support our health in various ways, Preidis said — including optimizing nutrient absorption from food, regulating the immune system and communicating with our brain to control sleep and mood.

Since the study is observational, whether the gut microbiome findings were causing bowel issues or whether abnormal bowel function changed the gut microbiome is unclear, Preidis said.

There are also several important, potentially influential factors the authors didn’t have data on, said Dr. William Chey, president of the American College of Gastroenterology, via email. There could be differences between the foods consumed by people who ate at earlier times and the foods eaten by people at night.

If nighttime meals consisted of ultraprocessed foods, for example, those have been associated with frequent bowel issues like constipation, Chey, chief of the division of gastroenterology and hepatology at Michigan Medicine, said. The research also lacked details on potential medical conditions or medication use.

“These findings should be viewed as hypothesis generating and spur additional research to better understand whether meal timing might be a modifiable risk factor in patients with constipation or diarrhea,” Chey said.

However, if further research finds a causal relationship, there are several potential explanations, Preidis said. “Both the body and the gut microbiome have natural circadian rhythms that can be interrupted by changes in diet composition or timing. Disruptions might affect hormones, immune activation, gut-brain signaling, and motility of the stomach and intestines.”

Motility refers to how food moves through the digestive tract.

A 2024 study found that limiting eating to between 9 a.m. and 5 p.m. can reduce inflammation in the gut, which can lead to gut dysbiosis, an imbalance in gut microbial organisms, Dadigiri said. Having high levels of the stress hormone cortisol alone can also cause this imbalance.

Bedtime best practices

While the abstract itself isn’t enough to offer specific lifestyle recommendations, these experts do have advice that’s good to follow for your gut and other health concerns regardless.

Generally, not eating in the three to four hours before bedtime is best so there’s ample time for food to empty from the stomach, said Dr. Kyle Staller, director of the Gastrointestinal Motility Laboratory at Massachusetts General Hospital and associate professor of medicine at Harvard Medical School.

Otherwise, your body has to divert energy from other important processes that occur during rest to a digestive tract that should be inactive, Staller, who wasn’t involved in the research, said. Limiting nighttime eating also can help prevent acid reflux.

If you must eat at night, try avoiding heavy, greasy and fatty foods and keeping portions small, Staller and Preidis said. Lower-fat foods such as fruit, complex carbohydrates, vegetables and certain proteins are more likely to be digested faster.

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