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, 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 centers on sleep, diabetes, obesity, and acid reflux.
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. They also included more than 4,100 patients from the American Gut Project, now called the Microsetta Initiative.
"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 at Baylor College of Medicine. "This is important because stress and excess late-night eating often go hand in hand."
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. The researchers also found that having both nighttime eating habits and high stress levels was associated with significantly lower diversity of bacteria in the 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." Different gut microbes also support our health in various ways — including optimizing nutrient absorption, 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. "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," said Dr. William Chey, chief of the division of gastroenterology and hepatology at Michigan Medicine.
If further research finds a causal relationship, there are several potential explanations. "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," Preidis said. A 2024 study found that limiting eating to between 9 a.m. and 5 p.m. can reduce inflammation in the gut.
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. Otherwise, your body has to divert energy from other important processes that occur during rest. 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. Lower-fat foods such as fruit, complex carbohydrates, vegetables and certain proteins are more likely to be digested faster.