There are lots of reasons not to eat late at night as a way to cope with stress: Research has shown that the habit can interfere with your body’s natural rhythms, disrupting your sleep and increasing your risk of weight gain.
Now new research has uncovered another reason to avoid late-night snacking: It can mess up your gut health and lead to digestive issues.
For some, the stress these digestive issues cause could lead to a self-perpetuating cycle, says Ashkan Farhadi, MD, a gastroenterologist at MemorialCare Orange Coast Medical Center in Fountain Valley, California, who wasn’t involved in the study.
“When you eat close to bedtime, the gut is not happy with you,” Dr. Farhadi says. “When your gut is not happy, it will make you miserable.”
Experts say this association isn’t a coincidence. Here’s why.
The Study Analyzed Data on the Gut Health and Eating Habits of More Than 15,000 People
For the study, researchers analyzed data from more than 15,000 adult participants from two long-term studies: the National Health and Nutrition Examination Survey (NHANES) and the American Gut Project. They zeroed in on late-night snackers, defined as adults who ate more than 25 percent of their daily calories after 9 p.m.
For the first phase of the study, researchers analyzed NHANES participant health metrics linked with chronic stress, including blood pressure, cholesterol, and body mass index. Participants also reported the quality of their poop using the Bristol Stool Chart.
This widely used tool rates feces on a scale of 1 to 7, based on shape and consistency. Type 1 looks like hard lumps or small pebbles, and suggests constipation. On the far end, type 7 is loose and watery, suggesting diarrhea. Gastroenterologists consider types 3 and 4, in the middle, as the ideal.
The researchers discovered that people with high stress measurements in the first phase of the study who said they ate more than 25 percent of their daily calories after 9 p.m. were 1.7 times more likely to have constipation and diarrhea, compared with participants who had lower stress measurements and less late-night eating.
The Researchers Also Looked at the Health of Participants’ Gut Microbiome
Participants were 2.5 times more likely to report bowel issues like constipation or diarrhea if they were stressed and ate late at night. This group also had significantly lower gut microbiome diversity, suggesting that stress combined with snacking late at night may affect the gut microbiome more than stress alone.
“It’s not just about late-night snacking,” says lead study author Harika Dadigiri, MD, a resident physician at New York Medical College at Saint Mary’s and Saint Clare’s Hospital. “When you’re already under chronic stress and doing late-night snacking, it might interrupt your circadian rhythm and lead to a change in bowel habits.”
How Late-Night Snacking May Affect Bowel Regularity
The study didn’t explore the link between stress, late-night snacking, and gut microbiome changes, but there are a few theories.
After you eat, your intestines shift into a digestive mode, Farhadi explains. “There’s movement in the gut, nutrient absorption. It’s a lot of work for the gut,” he says. About three hours after that, once digestion is finished, your gut shifts into what’s called migrating motor complex, or MMC, which Farhadi describes as housekeeping for the gut.
This sweeps bacteria, food, and other debris toward your colon, and repeats the process every 90 to 120 minutes, Farhadi says. “It cleans up the digestive tract and gets it ready for the next day,” he says.
But when you eat a late-night snack, this digestive tidying gets delayed, and then interrupted by sleep. “Then, you are reducing the housekeeping of the gut,” Farhadi says. This can lead to bacterial overgrowth in the intestine, which raises the risk of constipation and diarrhea, he explains.
Marie Borum, MD, MPH, director of the division of gastroenterology at George Washington University Medical Faculty Associates, says late-night snacks can “exaggerate” the impact of stress on the gut and change your gut microbiome, ultimately affecting how your gut functions, she says.
The Type of Snack May Matter
Snack choice may also play a role in how disruptive nighttime snacking can be. “If the food is greasy, the digestion takes much longer,” Farhadi says. That means your gut will shift into “housekeeping mode” that much later, he adds.
“Foods that are high in salt, fat, and sugar can be very taxing on the gut and not optimal for promoting restful sleep and gut health,” Cording says.
Limitations to Consider
The study relied on self-reported data about diet and snack timing, which opens it up to biases and inaccuracies. Additionally, while the Bristol Stool Chart is commonly used in the medical field to track stool characteristics and changes, it can be subjective and the numbers were self-reported.
The Best Time for Your Last Snack of the Day
Dr. Borum recommends eating your last food of the day earlier in the evening, if you’re able. “Not eating three to four hours before bedtime can enhance digestion and is an effective strategy to align with natural circadian rhythm,” she says.
If you get hungry after your last meal and feel like you need to eat something, Cording suggests having something that’s easy to digest, like a banana, hard-boiled egg, or small bowl of oatmeal.
If you’ve tried this and you’re still struggling with constipation or diarrhea, Farhadi recommends seeing a doctor for an evaluation.
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