3 Worst Foods That Cause an Unhealthy Gut, from a Seattle Gastroenterologist

Updated: May 23, 2024

A Seattle-based gastroenterologist shares the three types of foods known to create an unhealthy gut microbiome, all linked to major health concerns.

breakfast sandwich with sausage
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The “gut” may seem like a simple term, but it actually involves numerous parts of the body connected to the digestive and gastrointestinal tracts, as well as the microbiome. The gut microbiome is made up of trillions of bacteria and microorganisms inside the large intestine, and having a diverse set of bacteria is key for keeping different bodily functions working properly such as the nervous system, immune system, digestive function and even our mental health. What we eat plays a major role in the health of the gut microbiome, and certain foods can harm your gut health. According to Chris Damman, MD, MA, a board-certified gastroenterologist at the University of Washington in Seattle and the chief medical and scientific officer at Supergut, if you’re not feeding your gut properly, you could be facing some major health concerns down the line.

“The foods you eat determine the type of bacteria that grow in your gut,” says Dr. Damman. “Healthy foods that grow healthy bacteria will make factors that grow healthy gut cells. This means less ‘leaky gut,’ less inflammation, and a healthier body overall.”

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Nevertheless, while indulgence is fine once in a blue moon, there are certain types of foods that can harm your gut when consumed on a regular basis by creating an unhealthy environment for your gut’s bacteria. Dr. Damman shares three foods to be wary of if you’re looking to keep your gut health in check.

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four Gourmet Cupcakes
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Refined baked goods

While packaged and refined baked goods—like store-bought pastries, white bread and bagels—can make for a treat in the morning, many gut health specialists, like Dr. Damman, consider these to be foods that can harm your gut.

“Especially those containing high fructose corn syrup should be avoided,” Dr. Damman says. “These foods are missing fibers that are transformed by gut bacteria into molecules that grow healthy colon cells and protect your body from obesity and diabetes. Better options (in moderation) are baked goods that contain whole grains, and that are missing high fructose corn syrup in their ingredient list.”

Having a sufficient amount of dietary fiber in the diet (which the 2020-2025 Dietary Guidelines for Americans suggest 25 to 30 grams a day) is important for keeping the bacteria in the gut fed. When the bacteria in the gut aren’t fed, a 2021 peer-reviewed study in Nutrients suggested there can be an increased risk for gut-related diseases, including inflammatory bowel disease, obesity, type 2 diabetes, and metabolic syndrome.

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Preparing a Monte Cristo Sandwich, with Black Forest Ham, Smoked Turkey Breast, Cheddar and Swiss Cheese
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Processed meats

Dr. Damman says, “Bacon, hot dogs, beef jerky and lunch meats are associated with a higher risk of colon cancer because the natural components and additives get transformed into carcinogens during the cooking process.” He adds: “A better option (in moderation) is meat from the butcher, especially white meat or low amounts of grass-fed meat that contain higher amounts of good fats.”

According to a 2021 University of Washington School of Medicine study, an increased presence of certain types of unhealthy bacteria has been linked to an increased risk of colon cancer, indicating a greater likelihood that colon polyps will become cancerous.

A 2021 review in BMC Cancer affirmed these findings and stated that the gut microbiome has important clinical implications for colorectal cancer prevention, while modulating the gut microbiota is important not only for cancer risk, but also for the individual’s overall health.

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Glass of coke and pizza
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Sugary drinks

Sugary drinks go beyond just sodas—even juices and some diet sodas can harm your gut, especially if they contain high fructose corn syrup, saccharin, or sucralose.

“These drinks can grow unhealthy bacteria in your colon and cause diarrhea, as well as diabetes and obesity,” says Dr. Damman. According to a recent 2022 review in Clinical Gastroenterology and Hepatology, both hyperglycemia (high blood glucose levels) and excessive sugar intake can disrupt the intestinal barrier, which increases gut permeability and can cause gut microbiota dysbiosis—an imbalance of bacteria in the gut, which can have negative implications.

“Better options are satisfying cold water as well as unsweetened teas and coffee. If you do use a sugar substitute, allulose is one that might be more associated with [better] health.”

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