Walk into a typical supermarket in the United States, and much of what you see — breakfast cereals, frozen meals, processed meats, soda — is considered ultra-processed foods.
These products, defined as foods and beverages made with ingredients that cannot be found in the home kitchen, account for more than half of the calories people consume in the United States, and have been linked to several health conditions, including obesity and type 2 diabetes.
Now, evidence has also linked ultra-processed foods to poor gut health, says Kevin Whelan, professor of dietetics at King’s College London.
What studies suggest
In recent years, a growing body of research suggests that people who eat more ultra-processed foods have a greater risk of developing certain conditions that affect the stomach and intestines.
The most consistent link is Crohn’s disease, an inflammatory bowel disease that causes abdominal pain, severe diarrhea, fatigue, and weight loss, Whelan says.
In a review published in 2023, scientists found that adults who ate the highest amount of ultra-processed foods were 71% more likely to develop Crohn’s disease than those who ate the least.
Other research has linked ultra-processed foods to an increased risk of irritable bowel syndrome, stomach ulcers, and colorectal cancer. In a study of more than 29,000 nurses published this month, researchers reported that those who ate the highest amount of ultra-processed foods were 45 percent more likely to develop a certain type of precancerous colorectal polyp than those who ate the least.
Most of these studies were observational, meaning they were able to find associations between eating patterns and health conditions, but they couldn’t prove that these eating patterns caused the conditions, Whelan says.
However, the associations are impressive and very consistent, says Andrew T. Chan, MD, a gastroenterologist at Brigham General’s College and professor of medicine at Harvard Medical School.
How ultra-processed foods can cause harm
When ingredients like wheat, oats and corn are processed into products like breakfast cereals, sliced bread and crackers, they lose beneficial fiber and healthy plant compounds called polyphenols.
Fiber and polyphenols feed the good microbes in our gut, which prevents inflammation and keeps the gut lining healthy, says Chris Daman, MD, clinical assistant professor of gastroenterology at the University of Washington School of Medicine. When these healthy ingredients are removed during processing, these benefits disappear.
Ultra-processed foods are often high in added sugars — which have been linked to an increased risk of colorectal cancer and inflammatory bowel disease (IBD) — and sodium — which can increase bad bacteria in the gut and play a role in IBD.
Additives like emulsifiers and artificial sweeteners can also harm gut health, says Neeraj Narula, MD, a gastroenterologist and assistant professor of medicine at McMaster University in Ontario, Canada.
Researchers are particularly concerned about emulsifiers, which are found in many ultra-processed foods, including some breads, salad dressings and dairy products.
Some small human studies have shown that emulsion consumption is associated with potentially harmful changes in the microbiome, abdominal pain, and higher levels of inflammation throughout the body. But most of the research on emulsions has been done in rodents, which are easier to study, Whelan says.
These studies found that when rodents consume certain emulsions — at levels similar to those found in ultra-processed foods — bad gut microbes grow more than good ones, the protective layer of mucus lining the intestines becomes thinner, and intestinal inflammation increases, says Benoit Chassin, a microbiome researcher at the Pasteur Institute in Paris. Chronic bowel inflammation can increase the risk of diseases such as inflammatory bowel disease and colorectal cancer, Chan says.
Researchers also found that when people with Crohn’s disease avoided lozenges, their symptoms improved.
Some rodent studies have indicated that consumption of artificial sweeteners such as sucralose, acesulfame K, and saccharin may lead to an imbalance in the gut microbiome and a more permeable intestinal lining.
There is not enough research to prove whether these sweeteners have the same effects in humans. But in a study of 137 adults published in 2022, researchers found that those who consumed foods and drinks containing the sweeteners every day had worse digestive symptoms, such as diarrhea, constipation, and heartburn, compared to those who avoided them.
What does this mean for you?
There’s still a lot of scientists who don’t understand how ultra-processed foods affect the gut, and there’s not enough evidence to recommend avoiding such products completely, Whelan says.
But we do know that it may be beneficial to reduce consumption, Narula says, as there is good evidence linking ultra-processed foods to other health conditions, such as cardiovascular disease, dementia and obesity.
He recommended thinking about the ultra-processed foods you eat regularly and identifying ways to replace them with unprocessed alternatives, such as drinking sparkling water or iced coffee instead of soda, or making homemade salad dressing instead of using bottled dressing.
For a healthy gut, focus on eating plenty of whole foods rich in fiber, such as fruits and vegetables. Limiting sodium, added sugars and saturated fats is good for your overall health. If you follow this advice, Whelan says, you’ll likely consume fewer ultra-processed foods along the way.