Worst Foods for Gut Health: 10 Ingredients That Disrupt Your Microbiome

When people talk about gut health, the focus usually lands on what to add: more fiber, more fermented foods, more plants. That’s important, but it’s only half the picture. Just as certain foods support the microbiome, others can quietly work against it. A fuller understanding of the worst foods for gut health helps explain why digestion, energy, and immune resilience can feel off, even when you’re trying to eat “well.”

Still, rather than demonizing entire food groups, it’s more helpful to look at patterns. Many of the foods that disrupt the gut do so by reducing microbial diversity, affecting the gut lining, or interfering with how bacteria metabolize nutrients. Over time, those effects can compound.

What are the 10 worst foods for gut health?

The foods below aren’t necessarily harmful in moderation, but they’re consistently associated with negative shifts in the microbiome when consumed frequently.

1. Refined sugars
High intakes of added sugar encourage the growth of less beneficial bacteria while crowding out fiber-fermenting species. Diets high in refined sugar are linked to reduced microbial diversity and may affect immune health in the gut.¹

2. Ultra-processed foods
Packaged foods often combine refined carbohydrates, additives, and low fiber content—none of which are ideal. Regular consumption of ultra-processed foods is associated with poorer gut barrier function and unfavorable microbiome changes².

3. Artificial sweeteners
Non-nutritive sweeteners such as saccharin and sucralose may alter gut bacteria in ways that affect glucose metabolism and microbial balance, even without the added calories³.

4. Emulsifiers
Common emulsifiers like polysorbate-80 and carboxymethylcellulose—found in ice cream and processed sauces—have been shown to disrupt the gut lining and may affect gut barrier integrity in animal and human studies. ⁴

5. Refined grains
White bread, pastries, and refined cereals lack the fibers that feed beneficial bacteria. Diets dominated by refined grains are linked to lower microbial diversity compared to whole-grain diets⁵.

6. Processed meats
Processed meats contain additives and saturated fats that have been associated with unfavorable gut responses and changes in bile-tolerant bacteria linked to colon health.

7. Fried foods
Deep-fried foods are high in oxidized fats that can affect the gut lining and negatively affect microbial composition⁸.

8. Industrial seed oils (in excess)
Highly refined oils consumed excessively, especially without balancing omega-3 intake, may negatively affect the gut environment. ⁹

9. Highly salted foods
Very high sodium intake has been shown to reduce beneficial Lactobacillus populations and may affect immune health. ¹⁰

How these foods harm digestion

Digestion relies on collaboration between the gut lining, digestive enzymes, and microbes. Many of the foods that are not ideal for the gut directly interfere with that relationship running smoothly.

Low-fiber, high-sugar foods starve fiber-fermenting bacteria that produce short-chain fatty acids—compounds that help maintain the integrity of your gut lining. Additives and emulsifiers can directly thin the mucus layer that protects the intestinal wall. Over time, these disruptions may lead to bloating, irregular bowel movements, or reduced nutrient absorption¹¹.

Foods that can negatively affect colon health

Your colon depends heavily on microbial fermentation. Diets low in fermentable fiber and high in processed foods reduce the production of butyrate, a short-chain fatty acid that supports colon cells.

Processed meats, refined grains, and low-fiber diets are frequently cited among the worst foods for colon health due to their association with unfavorable microbial metabolites¹².

On the other hand, diets that are rich in diverse plant fibers support colon health by fueling beneficial bacteria and maintaining a healthy gut environment—a big reason why discussions of the best and worst foods for gut health almost always come back to the subject of fiber diversity.

A more supportive way forward

Again, understanding the “worst” foods for your gut isn’t wholly about restriction for its own sake. It’s more about recognizing which patterns make it harder for the microbiome to do its job.

Supporting gut health means reducing your reliance on highly processed foods while increasing fiber-rich plants, fermented foods with live cultures, and nutrients that support digestion and microbial balance. Over time, these choices help restore diversity and resilience in the gut’s ecosystem.

Gut health is shaped by what you do most days, not by single meals or short-term changes. When the baseline improves through intentional, daily habits, like drinking AG1 each day. digestion, energy, and overall well-being often follow.*

References:

1. Chassaing B, Gewirtz AT. Diet, gut microbiota, and metabolic health. Front Immunol. 2017;8:548. doi:10.3389/fimmu.2017.00548
2. Srour B, Fezeu LK, Kesse-Guyot E, et al. Ultra-processed food intake…: prospective cohort study (NutriNet-Santé). BMJ. 2019;365:l1451. doi:10.1136/bmj.l1451
3. Suez J, Korem T, Zeevi D, et al. Artificial sweeteners induce … by altering the gut microbiota. Nature. 2014;514(7521):181–186. doi:10.1038/nature13793
4. Chassaing B, Koren O, Goodrich JK, et al. Dietary emulsifiers impact the gut microbiota…. Nature. 2015;519(7541):92–96. doi:10.1038/nature14232
5. Martínez I, Lattimer JM, Hubach KL, et al. Gut microbiome composition is linked to whole-grain–induced immunological improvements. ISME J. 2013;7(2):269–280. doi:10.1038/ismej.2012.104
6. Bishehsari F, Magno E, Swanson G, et al. Alcohol and gut-derived…. Alcohol Res. 2017;38(2):163–171.
7. Devkota S, Wang Y, Musch MW, et al. Dietary-fat–induced taurocholic acid promotes …. Nature. 2012;487(7405):104–108. doi:10.1038/nature11225
8. Zinöcker MK, Lindseth IA. The Western diet–microbiome-host interaction and its role …. Nutrients. 2018;10(3):365. doi:10.3390/nu10030365
9. Simopoulos AP. The importance of the omega-6/omega-3 fatty acid ratio…. Exp Biol Med (Maywood). 2008;233(6):674–688. doi:10.3181/0711-MR-311
10. Wilck N, Matus MG, Kearney SM, et al. Salt-responsive gut commensal modulates TH17 axis…. Nature. 2017;551(7682):585–589. doi:10.1038/nature24628
11. Chassaing B, Van de Wiele T, De Bodt J, et al. Dietary emulsifiers directly alter human microbiota composition and gene expression ex vivo potentiating intestinal inflammation. Cell Host Microbe. 2017;21(4):426–436.e5. doi:10.1016/j.chom.2017.02.005
12. Song M, Chan AT, Sun J. Influence of the gut microbiome, diet, and environment on ... . Gastroenterology. 2020;158(2):322–340. doi:10.1053/j.gastro.2019.06.048
13. Rohr MW, Narasimhulu CA, Rudeski-Rohr TA, Parthasarathy S. Negative effects of a high-fat diet on intestinal permeability: a review. Adv Nutr. 2020;11(1):77–91. doi:10.1093/advances/nmz061