how do ultra processed foods harm your gut health?

Not all foods are created equal, and one group in particular has been getting a lot of attention lately: UPFs, or ultra-processed foods. Around 54% of calories in the average UK adult diet now come from UPFs. So what are they exactly, and why should you care?

What Are Ultra-Processed Foods?

Ultra-processed foods are items that go through lots of industrial processing and often contain ingredients you wouldn’t find in a home kitchen - such as preservatives, emulsifiers, flavourings and artificial sweeteners. They’re made to last longer on shelves and to enhance taste.

Think packaged snacks, fizzy drinks, instant noodles, ready meals, mass-produced bread, and many breakfast cereals.

The term ‘ultra-processed’ comes from the NOVA classification system, which groups foods by the extent of industrial processing rather than their nutrient content. Not every UPF is harmful in moderation, but high overall intake is the issue.

Not all processed food is ultra-processed

This distinction matters. Processing isn’t inherently bad - most foods involve some level of processing, from washing and chopping to canning and freezing. Tinned tomatoes, frozen peas, plain yoghurt, tinned beans and wholemeal bread baked with simple ingredients are all processed, but not ultra-processed.

Why are ultra processed foods bad for you?

Research suggests that eating a lot of UPFs can change the balance of bacteria in your gut and how they work. This shift may set the stage for longer-term issues, starting in the gut but spreading more widely.

Your gut is home to trillions of microbes that support digestion, nutrient absorption and your immune system. When everything is in balance, these microbes produce protective compounds and help keep inflammation in check.

How Do Ultra-Processed Foods Affect the Gut Microbiome?

There are five main ways UPFs influence the gut.

1. They reduce microbial diversity

UPFs are full of additives, preservatives and emulsifiers. Studies show these can upset the balance of gut bacteria, encouraging the growth of strains linked to inflammation while reducing overall diversity. A less diverse microbiome may mean fewer helpful bacteria supporting your gut.

2. They reduce short-chain fatty acid (SCFA) production

Normally, gut microbes break down fibre to produce short-chain fatty acids, these are helpful compounds made when gut bacteria break down fibre, and they help regulate inflammation and protect against disease. Research has found that UPF-heavy diets lower SCFA production, partly because they tend to be low in the fibre that feeds beneficial bacteria.

You can learn more about feeding beneficial gut bacteria in our guide to Why You Need Prebiotics.

3. Emulsifiers may weaken the gut barrier

 A trial showed that people who ate a diet enriched with the emulsifier carboxymethylcellulose (CMC) for two weeks reported more digestive discomfort and ended up with a less diverse gut microbiome than those on an emulsifier-free diet. Animal and lab studies also suggest CMC and polysorbate 80 may also thin the mucus layer that protects the gut lining.

4. Artificial sweeteners may disrupt the microbiome

Many ultra-processed foods contain artificial sweeteners, with sucralose in particular studied for its effects on the gut microbiome. Scientists are still working to understand the long-term effects, but eating a varied diet rich in whole foods remains the best way to support a healthy microbiome.

5. They’re often high in saturated fat

UPFs often contain a lot of added fat to improve flavour and texture. They are often high in saturated fat, which is associated with poorer overall health, including weight, blood sugar and heart health when consumed in excess. Over time this affects more than the gut, increasing the risk of obesity, diabetes and heart disease

How Can You Reduce Ultra-Processed Foods in Your Diet?

In today’s world, it’s almost impossible to avoid ultra-processed foods altogether. From quick snacks to convenience meals, they’re a part of everyday life. The aim is to create balance rather than chase perfection.

• Aim for one whole-food meal a day. Built around vegetables, whole grains, legumes, fish or meat with simple ingredients. Check out our gut health recipes.

• Read labels for short ingredient lists. The longer the list and the more unfamiliar names, the more ultra-processed the food.

• Swap one UPF item a week for a less processed version. For example, plain Greek yoghurt instead of flavoured pots.

• Increase fibre and plant variety. Aiming for around 30 different plant types a week is associated with greater microbial diversity.

• Keep simple snacks easy to grab. Fruit, nuts, hummus and oatcakes.

For inspiration, and to naturally increase beneficial bacteria, explore Fermented Foods: A Powerhouse for Your Gut.

What Can You Do To Support Your Gut?

Reducing ultra-processed foods is only one part of the picture. Supporting the health and resilience of your gut microbiome can also play an important role in maintaining digestive wellbeing. 

One effective way to do this is with a synbiotic which combines probiotics and prebiotics.

Probiotics

Probiotics are live, beneficial microbes that help restore balance in the gut.

Certain strains, such as Lactobacillus rhamnosus and Bifidobacterium longum, have been studied for their ability to reduce gut inflammation, support the gut lining, and increase microbial diversity.

These functions are particularly important when the microbiome has been disrupted by a diet that is lower in fibre and higher in processed ingredients.

Prebiotics

Prebiotics are non-digestible fibres that act as food for probiotics and other beneficial bacteria. One of the best studied is fructooligosaccharides (FOS).

FOS selectively stimulates the growth of good bacteria like Bifidobacteria, boosting their ability to produce short chain fatty acids (SCFAs).

SCFAs play a crucial role in nourishing the cells of the intestinal lining, regulating inflammation, and keeping the gut environment stable.

Our daily synbiotic dual cap is designed to support microbial balance and gut barrier strength. As part of a wider approach - a varied plant-rich diet, less UPF foods, regular movement, good rest and calm stress care - it may help support your gut day to day.

References

Chassaing, B., Compher, C., Bonhomme, B., Liu, Q., Tian, Y., Walters, W., Nessel, L., Delaroque, C., Hao, F., Gershuni, V., Chau, L., Ni, J., Bewtra, M., Albenberg, L., Bretin, A., McKeever, L., Ley, R. E., Patterson, A. D., Wu, G. D., … Lewis, J. D. (2022). Randomized controlled-feeding study of dietary emulsifier carboxymethylcellulose reveals detrimental impacts on the gut microbiota and metabolome. Gastroenterology, 162(3), 743–756. https://doi.org/10.1053/j.gastro.2021.11.006

NHS. (2022). How to get more fibre into your diet. National Health Service. Retrieved May 2026, from https://www.nhs.uk/live-well/eat-well/digestive-health/how-to-get-more-fibre-into-your-diet/

Rauber, F., Chang, K., Vamos, E. P., da Costa Louzada, M. L., Monteiro, C. A., Millett, C., & Levy, R. B. (2025). Identifying the patterns of ultra-processed food consumption and their characteristics in UK adults using the UK National Diet and Nutritional Surveys 2008/09 to 2018/19. European Journal of Nutrition, 64(6), 222. https://doi.org/10.1007/s00394-025-03727-5

Rondinella, D., Raoul, P. C., Valeriani, E., Venturini, I., Cintoni, M., Severino, A., Galli, F. S., Mora, V., Mele, M. C., Cammarota, G., Gasbarrini, A., Rinninella, E., & Ianiro, G. (2025). The detrimental impact of ultra-processed foods on the human gut microbiome and gut barrier. Nutrients, 17(5), 859. https://doi.org/10.3390/nu17050859

Spiller, A. L., da Costa, B. G., Yoshihara, R. N. Y., Nogueira, E. J. Z., Castelhano, N. S., Santos, A., De Freitas, M. B., Magro, D. O., & Sassaki, L. Y. (2025). Ultra-processed foods, gut microbiota, and inflammatory bowel disease: A critical review of emerging evidence. Nutrients, 17(16), 2677. https://doi.org/10.3390/nu17162677

Suez, J., Cohen, Y., Valdés-Mas, R., Mor, U., Dori-Bachash, M., Federici, S., Zmora, N., Leshem, A., Heinemann, M., Linevsky, R., Zur, M., Ben-Zeev Brik, R., Bukimer, A., Eliyahu-Miller, S., Metz, A., Fischbein, R., Sharov, O., Malitsky, S., Itkin, M., … Elinav, E. (2022). Personalized microbiome-driven effects of non-nutritive sweeteners on human glucose tolerance. Cell, 185(18), 3307–3328.e19. https://doi.org/10.1016/j.cell.2022.07.016

World Health Organization. (2023). Use of non-sugar sweeteners: WHO guideline. World Health Organization. https://www.who.int/publications/i/item/9789240073616

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