Ultra-Processed Food and Gut Health

Medically reviewed and written by Dr Zeeshan Afzal (MBBS), Medical Content Lead at Welzo. Last updated: 29 July 2026. Reading time: approximately 14 minutes.

Ultra-processed food now supplies more than half of the calories eaten by the average UK adult. That single fact matters more to your digestive system than almost any supplement you could buy, because the bacteria in your large intestine live on what arrives there — and ultra-processed products are engineered, more than any other food category, to be absorbed high up in the small intestine and to leave very little behind.

This guide explains what the human evidence actually shows about ultra-processed food and the gut: the mechanisms with real trial data behind them, the ones still confined to mice, what UK bodies such as SACN have concluded, and what you can realistically change. If you are new to this area, start with our overview of gut health in the UK and browse the wider Welzo gut health range. For the microbiome fundamentals referenced throughout, see microbiome diversity, short-chain fatty acids, gut barrier function and gut dysbiosis. Where supplementation is discussed later, the products referenced are Welzo probiotics, Akkermansia muciniphila, modified citrus pectin powder, Welzo Ultra Purity Berberine and Welzo Ultra Purity TUDCA.

Ultra-processed products dominate the centre aisles of UK supermarkets. Image: Wikimedia Commons, CC BY-SA 4.0.

Key points at a glance

• Ultra-processed food (UPF) provides roughly 54–57% of daily calories for UK adults and about 66% for UK adolescents.
• The best-evidenced gut mechanism is fibre displacement: UPF crowds out the plant fibre your bacteria ferment into short-chain fatty acids.
• A controlled human feeding trial found the emulsifier carboxymethylcellulose reduced microbiota diversity and faecal short-chain fatty acids in just 11 days.
• A randomised trial in 120 adults found four common non-nutritive sweeteners altered the gut and oral microbiome, with saccharin and sucralose impairing glucose responses.
• A BMJ umbrella review covering nearly 10 million participants linked higher UPF exposure to 32 adverse health outcomes.
• The UK's SACN concluded the associations are concerning but that evidence limitations mean caution is warranted — most human data remain observational.
• You do not need to eliminate UPF. Adding fibre and plant diversity back in is more achievable, and better supported, than perfectionist avoidance.

Table of contents

• What counts as ultra-processed food?
• How much ultra-processed food do UK adults eat?
• How ultra-processed food affects the gut microbiome
• Ultra-processed food and the gut barrier
• Digestive symptoms linked to a high-UPF diet
• Beyond the gut: whole-body consequences
• What the evidence does and does not prove
• How to reduce ultra-processed food realistically
• Supplements that may support gut recovery
• A four-week lower-UPF gut plan
• When to see a GP
• Frequently asked questions
• References

What counts as ultra-processed food?

"Processed" and "ultra-processed" are not the same thing. Tinned tomatoes, frozen peas, plain yoghurt and bagged wholemeal flour are all processed — and all perfectly good for your gut. Ultra-processing is a different category, defined by the NOVA classification developed by Carlos Monteiro's team at the University of São Paulo and now used in most of the research literature.

The NOVA classification explained

How to spot a UPF on a UK label

You do not need the NOVA paper in the supermarket. Two practical rules capture most of it:

1. Look for ingredients you could not buy or use at home. Maltodextrin, soy protein isolate, invert sugar syrup, hydrogenated or interesterified oils, modified starch, mono- and diglycerides of fatty acids, carboxymethylcellulose (E466), polysorbate 80 (E433), flavourings, colourings, emulsifiers, thickeners and non-sugar sweeteners are all markers of ultra-processing.
2. Look at the front-of-pack claims. Heavy marketing — "high protein", "low fat", "gut-friendly", "fortified" — is disproportionately attached to ultra-processed formulations.

A long ingredient list containing substances with no culinary use is the single most reliable signal of ultra-processing. Image: Wikimedia Commons.

Not all ultra-processed foods are equal

This is where a lot of online advice goes wrong. NOVA classifies by processing, not by nutritional quality, so wholemeal supermarket bread, fortified breakfast cereal, baked beans and plant-based milks all land in group 4 alongside cola and crisps. Large European cohort analyses have found the risk signal is concentrated in specific subgroups — particularly sugar-sweetened and artificially sweetened drinks and processed animal products — while breads and cereals have shown neutral or even inverse associations with cardiometabolic outcomes.

The sensible reading: the subtype matters as much as the label. Swapping a fortified wholemeal loaf for nothing at all is not a gut win. Swapping a daily soft drink for water almost certainly is.

How much ultra-processed food do UK adults eat?

The Rauber analysis also showed something important for digestion specifically: as UPF intake rose across the population, dietary fibre content fell while free sugars, saturated fat and sodium rose. Free sugars climbed from 9.9% to 15.4% of total energy between the lowest and highest UPF quintiles. That is the mechanism in one sentence — ultra-processed food does not just add things, it removes things.

How ultra-processed food affects the gut microbiome

The colon houses the densest microbial community in the body, and its fuel supply is dietary fibre. Image: Wikimedia Commons, CC BY 4.0.

Fibre displacement: the biggest single mechanism

Your colonic bacteria are anaerobic fermenters. They need fermentable substrate — resistant starch, inulin, beta-glucans, pectins, polyphenol-bound fibre — and ultra-processed formulations have had most of that stripped out during refining, extrusion and pre-frying. When it does not arrive, two things follow.

First, short-chain fatty acid production falls. Butyrate is the principal fuel for the colonocytes lining your large bowel; acetate and propionate travel further and influence appetite and hepatic metabolism. Read more on short-chain fatty acids and butyrate supplementation.

Second, fibre-degrading species lose ground. Reviews of UPF and the microbiome consistently report lower relative abundance of Faecalibacterium prausnitzii and Akkermansia muciniphila alongside reduced overall diversity, with a shift towards more pro-inflammatory community profiles. Both of those organisms are workhorses: F. prausnitzii is a major butyrate producer, and A. muciniphila is a mucin specialist that helps regulate the mucus layer. See Akkermansia versus conventional probiotics and how to increase gut bacteria diversity.

Practical fixes for this specific mechanism sit here: how to increase fibre, high-fibre foods in the UK, prebiotic foods and resistant starch.

Emulsifiers and the mucus layer

Emulsifiers keep oil and water phases from separating and give ultra-processed products their shelf life and mouthfeel. Animal work first raised the alarm, showing that dietary emulsifiers alter the intestinal microbiota, thin the protective mucus layer and promote low-grade inflammation and metabolic dysregulation in mice.

The important development is that this has now been tested in people. In a double-blind controlled-feeding study, healthy adults ate either an emulsifier-free diet or an identical diet enriched with 15 g per day of carboxymethylcellulose (E466) for 11 days. Compared with controls, CMC consumption modestly increased post-meal abdominal discomfort, perturbed microbiota composition in a way that reduced diversity, and lowered faecal short-chain fatty acids and free amino acids. Two of the participants developed microbiota encroachment into the normally sterile inner mucus layer — a finding a follow-up analysis interpreted as evidence that individual susceptibility varies substantially.

Two caveats deserve stating plainly. The trial was small (16 participants) and short. And 15 g/day is a high, though not implausible, exposure. But it is human, randomised and controlled — which puts emulsifiers on firmer ground than most proposed UPF mechanisms. If gut barrier integrity is your concern, see gut barrier function and is leaky gut real?.

Non-nutritive sweeteners

Sweeteners were long assumed to be metabolically inert because they pass through undigested. That assumption is what makes them interesting to microbiologists — undigested means they reach the colon intact.

In a randomised controlled trial of 120 healthy adults who were naive to sweetener use, participants took saccharin, sucralose, aspartame or stevia sachets for two weeks at doses below the acceptable daily intake, against two control arms. Each of the four sweeteners distinctly altered the stool and oral microbiome and the plasma metabolome. Saccharin and sucralose significantly impaired glycaemic responses. Transferring the participants' microbiomes into germ-free mice reproduced the glycaemic effects, which is strong evidence that the microbiome was mediating the change rather than merely accompanying it.

This does not mean sweeteners are worse than sugar, and it does not mean everyone responds the same way — responses were highly individual. It does mean "zero calorie" is not the same as "zero effect on the gut". More detail: sweeteners and gut health.

Other additives, thickeners and preservatives

Beyond emulsifiers and sweeteners, ultra-processed products carry preservatives, antimicrobials, colourings and thickening agents. The honest position is that human evidence for most of these is thin. Mechanistic and animal data suggest some antimicrobial preservatives may exert selection pressure on gut bacteria, and regulators have acted on individual additives when evidence warranted — but extrapolating from cell culture or rodent studies to your breakfast is not justified. Treat additive exposure as a reasonable thing to reduce, not a proven cause of your symptoms.

Eating speed and the loss of the food matrix

Ultra-processing physically dismantles food structure. Grains are milled to flour and extruded; cell walls that would normally slow enzymatic access are destroyed. The result is often described as "pre-digested": nutrients are absorbed rapidly and high in the small intestine, so less substrate reaches the colon and glucose enters the bloodstream faster.

The landmark evidence here is Kevin Hall's inpatient randomised controlled trial at the NIH. Twenty weight-stable adults ate an ultra-processed diet and a matched unprocessed diet for two weeks each, with meals matched for presented calories, sugar, fat, sodium, fibre and macronutrients. On the ultra-processed diet, participants ate roughly 500 kcal/day more, ate faster, and gained 0.9 kg; on the unprocessed diet they lost 0.9 kg. Matching the nutrients did not neutralise the effect of the processing itself.

Related reading: gut health and blood sugar and gut health and weight loss.

What happens to short-chain fatty acids

Ultra-processed food and the gut barrier

The intestinal barrier is not one thing. It is a mucus layer, an epithelial cell sheet joined by tight junctions, and an immune apparatus sitting immediately beneath. Reviews of UPF and gut health propose that the combination of low fibre, emulsifier exposure and reduced SCFA production degrades all three: less butyrate means less fuel for colonocytes and weaker tight-junction signalling, a thinner mucus layer means bacteria sit closer to the epithelium, and the result is chronic low-grade inflammation.

This is biologically coherent and supported by animal work. In humans it remains a plausible mechanism rather than a demonstrated chain of causation — which is why we would caution against anyone selling you a "leaky gut cure". Our balanced assessment sits at is leaky gut real?, with testing covered at zonulin testing and supplement options at best supplements for leaky gut.

Digestive symptoms linked to a high-UPF diet

Bloating and trapped wind

A high-UPF diet can produce bloating through several routes at once: sugar alcohols and polyols in "sugar-free" products, carbonation, rapid eating and air swallowing, and the fermentation shifts described above. Confusingly, increasing fibre too quickly also causes bloating — which is why people often conclude fibre is the problem when the pace of change was the problem. See foods that cause bloating, trapped wind relief and supplements for bloating.

Constipation and stool form

Low fibre intake reduces stool bulk and water-holding capacity, and a diet built on UPF is almost by definition a low-fibre diet. Stool form is the most useful self-monitoring tool you have — check yours against the Bristol stool chart, and see constipation relief and magnesium for constipation.

Irritable bowel syndrome

IBS is a diagnosis of specific criteria, not a synonym for a sensitive stomach. UPF reduction is not a validated IBS treatment, and for some people fermentable fibres worsen symptoms in the short term — which is why the low FODMAP approach exists as a structured, time-limited tool. See IBS types, the low FODMAP diet, FODMAP reintroduction and supplements for IBS.

Inflammatory bowel disease

The PURE study followed 116,087 adults across 21 countries and found that higher ultra-processed food intake was associated with a higher risk of developing inflammatory bowel disease, while intake of individual food categories such as meat, dairy and starch was not. Separate analyses in three large US health-professional cohorts found higher UPF intake associated with increased risk of Crohn's disease specifically.

These are observational findings and cannot establish cause. But the pattern — risk tracking with processing rather than with any particular macronutrient — is what makes researchers suspect additives and the food matrix rather than fat or protein content. If you live with IBD, see Crohn's disease diet and ulcerative colitis diet, and discuss dietary changes with your IBD team before making them.

Beyond the gut: whole-body consequences

The 2024 BMJ umbrella review by Lane and colleagues pooled 45 unique analyses covering 9,888,373 participants. Higher UPF exposure was directly associated with 32 of the 45 health parameters assessed (71%), spanning mortality, cancer, and mental, respiratory, cardiovascular, gastrointestinal and metabolic outcomes.

The gut is plausibly one route by which several of these arise. Microbial metabolites influence immune signalling, appetite regulation, bile acid handling and vagal signalling to the brain. That territory is covered in the gut-brain connection, probiotics for anxiety, gut health and the immune system, the vagus nerve and the gut, and gut health and sleep.

What the evidence does and does not prove

This section matters, and most articles on this topic skip it.

In July 2023 the UK's Scientific Advisory Committee on Nutrition published a position statement on processed foods and health. Its conclusions were carefully worded: NOVA was the only classification system meeting SACN's screening criteria for UK use, but SACN identified practical problems applying it to National Diet and Nutrition Survey data, and noted that some NOVA classifications conflict with existing UK dietary advice. SACN concluded that the association between higher UPF consumption and adverse health outcomes is concerning, but that limitations in the evidence — which is overwhelmingly observational — meant it was unclear whether these foods are harmful because of processing itself or because most of them are high in energy, saturated fat, salt and free sugars. SACN's rapid evidence update in April 2025 reviewed newer publications and maintained a cautious stance.

In November 2025, a three-paper Lancet Series took a firmer view, arguing that ultra-processed foods are displacing fresh and minimally processed foods worldwide, that this worsens diet quality and is associated with multiple chronic diseases, and that the current science is already sufficient to justify policy action. Both positions can be held honestly: the observational evidence is consistent and large, and the causal evidence — outside of weight gain, where Hall's trial is decisive — remains limited.

What this means for you: reducing ultra-processed food is a low-risk, plausibly high-benefit change. It is not a treatment for a diagnosed condition, and it should not delay investigation of persistent symptoms.

How to reduce ultra-processed food realistically

Plant diversity — not perfection — is the target that matters most for the microbiome. Image: Wikimedia Commons.

Step 1: Audit before you change anything

Spend three days writing down everything you eat without changing it. Then mark every item that contains an ingredient you could not buy in a normal shop. Most people find their UPF intake is concentrated in two or three predictable places — usually breakfast, the afternoon snack and drinks — rather than spread evenly. Fixing those is a far better use of effort than reading every label in the supermarket.

Step 2: Swap the highest-frequency items first

Step 3: Add before you subtract

Subtraction diets fail. Addition targets work better because they are measurable and non-punitive. The two worth using are the 30 plants a week target — herbs, spices, nuts, seeds, wholegrains and pulses all count — and a gradual fibre ramp towards 30 g/day, increasing by roughly 5 g per week with fluid alongside. Detailed guidance sits at how to increase fibre and best foods for gut health.

Thirty different plants a week is more achievable than it sounds once herbs, spices, nuts and pulses are counted. Image: Wikimedia Commons, CC BY-SA 4.0.

Step 4: Include fermented foods

Fermented foods sit in NOVA group 3 when made traditionally and are a straightforward way to add microbial and metabolite diversity. Live yoghurt, kefir, sauerkraut, kimchi, miso and traditional cheeses all qualify — check that supermarket versions have not been pasteurised after fermentation or bulked out with thickeners. See fermented foods in the UK, kefir benefits and fermented food versus probiotics.

Step 5: Be honest about cost, time and access

Ultra-processed food is cheap, shelf-stable and requires no equipment or skill, and telling people to simply avoid it ignores real constraints. Frozen and tinned vegetables, dried pulses, oats and own-brand nuts are among the cheapest sources of fibre per gram in any UK supermarket. If your budget is tight, prioritise fibre volume over organic status or trendy formats — the bacteria cannot tell the difference.

Supplements that may support gut recovery

Supplements do not offset a high-UPF diet. No probiotic replaces fibre, and any product marketed on that promise is misrepresenting the evidence. What supplements can reasonably do is support a transition, or address a specific deficit. The options below are listed with a candid assessment of evidence strength.

Probiotics

Evidence for probiotics is strain-specific rather than category-wide, and strongest for defined indications such as antibiotic-associated diarrhoea rather than for general "gut repair". If you are considering one, start with how to choose a probiotic, the best probiotics in the UK and do probiotics work?. Browse the Welzo probiotics collection. Timing and expectations: when to take probiotics and how long probiotics take to work.

Prebiotics and fibre supplements

A fibre supplement is a reasonable bridge while food intake improves, though it is not a substitute for dietary variety — a single isolated fibre feeds a narrower range of bacteria than thirty plants do. See best prebiotic supplements, psyllium versus inulin and prebiotic versus probiotic.

Akkermansia muciniphila

Because A. muciniphila is among the species reported at lower abundance in high-UPF dietary patterns, direct supplementation has attracted interest. Human trial data are early-stage and mostly metabolic rather than gastrointestinal. See Welzo Akkermansia, pasteurised Akkermansia and how it compares to standard probiotics.

Polyphenols and pectin

Polyphenols reach the colon largely unabsorbed and are metabolised by gut bacteria — one of the more interesting overlaps between diet and the microbiome. See polyphenols and gut health, citrus pectin powder, modified citrus pectin versus standard pectin and our PectaSol review.

Metabolic and bile-related options

Because high-UPF diets track with glycaemic and metabolic disturbance, some people ask about berberine and TUDCA. Both have specific, limited evidence bases and meaningful interaction profiles. Berberine has notable drug interactions — read berberine interactions and berberine versus metformin first. TUDCA relates to bile acid handling; see TUDCA side effects and bile acid malabsorption. Neither is appropriate without considering your medications and medical history, and neither should be started in place of seeking a diagnosis.

What supplements cannot do

• They cannot replace fermentable fibre from a varied diet.
• They cannot "detox" additives already consumed.
• They cannot diagnose the cause of persistent digestive symptoms.
• They can interact with prescribed medication — check before starting, particularly if you take anticoagulants, diabetes medication or immunosuppressants.

A four-week lower-UPF gut plan

Expect some wind and looser stools in weeks 2 to 3 as fermentation increases. This usually settles within one to two weeks. If it does not, slow the rate of increase rather than abandoning the change. See our gut reset protocol for a longer structured version.

When to see a GP

Dietary change is not the right first response to every symptom. Arrange a GP appointment promptly if you have:

• Blood in your stool, or black tarry stools
• Unintentional weight loss
• A persistent change in bowel habit lasting more than three weeks, particularly if you are over 50
• Difficulty swallowing, or persistent vomiting
• Iron deficiency anaemia without an obvious cause
• A family history of bowel cancer, coeliac disease or inflammatory bowel disease alongside new symptoms
• Persistent abdominal pain that wakes you at night

More detail: when to see a GP about stomach symptoms, bowel cancer screening in the UK, coeliac testing and faecal calprotectin testing. If you want to characterise your microbiome, see gut microbiome testing in the UK — with the caveat that these tests are not diagnostic.

Frequently asked questions

Does ultra-processed food damage your gut?

High ultra-processed food intake is consistently associated with reduced gut microbiome diversity, lower levels of beneficial fibre-fermenting bacteria such as Faecalibacterium prausnitzii and Akkermansia muciniphila, and reduced short-chain fatty acid production. Human trials have shown that a common emulsifier reduced microbiota diversity and faecal short-chain fatty acids within 11 days. However, most evidence in people is observational, and the UK's SACN has concluded that it is not yet clear whether processing itself is harmful or whether the harm comes from the typical nutrient profile of these foods.

How long does it take the gut microbiome to recover after cutting ultra-processed food?

Microbiome composition begins shifting within days of a substantial dietary change, and measurable increases in short-chain fatty acid production can follow within one to two weeks of increased fibre intake. More durable changes in diversity typically take weeks to months, and some species do not return without being reintroduced. Digestive symptoms such as bloating often worsen briefly in the first one to two weeks before improving.

Is all processed food bad for gut health?

No. Tinned pulses, frozen vegetables, plain yoghurt, wholemeal flour, olive oil and traditionally fermented foods are all processed and are among the better things you can eat for your gut. The specific concern is NOVA group 4 — industrial formulations containing substances of no culinary use plus cosmetic additives. Even within that group, the risk signal is stronger for soft drinks and processed meats than for items such as wholemeal bread and fortified cereals.

Do emulsifiers in food really harm gut bacteria?

In a double-blind controlled feeding trial, healthy adults consuming 15 g per day of carboxymethylcellulose for 11 days showed reduced microbiota diversity, reduced faecal short-chain fatty acids and modestly increased post-meal abdominal discomfort compared with controls, with two participants developing bacterial encroachment into the mucus layer. This is a small, short study at a high dose, and responses varied substantially between individuals — so it demonstrates a real effect in some people rather than a universal harm.

Are artificial sweeteners bad for the gut microbiome?

A randomised trial in 120 healthy adults found that saccharin, sucralose, aspartame and stevia each altered the stool and oral microbiome over two weeks at doses below the acceptable daily intake, and that saccharin and sucralose impaired glycaemic responses. Transplanting participants' microbiomes into germ-free mice reproduced the glycaemic effects. Responses were highly individual, and this does not establish that sweeteners are worse than the sugar they replace.

What percentage of the UK diet is ultra-processed food?

Analyses of the National Diet and Nutrition Survey put ultra-processed food at approximately 54–57% of daily energy intake for UK adults and around 66% for adolescents aged 11 to 18. The UK has among the highest UPF intakes internationally, alongside the United States.

Can probiotics undo the effects of ultra-processed food?

No. Probiotics are transient in most people and do not replace the fermentable fibre that resident gut bacteria depend on. Specific strains have evidence for specific indications, but no probiotic has been shown to offset a high-UPF dietary pattern. Increasing plant diversity and fibre intake is the intervention with the strongest supporting evidence.

Does ultra-processed food cause IBS or IBD?

Causation has not been established for either. In the PURE study of 116,087 adults across 21 countries, higher ultra-processed food intake was associated with a higher risk of developing inflammatory bowel disease, and US cohort studies found a similar association with Crohn's disease. These are observational findings. For IBS, no trial has shown that UPF reduction treats the condition, and some people with IBS find fermentable fibres worsen symptoms initially.

What are the first signs that ultra-processed food is affecting your gut?

The most common early indicators are changes in stool form and frequency — typically harder, less frequent stools reflecting low fibre intake — along with bloating, wind, and reduced satiety leading to more frequent snacking. None of these is specific to UPF, so persistent symptoms warrant assessment rather than self-diagnosis.

How much ultra-processed food is acceptable?

There is no official UK threshold, and SACN has not set one. Cohort data show dose-response relationships, meaning benefit tends to scale with reduction rather than requiring elimination. A practical approach is to reduce the highest-frequency items — daily soft drinks, snacks and breakfast products — while keeping convenient, fortified or affordable UPF items where they are genuinely useful.

References

1. Monteiro CA, Cannon G, Levy RB, et al. Ultra-processed foods: what they are and how to identify them. Public Health Nutrition. 2019;22(5):936–941.
2. Rauber F, da Costa Louzada ML, Steele EM, et al. Ultra-processed food consumption and chronic non-communicable diseases-related dietary nutrient profile in the UK (2008–2014). Nutrients. 2018;10(5):587.
3. Hall KD, Ayuketah A, Brychta R, et al. Ultra-processed diets cause excess calorie intake and weight gain: an inpatient randomized controlled trial of ad libitum food intake. Cell Metabolism. 2019;30(1):67–77.
4. NIH Clinical Center. First randomized, controlled study finds ultra-processed diet leads to weight gain. 2019.
5. Chassaing B, Compher C, Bonhomme B, et al. Randomized controlled-feeding study of dietary emulsifier carboxymethylcellulose reveals detrimental impacts on the gut microbiota and metabolome. Gastroenterology. 2022;162(3):743–756.
6. Chassaing B, et al. Human intestinal microbiome determines individualized inflammatory response to dietary emulsifier carboxymethylcellulose consumption. Cellular and Molecular Gastroenterology and Hepatology. 2023.
7. Suez J, Cohen Y, Valdés-Mas R, et al. Personalized microbiome-driven effects of non-nutritive sweeteners on human glucose tolerance. Cell. 2022;185(18):3307–3328.
8. Lane MM, Gamage E, Du S, et al. Ultra-processed food exposure and adverse health outcomes: umbrella review of epidemiological meta-analyses. BMJ. 2024;384:e077310.
9. Narula N, Wong ECL, Dehghan M, et al. Association of ultra-processed food intake with risk of inflammatory bowel disease: prospective cohort study. BMJ. 2021;374:n1554.
10. Rondinella D, Raoul PC, Valeriani E, et al. The detrimental impact of ultra-processed foods on the human gut microbiome and gut barrier. Nutrients. 2025;17(5):859.
11. Brichacek AL, Florkowski M, Abiona E, Frank KM. Ultra-processed foods: a narrative review of the impact on the human gut microbiome and variations in classification methods. Nutrients. 2024;16(11):1738.
12. Scientific Advisory Committee on Nutrition. SACN statement on processed foods and health. GOV.UK, July 2023.
13. Scientific Advisory Committee on Nutrition. Processed foods and health: SACN's rapid evidence update summary. GOV.UK, April 2025.
14. Cordova R, Viallon V, Fontvieille E, et al. Consumption of ultra-processed foods and risk of multimorbidity of cancer and cardiometabolic diseases: a multinational cohort study. The Lancet Regional Health – Europe. 2023;35:100771.
15. Chen Z, Khandpur N, Desjardins C, et al. Ultra-processed food consumption and risk of type 2 diabetes: three large prospective U.S. cohort studies. Diabetes Care. 2023;46(7):1335–1344.
16. The Lancet. Series: Ultra-processed foods and human health. November 2025.
17. NHS. How to get more fibre into your diet.
18. Guts UK. Fibre.
19. British Dietetic Association. Fibre food fact sheet.
20. Communications Biology. Common dietary emulsifiers promote metabolic disorders and intestinal microbiota dysbiosis in mice. 2024.

About the author

Dr Zeeshan Afzal (MBBS) is a practising doctor and Medical Content Lead at Welzo, where he writes and reviews clinical content across digestive health, longevity and preventive medicine. He has a particular interest in translating microbiome research into advice that holds up in ordinary NHS practice — including being clear about where the evidence stops.

Editorial standards. Welzo articles cite primary research, peer-reviewed reviews and UK public health sources wherever possible. Statistics in this article were checked against their original publications. Content is reviewed at least every 12 months, or sooner when significant new evidence is published.

Medical disclaimer

This article is for general information and does not constitute medical advice, diagnosis or treatment. It should not replace consultation with your GP, pharmacist or a registered dietitian. Do not start, stop or change any supplement or medication on the basis of this article, particularly if you are pregnant or breastfeeding, take prescription medicines, have a diagnosed gastrointestinal or immune condition, or are immunocompromised. If you have concerning digestive symptoms, contact your GP or NHS 111. In an emergency, call 999.

Related reading from Welzo

• Gut health in the UK: complete guide
• Best foods for gut health
• Microbiome diversity explained
• The 30 plants a week target
• Sweeteners and gut health
• Gut dysbiosis: causes and signs
• The gut reset protocol
• Shop gut health at Welzo