The Role of Food in UC
For licensed medicines, randomised, placebo-controlled trials are performed to prove that the drug works. As quality of scientific evidence goes, this is the "gold standard", but unfortunately such trials are rarely carried out to determine the impact of diet on ulcerative colitis (UC) because 1) randomised trials are very expensive, often running into the tens of millions of dollars, and 2) it is extremely difficult to run such trials for diet, as changing a single variable between trial arms is impractical and it is challenging to verify that patients are not cheating.
Nevertheless, there have been some randomised, controlled food trials carried out in UC. One which was of particular interest to the author was published in 2022 in the BMJ (here). It involved 66 patients with active UC being administered either faecal transplant + an anti-inflammatory diet, or optimised standard medical therapy. At 8 weeks, those who received the former reported a higher rate of clinical response (66% vs 36%), remission (60% vs 32%) and deep remission (36% vs 9%), with all differences being statistically significant. Fascinatingly, the anti-inflammatory diet was far superior to standard medical therapy at maintaining deep remission until 48 weeks (25% vs 0%, statistical significance was reached, p=0.007). It is clear from this study, and many others, that diet really does have the potential to improve UC's disease course, in the author's view, but the big question is, what is an optimised diet for UC?
The answer to that likely lies in the vast array of epidemiological studies, which look at the incidence of UC in different groups of people with different diets. Epidemiological studies are considered a lower form of evidence when compared to randomised clinical trials, but they are still useful, especially if the signals found in the data are very strong. For example, it was epidemiological studies that discovered the link between smoking and lung cancer (here), and no one disputes this link today. On this page, we consider dozens if not hundreds of scientific studies in an attempt to formulate an optimal diet for UC sufferers.
The advice given below is split into two -
We also examine the Case For Dairy, The Role of Sulphur, What Cooking Oil to Use, The Case For Organic Food and A Note on Veganism.
An important note before we get started - these diets are designed to be followed when in remission from UC with the hope of extending that remission. Many of the recommended foods are likely to be painful to eat when there is active inflammation in the colon due to their high fibre content. Therefore, when disease is active (i.e. when flaring), the author recommends to eat none of the "Foods to avoid" and eat as many of the "Foods to include" as you can tolerate. As the flare diminishes, you can add in more positive foods. It is also worth noting that many of the recommended foods can be consumed in forms which are easier to tolerate; for example, they can be blended, or juiced. As symptoms improve, you should strive towards eating them in their whole forms, with skin on if possible.
It is important to manage your expectations - do not expect instant results. It is likely that dietary changes exert positive and negative effects on UC through their modulation of the gut microbiome, which takes time. Data shows that it takes certainly several months, and possibly years for gut microbes to fully recover following a single course of antibiotics (here and here) so you should be thinking on a timeframe of months (and years), not weeks or days. With that said, let's take a look at a high-level summary of foods to avoid and foods to add to your daily diet, in the table below. A more detailed discussion of each recommendation follows.
Summary of Recommendations
Foods to Avoid - Strong Evidence
Confectionery
This category includes all sweets, biscuits, chocolate bars, cookies, cakes, ice cream and anything else that is high in sugar and fat and contains numerous additives to bring it all together. The evidence is clear, in the author's view, that a high consumption of confectionery is associated with a higher risk of developing UC. One study (here) of 116k adults globally found that those who ate >100 grams a day of sweets had a 208% increased risk of developing UC, compared to those who ate none, keeping all other factors constant. Another study (here) of 111 UC patients in Japan matched UC patients to healthy controls and found that sweets consumption was associated with a 186% increase in risk of developing UC, when comparing the quarter of patients who ate the most sweets vs the quarter who ate the least.
In the author's view, people with UC should never eat confectionery and there are compelling reasons to believe that these foods in particular are very harmful. Confectionery is high in sugar and fat and usually has a large quantity of additives, including emulsifiers, which are known to be risky ingredients for UC sufferers (see below, on ultra-processed foods, for more explanation and evidence). It is likely the combination of these additives with sugar that makes this type of food so bad for UC. Please see the section below on Sugar for a discussion of how this ingredient is likely harmful for UC sufferers.
What alternatives can I eat?
While it is best to eschew confectionery altogether, the author acknowledges that some people really can't do without it. If this applies to you, then very dark chocolate is likely ok for an occasional treat (check the ingredients to ensure it only contains cacao and sugar, with no additives), but even better than that would be fruit or nuts, which are likely beneficial. You can also make your own puddings from simple ingredients, such as cacao, butter, flour, eggs and sugar (limited), which covers most cakes/puddings.
Ultra-Processed Foods
Ultra-processed foods (UPFs) can be defined as food that is made by a series of industrial processes, that contains little or no whole foods and contains ingredients that you would not find in a household kitchen, including most additives such as emulsifiers, stabilisers, artificial sweeteners and preservatives (here). These foods are typically sold in supermarkets in the form of packets, jars, sachets or boxes and do not usually require much preparation before being eaten. This convenience has driven consumption of UPFs from ~0% of the UK's diet in the 1950s, to ~54% in 2017 (here) and to ~57% in the US (here).
Evidence from epidemiology studies is clear that UPFs are strongly associated with a higher risk for UC. The PURE study (here) followed the diets of 116k participants from 21 countries across 9.7 years of follow-up, during which time 377 developed UC. It found that >5 servings of UFPs per day resulted in an 82% higher risk of developing IBD and this fell to 67% with 1-4 servings per day, compared with <1 serving. The p-value for this trend was 0.006, indicating it was highly statistically significant. It is also worth noting that each subgroup of UPFs (soft drinks, refined sweetened food, salty snacks and processed meat) were also independently associated with higher risk of IBD. Cutting the data to only include the risk of developing UC (not Crohn's), the increase in risk is 46% for >5 servings of UFPs per day and 54% for 1-4/day. This study (here) using the same data found that the risk of UC increased by 57% in those who ate >100 grams of UPFs/day vs those who ate none (keeping other factors constant) and that this was statistically significant.
The author strongly recommends that you cut out UPFs, perhaps saving them for very occasional treats. In particular, one emulsifier that several studies have linked to UC is carrageenan (here), and maltodextrin is also suspect (here). A clinical trial found the addition of carrageenan to the diets of UC patients (here) led to relapses in 3/6 patients vs 0/6 in those who received placebo; moreover in those who received carrageenan, both interlekin-6 and faecal calprotectin (biomarkers for inflammation severity) were higher vs placebo and this was statistically significant. There is strong evidence that food additives modify the gut microbiome in a negative way (here and here). Fast food may or may not contain additives, but it is almost always high in fat and sugar and nutritionally empty (i.e. it contains few vitamins, minerals or fibre) and the author recommends you do not eat it. This Swedish study (here) found that fast food intake of twice or more per week increased the risk of developing UC by 290%.
Processed Meats
A meat is processed if it has been modified (e.g. chemically, smoked, cured) in some way to change the taste or extend its life. This category includes bacon, salami, other spicy sausages, hot dogs, canned meat and others. This study (here) in 116k adults globally found that eating over 1 serving of processed meat per day was associated with a 119% increase in risk of developing UC, when compared to those eating no processed meat. Most studies the author has read do not differentiate between red meat and processed meat (which is an error, in the author's view). However, this same study did differentiate, and showed that consumption of unprocessed red meat had no impact on development of IBD (even with >7 servings/week) and there was also no statistical impact of unprocessed white meat consumption on UC risk. This study (here) on 191 UC patients in remission, found that relapse of UC was associated with eating meat (~3x higher risk in top third of meat eaters vs bottom third), with a ~5x higher risk among "red and processed meats". Studies have consistently found a link between UC and high meat intake, but in the author's view it is likely that most of this risk is being driven by processed meat, which usually has the highest risk (when it is a separate category), as well as high meat consumption resulting in lower veg/fruit consumption, which are likely UC-protective. The author therefore recommends to cut out processed meats entirely, but unprocessed red and white meat may be enjoyed in moderation, provided they are served alongside a good variety of vegetables.
Foods to Avoid - Weaker Evidence
High Sugar
By sugar, we are talking about added, refined sugar, not natural sugars that are already contained in a whole food (e.g. fruit). The difference between the two is that natural sugars in fruit are packaged up in layers of fibre, which means they are processed very differently by the body, whereas refined sugar has had all fibre and other components (protein, fat, complex carbohydrates) stripped away. Refined sugar is often added to UPFs and is found in high amounts in confectionery and fast food, which we have already covered.
Reviewing the literature, we find that refined sugar as a single ingredient is generally, though not always, associated with UC. This meta-study (here) combined 4 cohort studies to test for associations between sugar intake and UC, finding that there was a statistically significant positive correlation between the two (59% higher risk of UC with high sugar consumption). This is further supported by a Danish study from 2011, which found high sugar intake (defined as any two of sugar in tea, coffee, breakfast or soft drinks) was the largest risk factor for developing UC, with a 68% higher risk (here). This study (here) found a 10% increase in risk of developing UC with each 10g more of sucrose (table sugar) eaten per day.
It is clear in the author's view that there is reasonable evidence for sugar being implicated in UC development and that therefore it should be consumed in moderation (once per week or less). Natural sugar consumed as part of fruit appears to be fine, as shown by the same study quoted from above (here), which detected a 44% lower risk of developing UC if one fruit were eaten per day.
High Protein
Several studies have found a link between UC and high consumption of protein. Protein is, of course, an essential macronutrient that everyone needs to eat, but it appears that eating much more than your body needs may be harmful for UC. A 2010 study (here) of 68k participants found a 230% increased risk of UC among the top third consumers of protein vs the bottom third. It also found that animal protein was more associated with UC than total protein, with protein from meat and fish being associated with UC, but not protein from eggs and dairy. Other studies have confirmed that high consumption of meat and fish may be associated with UC (here and here). Amongst 191 UC patients in remission, this study (here) found that the top third protein consumers were 3x more likely to relapse than the bottom third.
Clearly, high protein as a category overlaps with processed meats and UPFs, so it is unclear where exactly the risk is coming from, but some studies have suggested that unprocessed red and white meats do not add to UC risk (e.g. here). It could also be that it is the high sulphur content in protein which is the driver of the higher risk (see Sulphur section). Regardless, it is important to note that simple changes to your diet could help across multiple categories and the author's advice here is to not overeat high-protein foods, especially meat and certainly not of the processed kind.
Foods to Eat - Strong Evidence
Probiotics
Probiotics are live microbes that are believed to play a part in digestion, metabolism and immune system function. They are sometimes referred to as "good bacteria" in the media, but this downplays the truly crucial role the microbiome (the community of microbes that live in our gut) plays. One hypothesis argues that an imbalance in the microbiome (dysbiosis) may be the ultimate cause of UC (see study published in Nature, here) and that probiotics may therefore be part of the solution. This is unlikely to be the whole story, but it is undoubtedly true that probiotics have been shown to play a positive role in the treatment of UC. Many excellent probiotics come in the form of food or drink. We cover the probiotic drinks on the Drink page, but probiotics are also found in food, including sauerkraut, fermented vegetables, tempeh, kimchi, miso, pickles, yoghurt and some cheeses. All such probiotic foods must be consumed unpasteurised (raw), or the probiotic bacteria will have been destroyed. There are many online guides on how to make your own probiotics, with sauerkraut or fermented vegetables good places to begin, in the author's view. The author would recommend eating a (small) portion of probiotic food with every meal, as it is likely to help maintain remission while bringing no downside, acting in a way that is entirely different to how UC drugs work. It is, however, important to note that certain probiotics are not recommended when taking powerful immune-suppressants.
This study (here) is a good one to review, which shows the promise of probiotics in the treatment of ten patients with severe UC, who were unresponsive to other treatments. These ten patients had severely active UC prior to probiotic treatment and many had been heavily pre-treated with drugs. 8/10 patients were experiencing >4 bloody diarrhoea events per day. By week 6, after treatment with probiotics (and a prebiotic - see below), 8/10 patients were passing normal, non-bloody stools and all patients saw large improvements in symptoms, which in the author's view was a quite remarkable result. All patients also saw clinical remission for at least 4 months. This study was uncontrolled (no placebo arm) and the probiotics were administered direct into the colon (one-time), not orally, but the author believes the results speak for themselves and would reiterate the importance of including multiple sources of probiotics (and prebiotics, as below) in your daily diet.
Prebiotics
Prebiotics are carbohydrates or fibre that humans are unable to digest, but that gut bacteria metabolise (eat) in the colon. A diet high in prebiotics should, therefore, support the growth of beneficial gut bacteria, which in turn exert positive effects on the immune system and on the health of the mucosal lining in the colon, extending periods of UC remission (here). Particularly good sources of prebiotics include jerusalem artichokes, garlic, leeks, onion, asparagus, bananas and oat bran, though most plants contain prebiotic fibre to some degree.
There are few studies that have looked at the impact of prebiotics on UC in isolation. One study (here) of 22 patients in remission from UC found that those who were instructed to eat 60g of oat bran per day for 12 weeks experienced statistically lower abdominal pain and reflux compared to the control group (though no one relapsed in either group). The faecal butyrate concentration also increased by 36% at 4 weeks (highly statistically significant). Butyrate (a small chain fatty acid) levels are known to be reduced in active UC, with high levels being associated with maintaining intestinal homeostasis (here), so this 36% increase was a positive sign.
It seems clear to the author that combining foods rich in prebiotics and probiotics is likely to be a core dietary strategy for maximising the chance of keeping UC in remission, given how the former supports healthy growth of the latter. There are commercial products that exist that combine probiotics and prebiotics in supplements, but the author is not aware of any that have run clinical trials and it seems entirely likely to the author that stripping prebiotics and probiotics out of their proper context (whole foods) and mixing with chemicals may not provide the same level of benefit. There are some foods which naturally combine probiotics and prebiotics - sauerkraut and fermented vegetables, for example - and these are much preferred to supplements in the author's opinion, especially if homemade (as they are likely to have a greater diversity of microbes).
All Fruit & Veg
Fruit and vegetables are high in both soluble fibre, which slows the movement of food through the gut and provides food for microbes, and insoluble fibre, which adds bulk to stool and aids its passage (here). Both are important, but if you are suffering from active disease, foods high in insoluble fibre (salad, greens, leaves, skins) are likely to be more painful to eat than foods high in soluble fibre (peeled fruit and veg).
This meta-analysis (here) of 14 case-control studies found that people eating the most vegetables had a 29% lower risk of developing UC compared to those with the lowest intake. Those with the highest consumption of fruit had a 31% lower risk of developing UC compared to those with the lowest. Both of these were statistically significant. A single Danish study (here) which compared 144 UC patients with matched controls found that those who ate daily fruit and daily vegetables were 44% and 49% less likely to develop UC respectively. This meta-analysis (here) of 19 studies (including 1,340 UC patients) also found that high vegetable intake was associated with a lower risk of developing UC.
Based on this evidence and the research by Professor Tim Spector (here), the author recommends trying to eat more than 30 different types of plants a week (mostly fruit and vegetables, but also counting beans, mushrooms, nuts, seeds and herbs). The variety of fibres is thought to be positive for the microbiome, which is good for general health, but also likely to be a positive influence on the course of your UC.
Foods to Eat - Weaker Evidence
Oily Fish
Oily fish, which includes salmon, herring, pilchards and sardines, are known to be good for heart health (here) but there is also evidence that they can have positive effects in UC, though the data is somewhat mixed (here, here). Any effect is likely due to the oily fish omega-3 content, which is a type of fat only found in high concentrations in oily fish, walnuts and flax seeds. More discussion of omega-3 is to be found in the Cooking Oils section.
Few human studies exist, but one study from 2010 (here) tested the effect of 600 grams of salmon consumption in 12 UC patients over 8 weeks. The study researchers found that the ratio of omega-3 to omega-6 fats increased in plasma and rectal biopsies (hardly surprising) and that this was correlated with a significantly reduced SCCAI (measure of colitis severity). Unfortunately, the author does not have access to the full data, but it is an encouraging finding nonetheless. Introducing occasional oily fish into your diet is likely to be incrementally helpful, in the author's view, but other changes as discussed earlier should take priority.
Polyphenols
There are over 8,000 types of polyphenols (here), consisting of four main categories - flavonoids, phenolic acids, lignans and stilbenes. These micronutrients have antioxidant, anti-inflammatory and neuroprotective qualities. They are found in most plants to some degree, though some have very high levels, including berries (especially elderberries and blueberries), cacao powder (best to be low-temperature roasted, or raw), tea/coffee, some nuts and seeds, olives and red wine.
It is challenging to establish the effectiveness of polyphenols in treating UC, as there are so many different types in so many different foods. However, one study (here) administered EGCG (a polyphenol found in green tea) to 19 UC patients (with 4 receiving placebo) for 56 days, finding that by the end of the trial, 10/15 who received EGCG had a response as measured by a disease activity index, compared to 0/4 on placebo. This was statistically significant. The remission rate was 8/15 vs 0/4, but this was not statistically significant, possibly due to the small study size. Outside of humans, many studies have looked at the impact of polyphenols on disease models (here), with flavonoids being of particular interest. Clearly more research is needed, but there are no downsides to eating a diet rich in polyphenol-containing plants.
Wholegrain Carbs
When in a flare, it is encouraged to eat mainly white carbs, as they have been stripped of fibre and so are the least likely food group to cause irritation when passing through the colon. Such white carbs include white pasta, rice, bread and derivatives of other refined grains. However, when in remission, there is evidence that wholegrain carbohydrates (brown bread/rice/pasta and ancient grains such as pearled spelt or barley) are a much better choice. This study (here) showed that daily wholegrain bread consumption was associated with a 58% lower risk of developing UC, when UC patients were matched with controls. This was the strongest food association they found, though in the author's opinion it may be because it is a good metric for finding people who are also more likely to eat other favourable food groups on the list, such as more fruit/veg, probiotics and prebiotics. A final cautionary note - a lot of shop-bought wholegrain bread contains a large number of additives, including emulsifiers, so simpler bakes such as sourdough are likely to be better options, in the author's view.
The Case For Dairy
In recent years, it has become fashionable to eliminate dairy from one's diet, due to its perceived allergenic properties. However, the author has found no evidence that high dairy consumption is associated with UC; for example, this study (here) found no statistical link between consumption of dairy (>2 servings/day) and risk of developing UC after adjusting for confounding factors. Dairy was also not associated with IBD in this (here) very large study of 116k adults across 21 countries. Moreover, while high protein is associated with increased UC risk (Protein), the protein from dairy was not associated with risk of developing IBD in this study (here) of 68k people. The author has also been able to find two randomised clinical trials - the highest standard of evidence - neither of which showed that a dairy-free diet made any difference to induction of UC remission or probability of relapse when in remission (here, here).
It therefore seems to be very clear to the author that there is no point in excluding dairy from your diet if you have UC, especially given that it is an excellent source of many micronutrients that are hard to find elsewhere. The only exception to this would be if you have a diagnosed lactose or dairy protein intolerance or allergy, in which case consuming dairy may well aggravate your UC. This study (here) from 1965 showed that around 20% of patients do benefit from a milk-free diet, which is likely the people who are already intolerant, but that the other 80% did not benefit. It is worth noting that dairy intolerances are far more common among people with ancestry from outside of northern Europe (here) and it is worth considering whether dairy is causing you problems if you are from this demographic.
Some people with UC have claimed to benefit greatly from consumption of raw milk, which is milk that has not been pasteurised to kill harmful bacteria. Proponents of raw milk argue that pasteurisation also kills beneficial bacteria, which can help to extend UC remission - while this may or may not be true, the author has not found any evidence either way from any studies. However, it is undoubtedly true that there are risks to drinking raw milk, with Salmonella, Listeria, Campylobacter or E. coli poisoning all possible. These can be very serious and result in hospitalisation (here). Although the risk is low, it seems to the author that the potential benefit may not be worse the risk, especially given the safer profile of other, much more potent probiotics. It is also worth noting that raw (unpasteurised), hard cheeses are much lower risk than raw milk, and eating these from time to time is very unlikely to cause any issues.
The Role of Sulphur
There is a theory that foods high in sulphur are one of the main drivers of UC, as it is converted to hydrogen sulphide in the colon, which has a number of negative effects, ultimately resulting in inflammation (here). There is some experimental validation for this theory, as it was first discovered in 1985 that animal models which used sulphated dextrans induced colitis in rodents, but the same effect was not seen with non-sulphated dextrans (here). If sulphur does induce UC in humans, it would also explain the higher rates of UC seen among those who eat high levels of processed meats and protein generally, as both contain a lot of sulphur. Foods with high sulphur content include meat, fish, eggs, nuts and dairy (i.e. anything high in protein).
One study (here) examined the impact of high dietary sulphur on 191 UC patients in remission, over the course of one year. It found that the third of people with the highest intake of sulphur had a 176% higher risk of relapse and that this was statistically significant. While this seems very clear, the study caveated the finding, as not all food was scored for sulphur content and there was no such statistical link found between sulphate intake and risk of relapse. Unfortunately, few other studies have looked specifically at sulphur, as it is a very difficult part of the diet to measure.
It is currently the view of the author that 1) research on the sulphur hypothesis is limited, 2) there is clearly some evidence which is supportive of it being important in UC pathogenesis, but 3) optimising for a low sulphur diet is impractical given the difficulty of establishing sulphur levels in different foods, and that it would mean restricting most forms of protein. The author has already recommended not to over-eat protein based on other evidence and has made a strong recommendation to avoid processed meats, which are particularly high in sulphur anyway. Thus, by following better researched advice, such a diet is likely to be relatively low-sulphur in any case. Furthermore, the author would not restrict certain high-sulphur foods that have been shown to be independently beneficial for UC management, such as nuts, seeds, certain vegetables and wholegrains.
What Cooking Oil to Use?
Many studies have looked at the use of different fats/oils in diets and their impact on UC, with some strong associations found. Having reviewed the evidence carefully (see the paragraph below), the author believes that omega-6 fats (mainly linoleic acid (here), found in vegetable oils) should be largely reduced in the diet, and omega-3 fats should be increased (Oily fish). In Western diets, 85-90% of omega-6 fats originate from vegetable oils in the form of linoleic acid (here), being found in processed snacks, fast food and deep-fried foods, so all of these can and should be cut in the author's view. As omega-3 is found mainly in oily fish, it is not a practical source for use as cooking oil, but the evidence shows that extra virgin olive oil (the "extra virgin" is important) is a good choice, due to its high polyphenol content (and much lower omega-6 levels). However, refined olive oil contains a small fraction of the polyphenols found in extra virgin olive oil (here) and should be avoided.
Reviewing the available literature, this study (here) appeared prominently, as it followed 203k people and their diets in 5 European countries over a median of 4 years. During this time, 126 developed UC. Among those, the quarter with the highest intake of linoleic acid (omega-6), there was a 149% higher risk of developing UC, which was both statistically significant and showed a trend across quartiles. This is strong evidence of a real effect, in the author's view, and forms the basis of the "no vegetable oil" recommendation. Furthermore, this meta-analysis (here) of 19 studies encompassing 1,340 UC patients found that high intake of total fats and omega-6 fats were associated with an increased risk of UC. On omega-3 fats, this study (here) of 25k people in the UK detected 22 UC diagnoses after 4.2 years and found that high consumption of DHA (a type of omega-3 fat found in oily fish) was protective against developing UC, with the top third of DHA consumers having a 57% lower chance of developing UC - this was statistically significant. Finally, this study (here), which followed 171k women over 26 years found that the ratio of omega-3 to omega-6 was negatively associated with the development of UC. In other words, the more omega-3 consumed vs omega-6, the less likely a woman was to develop UC, with a 31% lower risk among those fifth with the highest ratio. This study also found no link between consumption of oleic acid (the main fat found in olive oil) and UC.
There is also some evidence to suggest that margarine consumption is significantly associated with UC. In this Japanese study (here), the diets of 101 UC patients were compared to healthy controls; the only food that was found to be statistically significantly associated with development of UC was margarine. A similar study (here) matched 83 UC cases with healthy controls and compared diet before symptoms emerged - it found that moderate and high consumption of margarine increased risk of UC by a huge 12x and 21x respectively. The study was small, which may account for the surprisingly strong findings, but these two studies suggest to the author that margarine is best avoided (as an ultra-processed food, it would be discouraged anyway - see UPFs) in favour of butter or extra virgin olive oil.
The Case For Organic Food
The argument for eating organic fruit and vegetables is that they were not grown with the use of chemical pesticides, herbicides and fertiliser. Residues of these chemicals remain on non-organic plants even after washing and find their way into the human body, as they can be measured in urine and blood. This study (here) showed that among 4,466 participants who had urine measured for pesticides, those who reported more frequent consumption of organic produce had a lower concentration of pesticide measured in their urine (which was statistically significant). Another study (here) took 13 people and randomly allocated them to consume a diet of >80% organic or non-organic food for 1 week before crossing them over. It found that organophosphate (pesticide) levels in urine were 89% lower in the organic group than non-organic group and for one subcategory of pesticide (dimethyl dialkylphosphates), were 96% lower (both highly statistically significant).
A recent paper published in Nature (here) in October 2022 linked a specific herbicide (propyzamide) to growing rates of IBD incidence in the West, while acknowledging it was likely one contributing factor among many. However, this is one of the first papers from a highly reputable journal that has made a link between pesticide intake and UC, and the author would not be surprised if more such links were found in the future. Eating a mainly organic diet would mean a much lower exposure to these chemicals, so if there is a link, it would be a potentially beneficial change. A second potential benefit from eating organic produce may arise from the lower use of plastic in the packaging of food. PFOAs are considered to be "forever chemicals" that persist in the environment and human bodies. They mainly enter our body via contamination (i.e. packaging) of food (and water - see the Drinks section). If your organic food is delivered or purchased without coming into contact with plastic wrappings, this is also likely to reduce your dose of potentially harmful chemicals.
Finally, there is the question of whether eating non-organic meat could result in antibiotics reaching the colon in sufficiently high doses that they may kill gut microbes. Animals have historically been administered large volumes of antibiotics to boost growth, though this is now illegal in the US and most European countries (here). However, antibiotics may still be legally used for various purposes and it is possible that some makes it way into the colon via eating meat. Organic meat is likely to contain materially lower amounts, though the author has not found any studies that have been performed in this area. In the author's view, it may make sense to buy organic for some plant foods, especially for crops that make heavy use of pesticides/herbicides (e.g. oats, fruits, salad leaves), but it probably is not worth it for the occasional serving of meat.
A Note on Veganism
Some people have suggested that the optimal diet for people with UC is to be a vegan (no animal products at all). While there are some positive features, such as higher intake of plants and lower intake of protein, it is also possible to design very poor vegan diets which are unlikely to help and may actually cause harm. For example, a vegan diet consisting of highly processed vegan replacement foods, abundant white carbs, confectionery and processed snacks would be, in the author's view, a very poor diet with UC in mind. Vegans also must carefully plan their diet to ensure they receive adequate B12, vitamin D, omega-3, iron and zinc, or they risk becoming deficient in them, which is commonly observed (here). For people with UC, iron is particularly important due to blood loss, which the body must replace, but the best source of iron is in meat (iron supplements are probably not the answer - see Medicines page). Another consideration is that eating only vegan foods, which restricts certain micronutrients and macronutrients, is an even greater problem for people with UC, where gut absorption is likely to be poorer than in people without UC. The author would therefore recommend a semi-vegetarian diet in those who would choose veganism for ethical reasons, where red meat is eaten perhaps once or twice a month for the iron content, and exceptions are made for oily fish and animal probiotics such as kefir. If those adjustments are made, and care is taken to eat a great variety of fruit and vegetables in their whole form (>30/week being the target, and not as part of a factory-processed meal), then in the author's view, such a diet would be a good compromise to be both beneficial for people with UC while staying true to the ethical vision of veganism.