What To Eat And What To Avoid With IBS

Irritable bowel syndrome (IBS) affects 7% to 21% of the general population.¹ If you suffer from IBS, you know how debilitating it can be and how negatively it can impact your quality of life, especially if you’re still figuring out how food affects you.

Most IBS sufferers find that their symptoms are related to eating specific foods, but it’s not always easy to identify which foods might trigger or worsen IBS symptoms.²

To find out more about which foods to avoid with IBS, which foods may trigger a flare-up, and which foods might improve your IBS symptoms, keep reading.

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First, what is irritable bowel syndrome?

IBS is a chronic gastrological (stomach) condition characterized by changes in bowel habits, often alternating constipation and diarrhea, and abdominal pain in the absence of any other organic disease.² An organic disease has an identifiable cause (such as cancer). In contrast, non-organic illnesses have an underlying cause that’s difficult to pinpoint and may be difficult to measure (such as chronic fatigue).

IBS can be classed into subtypes, such as IBS with constipation; IBS with diarrhea; mixed diarrhea-and-constipation IBS; and unclassified IBS.³ The foods that trigger different types of IBS can vary, but there are common triggers that seem to affect those with any form of IBS.

The precise cause of IBS is unknown, but it seems to have many factors, with the gut microbiome, neurohormones, inflammation, and stress all playing a role.⁴

What to eat if you have IBS

Although most of the dietary management of IBS involves omitting certain foods, adding certain foods to your diet has shown to be beneficial:

Fiber

Fiber for IBS has fallen in and out of favor over the years.⁵ This phenomenon may have to do with the tendency to mistakenly group all fiber types⁶ together under the same label, rather than differentiating the kinds:

Soluble fiber will dissolve in water or other bodily fluids and becomes a gel-like substance. It contributes to healthy gut bacteria.

Insoluble fiber will not dissolve. Instead, it is the “roughage” that won’t break down, and as a result, it helps you eliminate waste.

Soluble fiber can be further divided into “fermentable” and “non-fermentable,” both of which have different effects on your gut.

Fermentable soluble fiber produces gas, leading to abdominal pain and cramping, potentially worsening or triggering an IBS flare-up. Non-fermentable soluble fiber, on the other hand, has a beneficial effect and does not trigger gas production.

Non-fermentable soluble fiber dissolves in water to form a viscous gel that can soften hard stool and alleviate constipation. It can also firm up and bind loose stool to relieve diarrhea.⁷

Fiber as a prebiotic Dietary fiber also acts as a prebiotic, bringing about the growth of beneficial gut bacteria. Prebiotics are like “food” for good bacteria. Since one of the likely causes of IBS is a disrupted gut microbiome, increasing good bacteria in the bowel is likely to have a positive effect.

Fiber also seems to influence the neurohormonal environment of the gastrointestinal tract. Neurohormonal refers to the secretion of gut hormones and their interaction with the nerve cells in the gut. Changes in gut pressure and pH that are triggered by consuming fiber lead to the release of serotonin. Serotonin is known to play an essential role in the perception of pain and discomfort in the colon.

Foods high in non-fermentable soluble fiber

These foods are high in non-fermentable soluble fiber, and incorporating them into your diet may help alleviate your IBS²:

  • Vegetables such as carrots, eggplant, green beans, okra, potatoes, summer squash, sweet potatoes, zucchini, pumpkin, turnip, parsnip

  • Fruit like bananas, blueberries, kiwis, oranges, raspberries, strawberries, mandarins, pawpaw, pineapple

  • Protein in the form of peanuts, sunflower seeds, walnuts

  • Grains like oatmeal and quinoa

If you’re having trouble getting non-fermentable soluble fiber from food alone, you may want to try adding psyllium husk as a dietary supplement. Wheat dextran and acacia fibers are also shown to alleviate symptoms, especially for IBS with constipation.

Probiotics

A review of 18 randomized controlled trials evaluating the use of probiotics to treat IBS showed some improvement in symptoms, mainly bloating and flatulence.¹ 

Probiotics are in many fermented foods, including:

  • Yogurt 

  • Pickles

  • Kombucha

  • Sauerkraut

Peppermint oil

A meta-analysis of studies evaluating the use of peppermint oil has shown that it is effective in reducing some of the pain and cramping associated with IBS. Peppermint oil works on the smooth muscle cells of the colon, relaxing the colon wall and decreasing pain sensitivity.⁴ 

Foods to avoid if you have IBS

Because so many different foods can trigger IBS, it may be challenging to identify which ones aggravate your symptoms. In hope of relief, some people with IBS cut out entire food groups. However, this approach is not ideal, as it could lead you to develop a nutrient deficiency. If you plan to remove an entire food group from your diet, it’s best to do so with guidance from a registered dietician or qualified medical professional.

High FODMAP foods

FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. In simpler terms, these are short-chain carbohydrates (sugars). A diet high in FODMAPs can trigger IBS symptoms, whereas a low-FODMAP diet can reduce abdominal and bowel symptoms.⁷

High-FODMAP foods have poor absorption in the small intestine and get broken down into short-chain fatty acids by gut bacteria. These short-chain fatty acids draw water into the small intestine, slowing down digestion and triggering diarrhea.

High FODMAP foods also have adverse effects on the colon. Bacteria ferments them in the colon, which leads to the production of high levels of hydrogen and methane gas. When comparing breath hydrogen levels between IBS sufferers, and people without IBS, hydrogen levels are much higher in IBS sufferers consuming a high FODMAP diet than for those without IBS who eat a diet high in FODMAPs. Overall, high FODMAP foods have been shown to cause pain, gas, bloating, and altered bowel movement in IBS patients.⁸

The list of high FODMAP foods is extensive, but here are some of the common culprits:

Gas in the gut is caused primarily by the fermentation of poorly digestible carbohydrates in the colon, so most gas-producing foods will turn out to be high in FODMAPs.  

Lactose

Many people who suffer from IBS eliminate dairy from their diet because they believe that lactose may be causing their IBS symptoms.

People who are lactose intolerant — lacking lactase, the enzyme that helps break down lactose — will develop symptoms similar to IBS when they eat dairy. Still, lactose intolerance is different and separate from IBS.

When studied, lactose has not been indicated to impact pure IBS symptoms negatively, and eliminating dairy was not especially effective in relieving IBS symptoms.⁹

Gluten

If you suffer from IBS, you may have tried eliminating gluten from your diet in an attempt to alleviate your symptoms. You might even get some relief by maintaining a gluten-free diet.

However, a review on the effects of gluten-free diets in IBS has shown contradictory results. Some people find relief and others don’t notice any difference.⁹ It seems that different people respond differently to gluten-free diets. So, it may be worth trying a gluten-free diet to see whether or not it reduces your symptoms. Some research suggests that it is not actually the gluten that causes the problem, but the fructans in wheat that trigger pain, discomfort, and bloating.⁹ Fructans are part of the “o” category of FODMAPs (Oligosaccharides).

Fatty foods

Fatty foods are implicated in worsening IBS symptoms, and may trigger IBS. However, a review of studies showed no difference in IBS symptoms after ingestion of fatty foods.

No randomized controlled trials support limiting fat intake in IBS sufferers. Recent research has identified low-grade inflammation as a causative mechanism for IBS and, in light of that, recommended consuming polyunsaturated fatty acids (PUFAs) may improve IBS symptoms.¹⁰ A few sources of these fatty acids include salmon, walnuts, and flaxseed oil.

Spicy foods

Several studies demonstrate that consuming capsaicin (a component in chili peppers) may exacerbate your IBS symptoms, especially abdominal pain and diarrhea. This may not be the case in areas where people routinely eat large amounts of capsaicin, such as certain Asian countries.¹¹

Caffeine

Although there is no evidence to support restricting caffeine in people who suffer from IBS, caffeine (especially in coffee) can have a laxative effect. If you suffer from IBS with diarrhea, coffee may worsen your symptoms. The recommendations around caffeine and IBS are to assess how it affects you and adjust your intake accordingly.¹²

The lowdown

IBS is a complex condition, and symptoms can be both triggered and alleviated by various foods.

Soluble non-fermentable fiber has been shown to be beneficial in controlling symptoms and if you suffer from IBS, you should consider increasing your intake of foods high in non-fermentable soluble fiber.

High-FODMAP foods tend to aggravate symptoms like pain, bloating, flatulence and diarrhea. On the other hand, a low FODMAP diet CAN reduce IBS symptoms and provide relief.

Research indicates that some people with IBS respond positively to a gluten-free diet, so it may be worth testing out and monitoring how restricting gluten impacts your symptoms.

Caffeine and spicy foods can aggravate IBS for some people; again, it’s worth paying attention to how they affect you and adjust your diet accordingly.

There is no solid evidence to eliminate fatty foods or dairy from your diet to improve IBS, however, it is reasonable to decrease intake if you feel that they exacerbate your symptoms.

Because so many different foods can trigger IBS symptoms, it may be tempting to cut out entire food groups or follow a restrictive diet, but doing so could lead to nutritional deficiencies. If you are considering adopting a very restrictive diet, it’s best to get guidance from a professional.

Have you considered clinical trials for Irritable bowel syndrome (IBS)?

We make it easy for you to participate in a clinical trial for Irritable bowel syndrome (IBS), and get access to the latest treatments not yet widely available - and be a part of finding a cure.

Joining community groups and exercise programs for my condition made me feel empowered – but I want to be part of finding a cure.
Peter, 64

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