Episode 248 – The 2026 Guide to IBS & FODMAPs

IBS Basics

IBS stands for irritable bowel syndrome. It’s a functional gut disorder, which means tests often show no structural problems even though gut function is impaired. It affects about 3.8 to 9.2% of the population and appears around 1.5 times more often in women than men.

Common symptoms include bloating, lower abdominal pain, abdominal distension, excessive gas, and changes in bowel habits. Those bowel changes can look like constipation, diarrhoea, or a mix.

How IBS Gets Diagnosed

Diagnosis usually relies on symptom criteria after ruling out other gastrointestinal conditions such as coeliac disease and inflammatory bowel disease.

The Rome IV criteria guides diagnosis. It focuses on recurrent abdominal pain, on average at least one day per week in the last three months, plus two or more of the following:

Pain related to defecation
Pain linked with a change in stool frequency
Pain linked with a change in stool form

IBS Types

IBS can show up in different patterns:

Constipation-predominant
Diarrhoea-predominant
Mixed (alternating)
Unclassified

Since symptoms vary, the goal is to reduce the symptoms that matter most for the person.

What are FODMAPs?

FODMAPs are fermentable carbohydrates and sugar alcohols. They can trigger symptoms because they ferment quickly in the gut or draw water into the bowel.

The Five FODMAP Groups

Fructans

These ferment rapidly. Common sources include onion, garlic, plus wheat, rye, barley, and inulin.

GOS (Galacto-Oligosaccharides)

Found in legumes, chickpeas, soy milk, and cashews. These tend to be malabsorbed to some degree and can increase gas and bloating, although tolerance can improve.

Lactose

Found in milk, yoghurt, ice cream, soft cheeses, and custard. Hard cheeses tend to be low lactose. Lactose can draw water into the gut, which may worsen symptoms.

Fructose

It usually triggers symptoms when fructose exceeds glucose. That ratio makes it harder to guess. Sources mentioned include honey, apples, mangoes, pears, and high fructose corn syrup.

Polyols

Sugar alcohols such as sorbitol and mannitol. These absorb slowly and can act like laxatives. Sources mentioned include peaches, blackberries, mushrooms, and cauliflower.

For a detailed list, the Monash FODMAP app offers a paid option that’s user-friendly and regularly updated.

Low FODMAP Options

Traditional Low FODMAP Approach

This approach runs in phases:

Elimination phase: go fully low FODMAP for about two to four weeks (it’s low FODMAP, not no FODMAP)
Reintroduction phase: add foods back one at a time
Washout periods: use washouts to confirm whether the added food caused symptoms
Personalisation phase: build a long-term plan based on what you tolerate

Gentle Low FODMAP Approach

This method targets the high FODMAP foods you eat most often and swaps out common triggers without making you track every ingredient.

Common swaps include:

Vegetables: onion, garlic, leeks, cauliflower, mushrooms
Fruits: apples, pears, stone fruits, watermelon
Grains: large amounts of wheat and rye
Dairy: lactose-containing foods
Legumes

Because it’s less restrictive, it often feels easier to stick to. It also keeps more prebiotic-rich foods in the diet.

What the Research Shows

Recent research suggests several strategies can reduce IBS symptoms. Low FODMAP can help, but it isn’t the only useful option.

Gentle vs Full Low FODMAP

A randomised controlled trial referenced on the Monash website in December 2025 found similar symptom improvements between a full low FODMAP diet and a gentle version. However, the gentle approach had a higher completion rate.

One important detail: about 60% of participants noticed improvements in that study. Success rates often get quoted around 50 to 80%, and diarrhoea-predominant IBS often responds better than constipation-predominant IBS.

Mediterranean Diet vs Low FODMAP

A 2025 randomised controlled trial compared a Mediterranean diet with a full low FODMAP diet in diarrhoea-predominant IBS over four weeks.

The low FODMAP group reported an 81.8% rate of large improvement. Meanwhile, 73% of the Mediterranean diet group also reported large improvements. That finding suggests a Mediterranean-style pattern may help many people, even without strict FODMAP elimination.

Starch and Sucrose Reduced Diet

A 2024 study compared a starch and sucrose reduced diet with low FODMAP. Both groups showed around a 79% improvement rate.

Gut-Directed Hypnotherapy

A 2016 randomised clinical trial found gut-directed hypnotherapy produced similar symptom relief to a low FODMAP diet. This highlights how strongly the gut-brain axis can influence symptoms.

Why Reintroduction Matters

Low FODMAP cuts out many prebiotic fibre sources that feed beneficial gut bacteria. Therefore, reintroduction helps protect gut health and reduces the risk of staying overly restrictive long-term.

Probiotics

Probiotics may help, although results tend to be modest. They often suit people with milder symptoms.

Bifidobacterium lactis showed about a 30% improvement across a few randomised controlled trials discussed in the Monash FODMAP course
Lactobacillus plantarum looked more inconsistent, with a possible reduction in stool frequency but fewer other benefits

A systematic review of 44 studies reported:

80.4% success when probiotics were used alongside low FODMAP
71% success for low FODMAP alone
65% success for probiotics alone

More recent multi-strain research looks more promising than older single-strain studies. One major review also found most benefits appear within the first two to four weeks, which makes short trials more practical.

Fibre and Hydration

Fibre type and fibre intake can shape IBS symptoms. Insoluble fibre adds bulk to stool, while soluble fibre forms a gel and can help with both constipation and diarrhoea.

When increasing fibre, doing it slowly can help. A common pace mentioned was no more than 5 grams per week, while staying hydrated. Since low FODMAP can reduce fibre intake, planning fibre becomes even more important.

Supplement options:

Psyllium: often helps constipation and may mildly help diarrhoea by forming a gel
Partially hydrolysed guar gum: tends to be well tolerated, offers a prebiotic benefit, and causes less fermentation for many people

Constipation Tools

For constipation, osmotic laxatives can help. Products with polyethylene glycol, such as Osmolax or Movicol, can improve stool consistency and frequency. They can also reduce bloating indirectly by improving constipation.

Unlike stimulant laxatives, osmotic laxatives draw water into the bowel rather than forcing bowel contractions. They were described as safe over three to six months while dietary changes take effect.

Stress and the Gut-Brain Axis

IBS symptoms often link with the gut-brain axis. Visceral hypersensitivity can make normal gut sensations feel more intense. Because of that, stress reduction and nervous system regulation can reduce symptoms.

Strategies include:

Reducing stress
Mindfulness
Breathing exercises

A 2025 consensus paper described gut-directed hypnotherapy as a first-line treatment for people who haven’t responded to dietary changes.

L-Glutamine

L-glutamine feeds enterocytes, the cells lining the small intestine. Some IBS symptoms may relate to gastrointestinal permeability. Short-term dosing discussed included 3 to 5 grams, three times per day.

Earlier randomised controlled trials were described as positive, mainly in post-infectious diarrhoea-predominant IBS. However, a meta-analysis on intestinal permeability suggested higher doses, around 30 grams per day, may be needed to significantly reduce permeability. Since evidence is still developing, this tends to suit a smaller subset rather than being a universal recommendation.

Movement

Gentle daily movement can support bowel regularity, especially in constipation. Walking can still help even for people who train regularly, including on rest days. Yoga was also mentioned as having meaningful benefit for IBS, potentially through both movement and relaxation.

When to Get Support

Since IBS is often multifactorial, different people need different combinations of strategies. Working with a dietitian who understands IBS can help prioritise what to trial first and reduce unnecessary restriction.