Mixed IBS: How to Stabilise the Diarrhoea/Constipation Cycle

When your gut can't make up its mind

One day everything grinds to a halt; the next, it all moves too fast. This alternating pattern of diarrhoea and constipation is the hallmark of mixed IBS (IBS-M), one of the most unsettling forms of irritable bowel syndrome. Far from uncommon, IBS affects between 4% and 11% of the global population, and the mixed subtype accounts for a significant proportion of those cases — enough to warrant its own dedicated approach.

The good news: stabilisation is achievable. It doesn't require cutting out everything, but rather a personalised, step-by-step strategy.

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Why is IBS-M so difficult to manage?

IBS arises from multiple interacting factors: visceral hypersensitivity, disrupted gut motility, a dysregulated gut-brain axis, chronic stress, and sometimes alterations in the gut microbiome. In the mixed form, these mechanisms pull in two opposite directions in turn, making any one-size-fits-all approach difficult.

On top of this, several dietary triggers are well established:

• FODMAPs (poorly absorbed fermentable carbohydrates) draw water into the intestine and increase gas production, causing bloating, pain, and transit disruption
• Large meals, caffeine, alcohol, fizzy drinks, and very fatty foods can all worsen symptoms
• Eating speed and irregular mealtimes also play a role

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A low-FODMAP diet: the most evidence-based starting point

The nutritional intervention with the strongest scientific backing for IBS remains the low-FODMAP diet. That said, it is a structured three-phase trial, not a permanent elimination plan.

Phase 1 — Restriction (4 to 6 weeks)

High-FODMAP foods are limited: onions, garlic, wheat, apples, pears, certain pulses, lactose-rich dairy products, and polyols. The aim is to determine whether these fermentable carbohydrates are contributing to your symptoms.

Phase 2 — Methodical reintroduction

FODMAP groups are reintroduced one at a time, gradually, to identify your personal triggers. Not everyone reacts to the same foods.

Phase 3 — Personalisation

A tailored, varied diet is built around your individual tolerances, excluding only what causes problems. Prolonged restriction without this phase can reduce dietary diversity and alter the gut microbiome, which carries its own long-term consequences.

Foods generally better tolerated during the restriction phase: sourdough bread, rice, quinoa, potatoes, oats (in moderate portions), blueberries, kiwis, oranges, carrots, lactose-free milk, and aged cheeses.

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Fibre: choosing the right type at the right time

Not all fibre is equal when it comes to IBS-M. Soluble fibre (oats, psyllium, cooked carrots) is generally preferred, as it helps regulate transit in both directions — softening stools during constipation and potentially slowing things down during bouts of diarrhoea.

Conversely, a sudden increase in insoluble fibre (wheat bran, large quantities of raw vegetables) can worsen pain and bloating in sensitive individuals.

The golden rule: increase fibre intake gradually, monitor your tolerance, and adjust according to whichever symptom is currently dominant.

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Lifestyle habits: often underestimated, but genuinely effective

Beyond diet, several practical habits can make a real difference:

• Eating slowly and chewing thoroughly reduces the amount of air swallowed and aids digestion
• Keeping regular mealtimes helps regulate gut motility
• Avoiding skipped meals prevents sharp spikes in intestinal stimulation
• Staying well hydrated, particularly when constipation is the predominant symptom
• Keeping a food and symptom diary to identify your individual triggers — what aggravates your symptoms may not affect another person with IBS in the same way
• Taking regular exercise, which is well recognised for its beneficial effects on gut motility and digestive stress

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When to see a doctor

IBS with a marked alternating pattern warrants a proper medical assessment, particularly to rule out other conditions such as coeliac disease, sugar malabsorption (including sucrose intolerance), or associated functional disorders. A gluten-free diet is not routinely recommended in IBS without a confirmed diagnosis of coeliac disease.

If symptoms persist despite dietary adjustments, targeted medical treatments are available — including antispasmodics, osmotic laxatives, and antidiarrhoeals — and should be discussed with a healthcare professional.

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A final thought

Mixed IBS cannot be managed with a single rule. It requires method, patience, and self-observation. A well-conducted low-FODMAP diet remains the best starting point. Combined with appropriate lifestyle habits and medical support where needed, it offers a genuine path towards stability.

Your gut has its own logic — take the time to listen to it.