The lowdown on the low-FODMAP diet

Ever wondered if the low FODMAP diet could be the answer to your gut symptoms? If you’ve been dealing with bloating, excess wind, or unpredictable toilet habits, chances are you’ve come across it. It’s one of the most researched dietary tools for Irritable Bowel Syndrome (IBS) – which affects 5-10% of people globally – with studies showing up to 70% of people experiencing symptom relief in the short term. That may come as no surprise, given that around 9 in 10 people with IBS report that food is one of their main symptom triggers.

But despite its evidence base, the low FODMAP diet is often misunderstood and misused. Some view it as a cure-all, while others see it as another restrictive “wellness” trend. The truth is somewhere in between. So let’s cut through the noise. Here’s what the low FODMAP diet really is, what it definitely isn’t, who exactly it is for and how to approach it in a way that achieves symptom relief while also supporting both your gut and your overall health.

What actually is the low FODMAP diet?

FODMAP stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols. These are types of carbohydrates that are naturally present in foods like garlic, onions, apples, milk, and even some non-sugar sweeteners.

These carbohydrates, which include some types of fibre,  aren’t fully absorbed in the small intestine (where most other nutrients are usually taken up i.e. move from your gut into your blood system to feed your brain, skin etc.). Instead, they move further down your intestine into the next section, known as the large intestine. Depending on the type of FODMAP, some pull water from your blood system into your gut, rather than the typical scenario where water moves in the opposite direction. This, in turn, can increase the pressure in your gut. The large intestine is also where your gut microbes get to work, fermenting anything that isn’t absorbed higher up your gut, FODMAPs included. While bacteria fermenting FODMAPs is a perfectly natural process (it happens in everyone’s gut), when you suffer from IBS, which typically includes a sensitive gut lining, more scientifically known as visceral hypersensitivity, it can lead to symptoms like bloating, gas or tummy pain. Importantly, these carbs (FODMAPs) aren’t “bad”. In fact, they’re found in many nutritious plant foods, and several FODMAPs (namely the oligosaccharides) are prebiotic, meaning they help nourish your anti-inflammatory gut microbes. But if you have IBS, which you can liken to somewhat of a gut injury, adding too many in your diet is like trying to lift weights with an injured bicep –  it can exacerbate your symptoms.

The low FODMAP diet involves temporarily reducing your intake of these fermentable carbs. It’s done in three stages under the guidance of a gut-trained dietitian:

• Restriction phase (2–6 weeks): cut back on all high FODMAP foods.
• Reintroduction phase (6–10 weeks): test FODMAP groups one by one to identify your personal triggers.
• Personalisation phase: return to the most varied diet possible, including all the FODMAPs at the dose you tolerate. Over time, you work to build up your tolerated dose, like you would your exercise post-injury.

As we’ll cover in more detail below, it’s essential to be aware that this diet is not for life. It’s a clinical tool used to provide relief to those with an IBS flare and identify tolerance thresholds for common food triggers. However, given its restrictive nature (which can lead to your microbes missing out on many of the foods that support a diverse gut microbiome and heal an injured gut), it’s not a long-term eating plan.

What’s the evidence?

The low FODMAP diet is one of the few dietary strategies with strong evidence for IBS management. Studies show that up to 70% of people with a confirmed IBS diagnosis see an improvement in symptoms within 4-6 weeks when it’s carried out properly.

The research surrounding this diet is always evolving. When we first wrote about the low FODMAP diet, the evidence was almost entirely based on IBS, including several trials undertaken by Megan’s colleagues and research team at King’s College London. Now, new studies suggest that it may also help ease gut symptoms in people with endometriosis — although more trials are needed before it can be recommended as part of standard care.

That said, it’s no magic bullet, and it doesn’t address IBS nor endometriosis at its root cause. Think of it as a tool to help you ease an IBS flare while you work on retraining and restrengthening your gut – it’s not a lifelong eating plan.

Is the low FODMAP diet right for you?

Before jumping in, there are a few important things to consider:

• Rule out other conditions first. Always speak to your GP/ family physician to exclude things like coeliac disease or inflammatory bowel disease before assuming IBS. Your healthcare team can also review whether you fit the formal diagnostic criteria for IBS. 
• Start with first-line strategies. Up to half of people with IBS improve with simpler tweaks, such as:
  
  • Managing stress and supporting your gut–brain axis 
  • Eating smaller, but more regular meals 
  • Spreading fibre intake evenly throughout the day 
  • Choosing whole fruit over juices and smoothies (aim for just one piece per sitting) 
  • Staying hydrated 
  • Cutting down on known triggers like spicy food, alcohol, caffeine and certain sweeteners (such as those found in sugar-free chewing gum) 
• Check in on your relationship with food. If you have a history of disordered eating, or food already causes anxiety, seek specialist support first. Restriction can trigger a relapse of an eating disorder and may do more harm than good.

The low FODMAP diet is also unlikely to be appropriate if:

• You don’t have a confirmed IBS diagnosis 
• You’re underweight or at risk of malnutrition 
• You’re already on a very restricted diet

• You don’t have access to dietitian support (the less restrictive versions, such as FODMAP-lite, may be more suitable).

As we covered above, if you don’t have IBS, there’s absolutely no need to avoid FODMAPs. For most people, they’re found in many gut-nourishing foods that your microbes transform into messenger molecules that do everything from strengthen your gut lining to regulate your appetite and sex hormones.