Work With a Professional
The low FODMAP diet is a therapeutic elimination diet that should ideally be followed under guidance from a FODMAP-trained dietitian. Self-guided elimination risks nutritional deficiencies and may not correctly identify your personal triggers. Your GP can refer you to a specialist.
FODMAP stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols - a collection of short-chain carbohydrates that are poorly absorbed in the small intestine. For most people, they cause no problems. But for those with irritable bowel syndrome (IBS), they can trigger bloating, pain, gas, and altered bowel habits.
The low FODMAP diet, developed by researchers at Monash University, is now the most evidence-based dietary intervention for IBS, with around 75% of patients experiencing significant symptom improvement.
What Happens in the Gut
Poor absorption - FODMAPs move through your small intestine largely undigested.
Water drawn into bowel - Their osmotic effect pulls water into the intestine, potentially causing diarrhoea.
Rapid fermentation - Gut bacteria ferment these carbohydrates, producing gas.
Visceral hypersensitivity - People with IBS feel this normal process more intensely, experiencing it as pain and discomfort.
What Does FODMAP Stand For?
- Fermentable - Broken down by gut bacteria, producing gas
- Oligosaccharides - Fructans (wheat, onion, garlic) and GOS (legumes)
- Disaccharides - Lactose (milk, soft cheese, yoghurt)
- Monosaccharides - Excess fructose (apples, honey, high-fructose corn syrup)
- And Polyols - Sugar alcohols (sorbitol, mannitol - stone fruits, mushrooms, sweeteners)
The key insight: it's not that these foods are "bad" - they're healthy for most people. But if you have IBS, your gut responds to them differently.
The Three-Phase Approach
Phase 1: Elimination (2-6 weeks)
Remove all high-FODMAP foods from your diet. This isn't meant to be permanent - it's a diagnostic phase to see if FODMAPs are causing your symptoms. Most people notice improvement within 2-4 weeks if FODMAPs are the issue.
Phase 2: Reintroduction (6-8 weeks)
Systematically reintroduce each FODMAP group, one at a time, to identify your personal triggers. Some people react to fructans but tolerate lactose fine. Others are the opposite. This phase reveals YOUR specific pattern.
Phase 3: Personalisation (Ongoing)
Based on reintroduction results, create a personalised diet that avoids only YOUR triggers while maintaining the widest possible variety. Most people can tolerate more foods than they initially assumed.
Low FODMAP vs High FODMAP Foods
Low FODMAP (Generally Safe)
- Meat, fish, eggs (plain)
- Rice, oats, quinoa
- Potatoes, carrots, courgettes
- Spinach, lettuce, cucumber
- Oranges, strawberries, grapes
- Lactose-free dairy
- Firm tofu
- Maple syrup (small amounts)
High FODMAP (Elimination Phase)
- Onion, garlic, leek
- Wheat, rye, barley
- Apples, pears, mango, watermelon
- Milk, soft cheese, yoghurt
- Beans, lentils, chickpeas
- Mushrooms, cauliflower
- Honey, agave
- Sugar-free gum/mints
Common Mistakes
Staying in Elimination Too Long
The elimination phase should last 2-6 weeks maximum. Extending it indefinitely means missing out on prebiotic fibre that feeds healthy gut bacteria, potentially worsening gut health long-term.
Skipping Reintroduction
Many people feel better during elimination and never bother testing foods back. This leaves them on an unnecessarily restricted diet, avoiding foods that might be perfectly tolerable for them.
Assuming "Low FODMAP" Means "Healthy"
A bacon sandwich on sourdough is technically low FODMAP. That doesn't make it health food. The diet is about managing IBS, not optimising nutrition generally.
Ignoring Portion Sizes
FODMAP content is dose-dependent. A small amount of something might be fine; a larger portion problematic. The Monash FODMAP app gives specific serving size guidance.
The Garlic and Onion Problem
Fructans (found in garlic, onion, wheat) are the most commonly problematic FODMAP group. Unfortunately, they're also the flavour base for most cooking worldwide.
Workarounds exist:
- Garlic-infused oil - Fructans don't dissolve in fat, so the flavour transfers without the FODMAPs
- Green parts of spring onions - Only the white bulb is high FODMAP
- Asafoetida - An Indian spice that mimics onion/garlic flavour
- Chives - Low FODMAP alternative to onion flavour
Is This Diet Right for You?
The low FODMAP diet is specifically for IBS management. It's not a weight loss diet, a general wellness protocol, or appropriate for everyone with digestive issues.
You should consider it if:
- You have a formal IBS diagnosis from your doctor
- Other causes (coeliac disease, IBD) have been ruled out
- You're experiencing persistent bloating, pain, or altered bowel habits
- Dietary triggers seem inconsistent or hard to identify
The Bottom Line
The low FODMAP diet is a clinically validated approach for IBS, with around 75% of patients seeing significant improvement. It works best as a structured three-phase process: eliminate, reintroduce, personalise. The goal isn't permanent restriction but identifying YOUR specific triggers so you can eat as widely as possible while managing symptoms. Work with a FODMAP-trained dietitian for best results - they can guide reintroduction and prevent unnecessary restriction.
References
- Monash University. (2024). The Low FODMAP Diet. monashfodmap.com
- Halmos, E.P., et al. (2014). A diet low in FODMAPs reduces symptoms of irritable bowel syndrome. Gastroenterology, 146(1), 67-75. doi:10.1053/j.gastro.2013.09.046
- British Dietetic Association. (2023). Irritable Bowel Syndrome and Diet. bda.uk.com
- NICE. (2017). Irritable bowel syndrome in adults: diagnosis and management. Clinical guideline CG61. nice.org.uk/guidance/cg61
