What FODMAPs Are
FODMAP stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides, And Polyols — a collection of short-chain carbohydrates that are poorly absorbed in the small intestine. When these molecules reach the colon, they are rapidly fermented by resident bacteria, producing hydrogen and methane gases, and they draw water into the intestinal lumen through osmosis. In individuals with visceral hypersensitivity (as in IBS), this combination of gas and fluid distension triggers pain, bloating, and altered bowel habits.
The Five FODMAP Groups
Oligosaccharides: fructans (wheat, onion, garlic) and galacto-oligosaccharides (legumes). These are always malabsorbed to some degree, as humans lack the enzymes to fully digest them. Disaccharides: lactose (milk, yoghurt, soft cheese) — malabsorbed only in people with lactase deficiency. Monosaccharides: excess fructose (apples, pears, honey, mango) — malabsorbed when fructose exceeds glucose in the food. Polyols: sorbitol and mannitol (stone fruits, mushrooms, cauliflower, sugar-free sweeteners) — passively absorbed with limited capacity.
The Three-Phase Protocol
Phase 1 — Elimination (2 to 6 weeks): All high-FODMAP foods are reduced simultaneously. This is diagnostic — if symptoms do not improve within 2 to 6 weeks, FODMAPs are likely not the primary driver and the restriction should stop. Response rates are typically 50 to 80 percent in IBS patients.
Phase 2 — Reintroduction (6 to 10 weeks): Individual FODMAP groups are reintroduced one at a time, in escalating doses, over 3-day challenges separated by washout periods. This phase identifies which specific FODMAP groups trigger symptoms and at what dose. Most patients find they are sensitive to only 1 to 2 groups, not all five.
Phase 3 — Personalisation (ongoing): Based on reintroduction results, patients develop a long-term diet that restricts only their specific triggers, at their specific threshold doses, while maintaining maximum dietary diversity.
Why Long-Term Restriction Is Harmful
The elimination phase was never designed as a permanent diet. Prolonged full FODMAP restriction reduces dietary fibre variety (particularly fructans and GOS, which are potent prebiotics), decreases Bifidobacterium abundance, reduces overall microbial diversity, and carries risks of nutritional inadequacy and disordered eating. A 2017 study in Gut confirmed that long-term FODMAP restriction significantly reduced Bifidobacterium populations compared to habitual diet — a concerning finding given Bifidobacterium's role in immune modulation and barrier function.
Who Should Use It
The low-FODMAP diet is indicated for IBS (diagnosed using Rome IV criteria) when first-line dietary advice (regular meals, adequate hydration, limiting caffeine and alcohol) has been insufficient. It should be supervised by a dietitian trained in the FODMAP protocol. It is NOT recommended for IBD (unless IBS-type symptoms coexist with quiescent disease), eating disorders, or general wellness optimisation.