Low-FODMAP Diet: The Three Phases, the IBS Trials and Indian High and Low FODMAP Foods

The low-FODMAP diet is a three-step eating plan used to manage irritable bowel syndrome (IBS) that a doctor has diagnosed. For 2 to 6 weeks, foods rich in certain fermentable carbohydrates are swapped for lower alternatives; each group is then tested back for three days at a time; and only the groups that cause trouble stay restricted. In a randomised trial from Ludhiana, 62.7 per cent of patients responded at four weeks against 40.8 per cent on traditional advice. It is a test, not a permanent way of eating, and one of the entries in NNWA's handbook of diets.

What are FODMAPs?

FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. Monash University in Australia, whose researchers developed the concept, describes them as short-chain carbohydrates that are not completely digested or absorbed in the intestine. They occur naturally in ordinary, nutritious foods, and Monash notes that most people eat high-FODMAP foods every day without any problem.

How do FODMAPs cause symptoms?

By pulling water into the gut and feeding gas-producing bacteria. Monash explains that FODMAPs move slowly through the small intestine and attract water, and that bacteria in the large intestine ferment them rapidly and release gas. This happens in everyone. The difference in IBS is a gut wall that is unusually sensitive, or a gut that moves its contents too fast or too slowly, so the same stretch from water and gas is felt as pain, bloating, wind and a change in bowel habit.

That mechanism explains two features of the diet. It lowers a load; it does not remove an allergen, so portion size matters and small amounts are often tolerated. And it does nothing to the underlying sensitivity, which is why the diet manages symptoms and makes no claim to end the condition. NNWA's introduction to gut health covers the wider picture.

The three phases of the diet

Monash calls them steps and reviews by dietitians call them restriction, reintroduction and personalisation. The order is fixed and the first phase is the shortest. A practice review in the Journal of Human Nutrition and Dietetics notes that the stages can be covered in at least two appointments with a dietitian.

What does the trial evidence in IBS show?

It shows a real effect on symptoms over a few weeks. In the 2014 Monash feeding trial, 30 people with IBS ate a low-FODMAP diet and a typical Australian diet for 21 days each, in random order, with almost all food provided. Their overall symptom score on a 100 mm scale was 22.8 mm on the low-FODMAP diet and 44.9 mm on the comparison diet, and bloating, pain and wind all fell. Healthy volunteers felt no difference.

A harder test came from a 2017 trial in two hospitals in the United Kingdom, which compared the diet with a sham diet that restricted a similar number of foods, in 104 patients over four weeks. Adequate relief was reported by 57 per cent on the low-FODMAP diet and 38 per cent on the sham diet, a difference that narrowly missed statistical significance, while the symptom severity score was clearly lower on the low-FODMAP diet.

How strong is this? Moderate, with clear limits. The 2022 network meta-analysis in Gut found the diet ranked first against habitual diet and other dietary advice, but its authors point out that most trials were run in hospital clinics and did not study reintroduction or personalisation at all. Trials are short, and a diet is hard to blind. The American College of Gastroenterology's guideline accordingly recommends a limited trial of the diet, not open-ended use.

What is the evidence from India?

Thin but encouraging. The one Indian randomised trial in IBS, from Dayanand Medical College in Ludhiana, assigned 101 adults with diarrhoea-predominant IBS to a strict low-FODMAP diet or traditional dietary advice for four weeks, then guided the diet group through reintroduction until week 16. Responders were more common on the diet at both points. Compliance was 93 per cent at four weeks and 64 per cent at sixteen. Energy, carbohydrate, fat and fibre intake fell during the strict phase and recovered by the end.

The 2023 Indian consensus statements on IBS, issued by the Indian Neurogastroenterology and Motility Association, call Indian studies of the diet scanty and ask for more before it is applied widely. They note that the northern Indian diet is highest in FODMAP content and the north-eastern lowest, with southern and eastern diets also low, and judge the diet hardest to implement in the north. Community surveys cited there put IBS at 0.4 to 4.2 per cent of Indian adults.

A survey from a Mumbai hospital adds a caution. Among 204 patients with IBS and 400 healthy adults asked about foods usually labelled high-FODMAP, some intolerance was reported by 72.1 per cent of patients and 44.8 per cent of healthy people, but to different foods in different people: pulses by 31.9 per cent of patients, milk by 29.9 per cent, garlic by 13.2 per cent and onion by 8.3 per cent. The authors conclude that the individual should be the final judge of an elimination diet.

High and low FODMAP foods on an Indian plate

FODMAP content cannot be guessed from how a food looks or tastes; Monash measures it in the laboratory and publishes a sample list. The table below takes that list and keeps the foods an Indian kitchen uses. It is a starting map, not a full chart: NNWA's Indian IBS diet chart sets out the day-to-day plan, and this entry does not repeat it.

Three gaps should be stated plainly. The public list does not rate individual dals, paneer, millets, idli or dosa, and a review by Indian gastroenterologists in 2019 said there is only limited data on the FODMAP content of Indian foods. The list rates foods at a set serving, so a low food can become high in a large helping. And roti made from whole wheat atta is not named; Monash lists wheat-based breads as high, which is why wheat is usually reduced in the first phase.

An Indian day in the restriction phase

The day below is illustrative and uses only foods on Monash's lower list, to show the shape of a restriction-phase day and where the difficulty lies. Plain rice is assumed from the list's rice-based products and should be confirmed with the dietitian. Cooking is done without onion or garlic.

Set that day beside ICMR-NIN's My Plate for the Day, which allots 300 ml of milk or curd and 85 g of pulses on a 2,000 kcal vegetarian diet. Both are restricted here. For a vegetarian the first phase therefore removes the two main protein foods together, which is the practical reason the Indian consensus doubts how easily the diet transfers, and the reason this phase is kept short.

Why is it a short, supervised diet?

Because the strict phase costs something even when it works. In the Indian trial, energy and fibre intake dropped during the four strict weeks. In the 2017 trial from the United Kingdom, stool samples from people on the diet held fewer Bifidobacterium bacteria than samples from the sham group. And adherence fell from 93 to 64 per cent as the weeks went on. A diet that lowers intake, shifts gut bacteria and is hard to keep is not one to stay on by default.

Calcium shows the arithmetic. ICMR-NIN's 2020 allowance for adults is 1,000 mg a day, and whole cow's milk holds 118 mg per 100 g in the Indian Food Composition Tables 2017, so the 300 ml of milk or curd in My Plate, taken as about 300 g, supplies roughly 350 mg. Take it out without a replacement and a third of the allowance goes with it. The calcium table for Indian foods lists other sources, and the handbook's entries on dietary fibre and probiotics cover the other two concerns.

This is why Monash states that the diet should be followed under a dietitian with skills in IBS, and why the Indian review tells physicians to involve a dietitian whenever the diet is planned.

A worked example: reading a reintroduction diary

This is an illustrative case, not a real person. Take a 34-year-old vegetarian schoolteacher in Chennai whose gastroenterologist has diagnosed diarrhoea-predominant IBS and referred her to a hospital dietitian. She follows the restriction phase for four weeks, inside the 2 to 6 week window, and her bloating settles. Six groups remain to be tested. At three days each that is at least 18 days of challenges, plus whatever gap the dietitian sets between them.

Her long-term diet is therefore not low-FODMAP at all. Milk, curd, fruit and modest portions of dal are back, and only large amounts of onion, garlic, wheat and mushroom are held down. The amounts are examples; the dietitian sets the real ones.

Common myths and mistakes

The commonest mistake is never leaving the first phase. The trials that show benefit are short, the 2022 meta-analysis found that reintroduction has hardly been studied, and the whole purpose of the plan is to arrive at the least restrictive diet that keeps symptoms quiet.

Safety: see a doctor first, and who the diet does not suit

See a doctor before any restriction, because other conditions look like IBS. Monash names coeliac disease, inflammatory bowel disease, endometriosis and bowel cancer among them. The Indian consensus lists the alarm features that call for thorough investigation: symptoms that begin after the age of 45, anaemia, blood in the stool, unintended weight loss, symptoms that wake you at night, fever, a lump in the abdomen, and a family history of bowel cancer.

The diet is a poor fit for some people even with a diagnosis. Anyone who is underweight, has or has had an eating disorder, is pregnant or breastfeeding, or is planning it for a child or an older relative should not restrict food groups without the treating team. People with diabetes should have fruit and cereal swaps checked against their own plan. The diet does not replace prescribed medicine and does not cure IBS; it identifies triggers so that symptoms can be managed.

Learning this with NNWA

Digestive health and therapeutic diets are among the subjects taught at NNWA, a private skill academy in Kolkata whose classes run online in English and Hindi. Its programmes, such as the Gut Health course, prepare people to coach healthy clients and to send anyone with ongoing bowel symptoms to a doctor. No NNWA course is a degree or a dietitian qualification.