FODMAP

FODMAPs are poorly absorbed in the small intestine and subsequently fermented by the bacteria in the distal small and proximal large intestine. This is a normal phenomenon, common to everyone. The resultant production of gas potentially results in bloating and flatulence.^[6]

Nevertheless, although FODMAP can cause certain digestive discomfort in some people, not only do they not cause intestinal inflammation, but they avoid it, because they produce beneficial alterations in the intestinal flora that contribute to maintain the good health of the colon.^[3][4][5]

FODMAPs are not the cause of irritable bowel syndrome nor other functional gastrointestinal disorders, but rather a person develops symptoms when the underlying bowel response is exaggerated or abnormal.^[6]

Fructose malabsorption and lactose intolerance may produce IBS symptoms through the same mechanism but, unlike with other FODMAPs, poor absorption of fructose is found in only a minority and, in certain populations, notably those of European descent, lactose intolerance is found in only a minority.^[14] Many who benefit from a low FODMAP diet need not restrict fructose or lactose. It is possible to identify these two conditions with hydrogen and methane breath testing and thus eliminate the necessity for dietary compliance if possible.^[6]

The significance of sources of FODMAPs varies through differences in dietary groups such as geography, ethnicity and other factors.^[6] Commonly used FODMAPs comprise the following:^[15]

• oligosaccharides, including fructans and galacto-oligosaccharides;
• disaccharides, including lactose;
• monosaccharides, including fructose;
• polyols, including sorbitol, xylitol, and mannitol.

Sources of fructans include wheat, rye, barley, onion, garlic, Jerusalem and globe artichoke, beetroot, dandelion leaves, the white part of leeks, the white part of spring onion, brussels sprouts, savoy cabbage and prebiotics such as fructooligosaccharides (FOS), oligofructose and inulin.^[6][16][17] Asparagus, fennel, red cabbage and radicchio contain moderate amounts but may be eaten if the advised portion size is observed.^[17]

Pulses and beans are the main dietary sources (though green beans, canned lentils, sprouted mung beans, tofu (not silken) and tempeh contain comparatively low amounts).^[17][16] Supplements of the enzyme supplement alpha-galactosidase may reduce symptoms^[18] (if brands containing other FODMAPs, such as polyol artificial sweeteners, are avoided).

Polyols are found naturally in some fruit (particularly stone fruits), including apples, apricots, avocados, blackberries, cherries, lychees, nectarines, peaches, pears, plums, prunes, watermelon and some vegetables, including cauliflower, mushrooms and mange-tout peas. They are also used as bulk sweeteners and include isomalt, maltitol, mannitol, sorbitol and xylitol.^[6][16] Cabbage, chicory and fennel contain moderate amounts but may be eaten if the advised portion size is observed.^[17]

People following a low-FODMAP diet may be able to tolerate moderate amounts of fructose and lactose, particularly if they have lactase persistence.

A low-FODMAP diet consists in the global restriction of all fermentable carbohydrates (FODMAPs).^[6]

Below are low-FODMAP foods categorized by group according to the Monash University "Low-FODMAP Diet".^[17][19]

• Vegetables: alfalfa, bean sprouts, green beans, bok choy, capsicum (bell pepper), carrot, chives, fresh herbs, choy sum, cucumber, lettuce, tomato, zucchini, the green parts of leeks and spring onions
• Fruits: orange, grapes, melon
• Protein: meats, fish, chicken, tofu (not silken), tempeh
• Dairy: lactose-free milk, lactose-free yoghurts, hard cheese
• Breads and cereals: rice, crisped rice, maize/corn, potatoes, quinoa and gluten-free breads made with their flours. Oats and spelt are relatively low in FODMAPs.
• Biscuits (cookies) and snacks: made with flour of cereals listed above, without high FODMAP ingredients added (such as onion, pear or honey).
• Nuts and seeds: almonds (no more than 10 nuts per serving), pumpkin seeds; not cashews or pistachios
• Beverage options: water, coffee, tea

Other sources confirm the suitability of these and suggest some additional foods.^[20]

A low-FODMAP diet might help to improve short-term digestive symptoms in adults with irritable bowel syndrome,^{[7][8][9][10]} but its long-term follow-up can have negative effects because it causes a detrimental impact on the gut microbiota and metabolome.^{[2][8][10][11]} It should only be used for short periods of time and under the advice of a specialist.^[21] More studies are needed to evaluate its effectiveness in children with irritable bowel syndrome.^[7] There is only a little evidence of its effectiveness in treating functional symptoms in inflammatory bowel disease from small studies which are susceptible to bias.^[22][23] More studies are needed to assess the true impact of this diet on health.^[8][10]

In addition, the use of a low-FODMAP diet without medical advice can lead to serious health risks, including nutritional deficiencies, cancer risk or even mortality. A low-FODMAP diet can ameliorate and mask the digestive symptoms of serious diseases that usually present digestive symptoms similar to those of irritable bowel syndrome, such as celiac disease, inflammatory bowel disease and colon cancer. It is crucial to conduct a complete medical evaluation before starting a low-FODMAP diet to ensure a correct diagnosis and that the appropriate therapy can be undertaken.^[12] This is especially relevant in the case of celiac disease. Since the consumption of gluten is suppressed or reduced with a low-FODMAP diet, the improvement of the digestive symptoms with this diet may not be related to the withdrawal of the FODMAPs, but of gluten, indicating the presence of an unrecognized celiac disease, avoiding its diagnosis and correct treatment, with the consequent risk of several serious health complications, including various types of cancer.^[12][13]

A low-FODMAP diet is highly restrictive in various groups of nutrients, can be impractical to follow in the long-term and may add an unnecessary financial burden.^[23]

The basis of many functional gastrointestinal disorders (FGIDs) is distension of the intestinal lumen. Such luminal distension may induce pain, a sensation of bloating, abdominal distension and motility disorders. Therapeutic approaches seek to reduce factors that lead to distension, particularly of the distal small and proximal large intestine. Food substances that can induce distension are those that are poorly absorbed in the proximal small intestine, osmotically active, and fermented by intestinal bacteria with hydrogen (as opposed to methane) production. The small molecule FODMAPs exhibit these characteristics.^[6]

Over many years, there have been multiple observations that ingestion of certain short-chain carbohydrates, including lactose, fructose and sorbitol, fructans and galactooligosaccharides, can induce gastrointestinal discomfort similar to that of people with irritable bowel syndrome. These studies also showed that dietary restriction of short-chain carbohydrates was associated with symptoms improvement.^[24]

These short-chain carbohydrates (lactose, fructose and sorbitol, fructans and GOS) behave similarly in the intestine. Firstly, being small molecules and either poorly absorbed or not absorbed at all, they drag water into the intestine via osmosis.^[25] Secondly, these molecules are readily fermented by colonic bacteria, so upon malabsorption in the small intestine they enter the large intestine where they generate gases (hydrogen, carbon dioxide and methane).^[6] The dual actions of these carbohydrates cause an expansion in volume of intestinal contents, which stretches the intestinal wall and stimulates nerves in the gut. It is this 'stretching' that triggers the sensations of pain and discomfort that are commonly experienced by IBS sufferers.^[2]

The FODMAP concept was first published in 2005 as part of a hypothesis paper.^[1] In this paper, it was proposed that a collective reduction in the dietary intake of all indigestible or slowly absorbed, short-chain carbohydrates would minimise stretching of the intestinal wall. This was proposed to reduce stimulation of the gut's nervous system and provide the best chance of reducing symptom generation in people with IBS (see below). At the time, there was no collective term for indigestible or slowly absorbed, short-chain carbohydrates, so the term 'FODMAP' was created to improve understanding and facilitate communication of the concept.^[1]

The low FODMAP diet was originally developed by a research team at Monash University in Melbourne, Australia.^[17] The Monash team undertook the first research to investigate whether a low FODMAP diet improved symptom control in patients with IBS and established the mechanism by which the diet exerted its effect.^[2][26] Monash University also established a rigorous food analysis program to measure the FODMAP content of a wide selection of Australian and international foods.^[27][28][29] The FODMAP composition data generated by Monash University updated previous data that was based on limited literature, with guesses (sometimes wrong) made where there was little information.^[30]

• Description of Monash University Low FODMAP diet and lists of available resources
• Stanford University: The Low FODMAP Diet