FODMAP

FODMAPs are short chain carbohydrates (oligosaccharides), disaccharides, monosaccharides and related alcohols that are poorly absorbed in the small intestine. These include short chain (oligo-) saccharide polymers of fructose (fructans) and galactose (galactans), disaccharides (lactose), monosaccharides (fructose), and sugar alcohols (polyols) such as sorbitol, mannitol, xylitol and maltitol.

The term FODMAP is an acronym, deriving from "Fermentable Oligo-, Di-, Monosaccharides And Polyols." These carbohydrates are commonly found in the modern western diet. Some evidence has been presented that the restriction of these FODMAPs from the diet may have a beneficial effect for sufferers of irritable bowel syndrome and other functional gastrointestinal disorders (FGID), including one low FODMAP diet.

A low FODMAP diet has been shown in studies to be efficacious in short-term management of many individuals with FGID, but this diet can adversely affect the gut microbiota and nutrient intake. Currently, the long-term efficacy and safety of low FODMAP diet are not established.

History of FODMAPs

Over many years, there have been multiple observations that ingestion of certain short-chain carbohydrates, including lactose, fructose and sorbitol, fructans and galactooligosaccharides, induced IBS-like symptoms. These studies also showed that dietary restriction of short-chain carbohydrates was associated with symptom improvement in some people with IBS.

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. 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). 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.

The FODMAP concept was first published in 2005 as part of a hypothesis paper. 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.

The low FODMAP diet was originally developed by a research team at Monash University in Melbourne, Australia. 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. Monash University also established a rigorous food analysis program to measure the FODMAP content of a wide selection of Australian and international foods. 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.

As a result of this program of research and FODMAP food analysis, a comprehensive and accurate database now exists describing the FODMAP content of food; scientists now understand the mechanism by which the diet works and there is sound evidence indicating that a low FODMAP diet improves symptom control in approximately three out of every four people with IBS and other FGIDs (such as simple bloating).

FGID

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.

Absorption

Poor absorption of most FODMAP carbohydrates is common to everyone. Any FODMAPs that are not absorbed in the small intestine pass into the large intestine, where bacteria ferment them. The resultant production of gas potentially results in bloating and flatulence. Most individuals do not suffer significant symptoms but some may suffer the symptoms of IBS. Restriction of FODMAP intake in the latter group has been found to result in improvement of symptoms.

Fructose malabsorption and lactose intolerance may produce IBS symptoms through the same mechanism but, unlike with other FODMAPs, poor absorption is found only in a minority of people. 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.

Sources in the diet

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

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

Fructans, galactans and polyols (mandatory restriction)

Sources of fructans

Sources of fructans include wheat (although some wheat strains such as spelt contain lower amounts), rye, barley, onion, garlic, Jerusalem and globe artichoke, asparagus, beetroot, chicory, dandelion leaves, leek, radicchio, the white part of spring onion, broccoli, brussels sprouts, cabbage, fennel and prebiotics such as fructooligosaccharides (FOS), oligofructose and inulin.

Sources of galactans

Pulses and beans are the main dietary sources (though green beans, tofu and tempeh contain comparatively low amounts).

Sources of polyols

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.

Fructose and lactose (discretionary restriction)

Sources of fructose

See: Foods with high fructose content

Sources of lactose

See: Avoiding lactose-containing products

Low-FODMAP diet suggested foods

Below are low-FODMAP foods categorized by group according to the Monash University "Low FODMAP Diet".

• Vegetables: Alfalfa, bean sprouts, green beans, bok choy, capsicum (bell pepper), carrot, chives, fresh herbs, choy sum, cucumber, lettuce, tomato, zucchini
• Fruits: Banana, orange, mandarin, grapes, melon
• Protein: Meats, fish, chicken, tofu, tempeh
• Dairy: Lactose-free milk, lactose-free yoghurts, hard cheese
• Breads and cereals: Gluten-free bread and sourdough spelt bread, rice bubbles, oats, gluten-free pasta, rice, quinoa
• Biscuits (cookies) and snacks: Gluten-free biscuits, rice cakes, corn thins
• Nuts and seeds: Almonds (<10 nuts), pumpkin seeds
• Beverage options: water, coffee or tea

Other sources confirm the suitability of these and suggest some additional foods.

Effectiveness and nutritional adequacy

Evidence from randomized trials indicates that a low FODMAP diet can help to treat irritable bowel syndrome in adults and in children. A comprehensive systematic review and meta-analysis supports the efficacy of this diet in the treatment of functional gastrointestinal symptoms of IBS although the evidence is less good for constipation.

There is only a little evidence of effectiveness in treating functional symptoms in inflammatory bowel disease from small studies which are susceptible to bias.

In common with other defined diets, the low FODMAP diet can be impractical to follow and risks imposing an undue financial burden and worsening malnutrition.

See also

• Carbohydrate metabolism

External links

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