Low FODMAP Diet Explained

by Lucia Stansbie

You might have heard before of low FODMAP diet, but you might not be sure what exactly it is. FODMAP is short for fermentable oligo-, di-, and monosaccharide and polyols, which are short chain carbohydrates that can excessively ferment in the small intestine. Those compounds can be found in certain vegetables, fruits, fresh dairy, legumes and sweeteners.

The low FODMAP diet was formalised in Australia in 2007, and is now suggested to manage IBS (irritable bowel syndrome), as FODMAPs can aggravate the symptoms.
Low FODMAP diets can be quite restrictive and for this reason should be followed only for a limited amount of time (maximum of 6 weeks) by strict guidance from a registered nutritionist or dietician, with the aim of reintroducing the biggest possible amount of foods.

What are FODMAPs?
In a habitual diet, the total daily intake of FODMAPs ranges from 15 grams to 30 grams per day, a quantity which normally shouldn’t trigger any digestive distress. In IBS sufferers, even small amounts of FODMAPs can cause symptoms such as bloating, pain and altered bowel movements, because of their osmotic activity and high fermentability.

FODMAPS and how they can trigger IBS symptoms
• The oligosaccharides, further divided into fructans and galacto-oligosaccharide (GOS), have the longest chain length and are found naturally in wheat, rye, legumes, nuts, artichokes, onion, and garlic. There is no human enzyme capable of breaking down fructans and GOS, and, as a result they are fermented by colonic bacteria, which can be a significant contributor to bloating, abdominal pain, and excessive flatus in people affected by IBS.
• The disaccharide FODMAP is lactose, the sugar found in milk products which is broken down by the enzyme lactase. Lactase activity can be reduced in certain ethnic backgrounds, such as Asian and Mediterranean, with increasing age, and during periods of intestinal inflammation such as in active IBD (Irritable bowel disease) and IBS.
• The monosaccharide FODMAP is fructose, a single sugar found in some fruits such as apples, pears, watermelon, mango, as well as in honey and some vegetables including sugar snap peas. Fructose is also a component of sweeteners used in processed foods, such as high fructose corn syrup. Being a small molecule, fructose has a high osmotic effect and ability to draw water into the bowel lumen, resulting in distension of the small intestine which can translate in pain, bloating and altered motility.
• The polyols are mannitol and sorbitol, found in apples, pears, stone fruits, cauliflower, mushrooms, and snow peas. These polyols in addition to xylitol, isomalt, are also used as artificial sweeteners in sugar-free produce. Like fructose, polyols have osmotic on the bowel lumen.

After the two- to six-week restrictive phase where all FODMAPs are eliminated, with the guidance of a registered nutritionist some foods should be reintroduced into the diet. This is to avoid possible nutritional imbalance and to improve nutritional adequacy, with the final aim to eliminate only the real “trigger” foods (adapted low FODMAP).

The Pros
Low FODMAP diet is generally used to manage IBS (irritable bowel syndrome) and SIBO (small intestine bacterial overgrowth). Between 50% to 80% IBS sufferers experience symptom relief as soon as starting a low FODMAP diet. Symptoms improvement are still experienced in 61% at short-term follow-up, and 57% at long-term follow-up of patients following an adapted low FODMAP.
The pro of this diet is to be able to effectively manage IBS symptoms, providing symptomatic relief. Eliminating the FODMAPs will then allow to reintroduce foods one by one to then identity the real triggers and create a long lasting plan that should allow the patient to experience little or no symptoms in the long run.

The cons
Like other restrictive diets, the low-FODMAP diet carries risks of nutritional deficiencies and of fostering disordered eating in individuals with a history or predisposition to those.
Nutritional deficiencies:
A self prescribed or excessively long elimination of all FODMAP foods can lead to:
• The exclusion of carbohydrates rich in fructans may lead to a reduction in carbohydrate, fiber, and iron intake. Carbohydrates are the main source of energy for our body cells, while fiber is essential for microbiota variety and diversity. A constant lack of fiber can also lead to constipation. Iron is involved in many metabolic functions, and a deficiency may lead to fatigue or anaemia.
• The lower amount of kcalories may lead to an excessive weight loss.
• The exclusion of several types of vegetables may lead to a reduction in antioxidants intake, such as flavonoids, carotenoids, and vitamin C and anthocyanins. Antioxidants are key to overall health, being involved in many cellular metabolic functions as well reducing inflammation.
• The exclusion of dairy products may foster calcium deficiency, both because they are the main food source and because lactose acts as a promoter of its absorption.

Impact on the microbiota
FODMAPs fructans and galacto-oligosaccharides have prebiotic actions and their restriction may lead to a reduction in beneficial bacteria, especially the SCFA (short chain fatty acid) producing ones. Studies have shown that a diet very low in FODMAPs carried out over 3/4 weeks, is associated with a reduction in the abundance of SCFA producing bacterias in feces. If dysbiosis is the cause of IBS, a strict low-FODMAP can exacerbate the condition.

Recommendation
A low FODMAP diet is a great therapeutic tool to manage IBS related symptoms, but it should be followed only for a limited time. It is vital that a registered nutritionist or dietician is in charge of the low FODMAP plan, and supervises the patient both during the restriction and reintroduction phase. This is absolutely not a self prescribed diet, as only a trained professional can avoid nutritional deficiencies and microbiota alteration typical of a poor managed low FODMAP diet.

References
Barrett, J., 2017. How to institute the low-FODMAP diet. Journal of Gastroenterology and Hepatology, 32, pp.8-10.
Bellini, M., Tonarelli, S., Nagy, A., Pancetti, A., Costa, F., Ricchiuti, A., de Bortoli, N., Mosca, M., Marchi, S. and Rossi, A., 2020. Low FODMAP Diet: Evidence, Doubts, and Hopes. Nutrients, 12(1), p.148.
David, L., Maurice, C., Carmody, R., Gootenberg, D., Button, J., Wolfe, B., Ling, A., Devlin, A., Varma, Y., Fischbach, M., Biddinger, S., Dutton, R. and Turnbaugh, P., 2013. Diet rapidly and reproducibly alters the human gut microbiome. Nature, 505(7484), pp.559-563.
de Roest, R., Dobbs, B., Chapman, B., Batman, B., O’Brien, L., Leeper, J., Hebblethwaite, C. and Gearry, R., 2013. The low FODMAP diet improves gastrointestinal symptoms in patients with irritable bowel syndrome: a prospective study. International Journal of Clinical Practice, 67(9), pp.895-903.
Gearry, R., Skidmore, P., O’Brien, L., Wilkinson, T. and Nanayakkara, W., 2016. Efficacy of the low FODMAP diet for treating irritable bowel syndrome: the evidence to date. Clinical and Experimental Gastroenterology, p.131.
Harvie, R., Chisholm, A., Bisanz, J., Burton, J., Herbison, P., Schultz, K. and Schultz, M., 2017. Long-term irritable bowel syndrome symptom control with reintroduction of selected FODMAPs. World Journal of Gastroenterology, 23(25), p.4632.
Hill, Peta et al.,2017. Controversies and Recent Developments of the Low-FODMAP Diet. Gastroenterology & hepatology, 13(1), pp.36-45.
O’Keeffe, M., Jansen, C., Martin, L., Williams, M., Seamark, L., Staudacher, H., Irving, P., Whelan, K. and Lomer, M., 2017. Long-term impact of the low-FODMAP diet on gastrointestinal symptoms, dietary intake, patient acceptability, and healthcare utilization in irritable bowel syndrome. Neurogastroenterology & Motility, 30(1), p.e13154.