Fructose Malabsorption and FODMAP’s

The management of Irritable Bowel Syndrome

by Julie Albrecht, A.P.D.

Irritable bowel syndrome (IBS), is a functional gut disorder which affects up to 15 % of the community(1). IBS is a term which is used to define a variety of dysfunctions, which are characterised by chronic abdominal pain, bloating and alternation in bowel habits – constipation / diarrhoea, in the absence of any organic cause. There may also be bowel urgency or the feeling of incomplete evacuation, gastro -oesophageal reflux, and depression. The exact cause of IBS is unknown. Theories highlight the interaction between the gastrointestinal tract and the brain, along with abnormalities in gut flora and or the immune system.

Fructose is a short chain carbohydrate found widely in our diet as a free hexose in fruits, disaccharide in sucrose and in a polymerized form – frutans(1). In the free form, fructose has a limited absorption in the small intestine(1). The average daily intake of fructose ranges from 11 – 54 g, with up one half of the population being unable to completely absorb a 25g load(1). Fructans are not hydrolysed or absorbed in the small intestine. It is the malabsorption of free fructose and fructans that may induce gastrointestinal symptoms in individuals with a functional gut disorder(1).

The acronym FODMAPs - Fermentable Oligosaccharides, Disaccharides and Monosaccharides, is used to define an unrelated group of short chain carbohydrate and sugar alcohols. These include fructose, lactose, polyols – sorbitol, xylitol and fructans and galactans(1). These all have a similar fate in the small bowel and colon(1). In the individual, fermentable short chain carbohydrates like fructose and lactose may be malabsorbed, polyols are generally poorly absorbed and fructans and galactans are always poorly absorbed in all individuals(1).

The physiological consequences of the malabsorption of FODMAP’s include an increased osmotic load, the provision of a substrate for rapid bacterial fermentation, changes in gastrointestinal motility, and the promotion of mucosal biofilm and the alteration of the bacterial profile(1).

The prevalence of fructose or fructose sorbitol malabsorption in the healthy population appears to be similar to that found in the populations with functional gut disorder(1). The difference between the two populations lies in the frequency of the induction of symptoms, highlighting the change in luminal conditions (induced by fructose) being the determinant rather than the malabsorption(1).

Research undertaking dietary intervention encompassing the exclusion of FODMAP’s, has been applied to patients with IBS(2). An evaluation of the outcome of this intervention revealed that 85 % of patients who adhered to the dietary intervention, had a marked and a sustained improvement in all abdominal symptoms (abdominal pain, gas, bloating, diarrhoea and constipation)(2). Of patients who adhered to the diet less than 50% of the time, 36% had a significant improvement in symptoms, particularly gas and abdominal pain(2).

This research reveals the potential the malabsorption of fructose and fructans act as contributing factors in the development of symptoms in patients with IBS. It highlights the opportunity to improve gastrointestinal symptoms and quality of life through dietary change.

Unfavourable Foods – Fructose & Fructans(2)

References:

1. P.R. Gibson, E. Newnham, J.S. Barrett, S.J. Shepherd and J.G. Muir. Review article: Fructose malabsorption and the bigger picture. Aliment Pharmacology and Therapeutics. 2007; 25: 349 – 363.

2. S.J. Shepherd, P.R. Gibson. Fructose malabsorption and symptoms of irritable bowel syndrome: guidelines for effective dietary management. 2006; 106: 1631 -1639.