FODMAPs™

How do FODMAPs trigger IBS symptoms?

Because FODMAPs can be malabsorbed by the small intestine they can reach the large intestine where the bacteria live. These bacteria can rapidly ferment these sugars to produce gases - carbon dioxide, hydrogen and methane. This can produce ‘wind’ or flatulence. The large intestine is well designed for this ‘fermentation process’ and so fermentation here does not cause great discomfort for people. We can call this ‘healthy fermentation’. The situation, however, is very different for people with Irritable Bowel Syndrome (IBS).

In individuals who suffer from IBS, the cause may be the movement of the bacteria into the small intestine means that fermentation can proceed higher up the gut. The small intestine is not designed for fermentation. The small intestine has a much smaller diameter and the production of gases in this small space can result in great pain and discomfort for people. We can call this ‘unhealthy fermentation’. In addition, people with IBS have greater ‘visceral sensitivity’ (which means that they are more sensitive to the expansion of their intestine by these gases). The normal “healthy fermentation” in the large bowel can in these situations cause distressing symptoms. Other consequences of this ‘unhealthy fermentation process’ include bloating, distension and altered bowel habit (that can range from diarrhea to constipation).

Who malabsorbs FODMAP sugars?

We are all different and not everyone will malabsorb all of these FODMAP sugars.

Here are some interesting facts:

Fructose
– Fructose is a monosaccharide (single molecule sugar). The absorption of fructose in the small intestine relies on the activity of special ‘sugar transporters’ that are located in the wall of the small intestine. Most people can absorb fructose (however around 30% of healthy individuals and 40% of individuals who suffer from IBS, will malabsorb fructose). We do not fully understand why this is the case, and research in this area is currently underway.
Lactose
– Lactose is a disaccharide (two molecule sugar - made up of one Galactose and one Glucose molecule). The absorption of lactose requires this disaccharide to be divided into the two separate molecules by an enzyme (called lactase) followed by the absorption of the single sugar units. The enzyme lactase is located in the wall of the small intestine. If you lack this enzyme then you will malabsorb lactose. The levels of lactase enzyme can vary depending on factors such as ethnicity (with people of Asian descent often having low levels of lactase) and also the presence of certain gut disorders.
Sugar polyols (eg. sorbtiol, mannitol)
– The sugar polyols are absorbed across the small intestine without the use of special enzymes. In people with IBS most research had been conducted on the polyol called sorbitol. Research looking at mannitol is currently underway.
Fructans
– Humans do not have the enzymes to break down fructans, so all fructans will be ‘malabsorbed’ in the small intestine. Bacteria can rapidly break down fructans.
Galactans
– Humans do not have the enzymes to break down galactans, so all galactans will be ‘malabsorbed’ in the small intestine. Bacteria can rapidly break down galactans.

Fructose and lactose are the most common FODMAP sugars. Currently, fructose and lactose are the only FODMAP sugars that are tested routinely for malabsorption.

FODMAP and FODMAPs are trademarks of Dr Sue Shepherd.