The term 'Oligosaccharides' includes two types of FODMAPs - fructans and galacto-oligosaccharides (GOS). We have had many requests from the public over the years asking us to separate these FODMAPs, so in our recent app update we did just that, to make it easier for you to find the foods you are sensitive to.
Fructans and GOS were originally grouped together because they are very similar, these diagrams will help explain.
Fructans are chains of fructose sugars joined together with glucose at the end.
In order to absorb fructans, we need to break the sugars down into single sugars (monosaccharides). But, we can’t. Humans do not produce any enzymes that can break down the bonds between these sugars, so the fructans move through the gut completely unabsorbed. When the fructans meet bacteria in the large intestine, they are fermented which produces gases. In healthy people this causes a bit of wind and is part of normal, healthy digestion. In IBS, where the gut is hypersensitive and motility disturbances are common, this results in bloating, abdominal discomfort and altered motility.
The same occurs with GOS. GOS are chains of galactose sugars joined together with glucose at the end.
Again there is no human enzyme capable of breaking down the bonds between the galactose sugars, so they move through the gut unabsorbed. Poor absorption of GOS leads to symptoms in IBS patients.
So these oligosaccharides (oligos) always pass through the gut and escape digestion. They have beneficial effects whereby they encourage the growth of good bacteria and act as prebiotics, but if you have IBS you might notice symptoms after ingesting foods rich in the oligos.
Now that these two FODMAPs are separated, it is important for you to test your tolerance to each e.g. trying legumes (GOS) as well as garlic (fructan). Remember, the long term FODMAP diet is a modified version of the diet, individualised for you based on your reactions to food reintroductions. Keep trying new foods. Within each FODMAP subgroup you may tolerate some foods, but not others.