Isomaltose
Isomaltose is a sugar that nobody adds to anything. It is a disaccharide — two glucose units joined by an alpha-1,6 bond — and it forms naturally when starch is broken down, because that alpha-1,6 link is the one found at the branch points of amylopectin. It turns up in honey, in beer and in glucose and starch syrups as a by-product of hydrolysis, and it forms in your own gut during starch digestion.
It is roughly half as sweet as sucrose and is split by the enzyme isomaltase in the small intestine. It appears in this section because it is a sugar, not because it is a sweetener anyone reaches for: there is no jar of it, and no ingredients list names it.
Three similar-sounding things, told apart
Most people arriving at this page are looking for one of the other two.
- Isomaltose — this page. A naturally occurring glucose–glucose disaccharide. Not an additive, no E number, not sold as an ingredient.
- Isomalt (E 953) — a sugar alcohol manufactured from sucrose and authorised in Great Britain as a sweetener. It is what most sugar-free boiled sweets are made of, and what pastry chefs use for blown and pulled sugar work because it resists crystallising and browning. See our entry on E953 - isomalt.
- Isomaltulose — a glucose–fructose disaccharide sold as Palatinose. A slowly digested sugar authorised as a novel food rather than an additive.
Where it comes from
Isomaltose is a marker of incomplete starch hydrolysis. When starch is broken down — by malting, by industrial enzymes making glucose syrup, or by your own digestive enzymes — the straight alpha-1,4 chains are cleaved readily, but the alpha-1,6 branch points need a different enzyme. What survives that step includes isomaltose.
That is why it shows up in beer and sake, in honey (where bees' enzymes rearrange nectar sugars), and in commercial glucose syrups. It is measured in food-composition work as an indicator of how far a starch hydrolysis has gone, rather than tracked as a nutrient in its own right.
Nutrition and safety
Isomaltose has no E number and does not appear in the FSA Register of Food Additive Authorisations, because it is not a food additive. It is a carbohydrate, and it is assessed the way sugars are: as a source of energy and as part of total and free sugars intake. No acceptable daily intake applies.
As a glucose-based disaccharide it is digested to glucose and raises blood glucose accordingly, and it counts toward carbohydrate intake like any other sugar. Because it is never present alone, there is no meaningful per-100 g figure to give for it — the sugars that matter in a diet are the ones on the label of what you are actually eating. See White Sugar (Granulated) and Honey for foods with real composition data.
There is a rare inherited condition, congenital sucrase-isomaltase deficiency, in which the enzyme that splits this bond is missing or reduced, causing bloating and diarrhoea after starchy and sugary foods. It is uncommon and is diagnosed clinically rather than by avoiding any one sugar.