Disaccharides are carbohydrate units (sugars, or more specifically double sugars) made up of two monosaccharides. For example, sucrose, known as table sugar, is made when a glucose and a fructose molecule join together and lactose, or milk sugar, is made when a glucose and a galactose molecule join forces. There are three common dietary disaccharides: lactose, maltose and sucrose. Lactose in particular is commonly not well tolerated in Western societies and is a component of the problematic FODMAP group. We will discuss it in more detail in the section below.
Lactose or ‘milk sugar’ is, as the name suggests, the natural sugar found in milk and dairy products. Lactose is a disaccharide made up of molecules of glucose and galactose joined together. Lactose intolerances are becoming more prevalent in Western societies and below we explain why.
Lactase is an enzyme responsible for breaking down the lactose we consume into its two simple sugars components: glucose and galactose. Both glucose and galactose, if separated into single units, can easily be absorbed through your small intestine wall into your bloodstream where it can be transported and used for energy.
Being intolerant to lactose is more common in certain ethnic minorities and is generally more prevalent as we get older. As age seems to be a contributing factor, it suggests after weaning as a baby, when we become less exposed to milk and our diets become more diverse, we are at a greater risk of producing insufficient lactase and experiencing an intolerance to lactose as a result.
As with the other FODMAPs, insufficient levels of the required enzyme mean lactose travels undigested into your large intestine where it is attacked by gut bacteria. The action of the bacteria on the lactose can produce unpleasant symptoms such as flatulence, pain, cramping and diarrhoea.
However, please bear in mind, as discussed in our FODMAP diet section, you may be lactose intolerant without necessarily being affected by the other FODMAPs.
Lactose is found in milk and other dairy products including cream and cheese. It is also found in butter and yoghurt but often in more tolerable amounts. Lactose may also be hidden in less obvious foods such as bakery products, cereals and snacks so always be sure to read the food label.
We have produced a more extensive list of specific foods containing lactose in our High FODMAP foods section. Also read our blog, [What to do if I’m lactose intolerant?] to find some useful alternatives to incorporate into your diet.
The foods regarded as FODMAPs all have one thing in common: they are commonly not digested very well, which can cause chaos in your gut. Lactose is the most common dietary disaccharide not well tolerated. In rare congenital conditions, sucrose (table sugar made from a glucose and fructose molecule joined) or maltose (found in starchy grains made from two molecules of glucose joined) may not be able to be broken down. This is a relatively rare situation and only lactose is considered to be a component of the more commonly used FODMAP framework.