One commonly undigested disaccharide is lactose, which consists of one glucose molecule and one galactose molecule. Lactose digestion requires an enzyme called lactase. Many people make a good supply of lactase, but at least 25% of adults are diagnosed as lactose intolerant, because their bodies do not make enough lactase. This condition is less common among young children, but often, people make less lactase as they grow up.
After learning about this sensitivity to disaccharides, Sarah mentioned to her doctor that she always ate her cereal with milk and that she felt gassy an hour or so afterward. The same thing happened after eating ice cream or pizza. This meant that at least one component of her FODMAP intolerance was lactose intolerance. She would probably be better off avoiding the D portion of FODMAPs, her doctor explained, although she could take lactase enzyme in a pill form before eating dairy foods.
Sarah tried using lactase enzyme pills, and it helped. But that did not mean that the Os, Ms, or Ps were not contributing to her condition, as well. In fact, because her stomach was upset, not just after eating cereal but also after eating pasta and other grains, the doctor suspected that she did not tolerate fructans well.
How about the M, or monosaccharides? Although most people have no problem absorbing common monosaccharides such as glucose, some people do not absorb other monosaccharides found in food. A typical example is fructose, which we can obtain from sucrose, or granulated sugar, or from fruits, such as apples or some processed foods, especially those that contain high-fructose corn syrup.
The last type of compound in FODMAPs is P, or polyols. These compounds, also called sugar alcohols, have the general formula (HOCH2[CH(OH)]nCH2OH). Three common examples of polyols are sorbitol, mannitol, and xylitol, which are added to foods, mints, and chewing gum because they taste sweet. But sorbitol, mannitol, and xylitol are not absorbed into the bloodstream and, like undigested oligosaccharides, disaccharides, and monosaccharides, they pass from the small intestine to the colon before being eliminated.