If eating a bowl of ice cream gives you horrible gas, your body might not be manufacturing lactase. This enzyme breaks down milk sugar, or lactose, into smaller sugars that your body can digest. Normally, infants and Europeans have no trouble producing lactase, but many Asians can't and are lactose-intolerant. Even if you lack the ability to make lactase, you can still enjoy ice cream if you take a lactase pill as you dig in.

Lactase belongs to the glycoside hydrolase class of enzymes, responsible for cleaving carbohydrates as well as other molecules attached to carbohydrates. Glycoside hydrolases can cleave groups that include the elements sulfur and oxygen. Different members of the enzyme class can break down cellulose, sugar-protein complexes and other sugars and starches. Lactase belongs to the beta-galactosidase family of glycoside hydrolase enzymes. This family contains enzymes that hydrolyze, or break apart, molecules containing galactose, a sugar with six carbon atoms that is less sweet than glucose.

The sugar lactose consists of a galactose and a glucose molecule joined by a glycosidic bond. Lactase breaks this bond, allowing your body to absorb the two smaller sugars. Cells in the small intestine are primarily responsible for creating lactase. The indigestion that lactose-intolerant people experience comes from the genetic inability to create lactase. The undigested lactose passes into the large intestine where bacteria feast on it, producing byproducts such as methane. The result is an unpleasant mixture of symptoms. Fortunately for ice cream lovers, you can buy dairy products to which lactase has been added. Lactase pills are also effective.