Lactose is the sugar found in milk (human or animal milk) and hence other diary products. It can be found in a surprising number of products including biscuits and pizza. The enzyme (protein) lactase is produced in the small intestine of our bodies and breaks down lactose into glucose, a more simple form of sugar which can be absorbed and used by the body. After the age of about two years old our bodies naturally produce less lactase, some children (although this is rare) are born without the ability to product lactase at all, other people may experience symptoms in older age. However, where there is a lactase deficiency lactose will not be absorbed properly in the intestine and can ferment leading to the production of gases such as methane.
Common symptoms of lactose intolerance which can develop hours or even days after taking the food, are not life threatening but can include bloating, cramps, colic in babies, diarrhea or nausea and can subsequently lead to weight loss and malnutrition. Symptoms vary widely as each individual will be able to tolerate varying amounts of lactose – for instance the condition is significantly more common in certain ethnic and racial populations such as African or Asian groups, where milk has been less traditionally part of a typical adult diet.