Lactose is a type of sugar, naturally found in milk and dairy products. In the intestine, lactose is transformed by lactase, an enzyme, into glucose and galactose, both simpler sugars, which are used by our body for energy and various functions. Most people have difficulty digesting lactose. It is due to the normal decline of lactase activity after weaning, called non- persistence of lactase. Symptoms of lactose intolerance generally do not occur until there is less than 50% of lactase activity.
At the genetic level, the gene coding for lactase, LCT, becomes normally less active with age. In some individuals, lactase production in the intestine is sustained and they keep the ability to digest lactose after infancy, while others lose this capacity and can experience intestinal discomfort regarding the amount of lactose they consume. Lactase activity decline is more common in people of Asian, African, South American, Southern European, and Australian Aboriginal heritage than in people of Northern European (Scandinavia, the British Islands and Germany) descent.
Lactose intolerance occurs when lactose maldigestion results into one or many symptoms of intestinal discomfort such as bloating, diarrhea, and gas.
Lactose maldigesters are encouraged to consume lactose in small amounts (up to 12 g in one intake, and up to 24 g across the day, which represents one and two bowls of milk, respectively). Yogurt, which contains live bacteria that help digesting the lactose it contains, and cheeses that contain low or no lactose (cheddar, provolone, mozzarella, Grana padano, etc.) are good alternatives for lactose maldigesters.