However lactose intolerance is very common. Although it varies from country to country, "Approximately 65 percent of the human population has a reduced ability to digest lactose after infancy. ("Lactose Intolerance ")" Lactose intolerance is caused from an inability to properly digest lactose. Lactase is the enzyme that breaks down lactose and those who do not produce enouh of it are lactose intolerant. The symptoms of lactose intolerance are "abdominal pain, bloating, flatulence, nausea, and diarrhea beginning 30 minutes to 2 hours later. ("Lactose Intolerance ")"
Summary of Nutrients article on Lactose: Lactose is a carbohydrate and is made of glucose and galactose. It is found in mammal milk and provides cells with energy. Whole lactose cannot be absorbed so it is broken down. None of the functions are neccesary necause other carbohydrates can do the same. Lactose intolerance is found all over the world in infants and adults. The link to the web article is here