Answer: A - Lactose is the primary source of energy in human breast milk. Breastmilk does also contain small amounts of fructose and oligosaccharides. The body easily breaks lactose down into glucose and galactose to provide energy to the growing brain. An enzyme called lactase is necessary for the metabolism of lactose and is present in the infant's digestive tract. Rarely is a baby born without this enzyme; therefore, lactose intolerance is rarely seen in babies. True lactose intolerance does show up after the age of weaning in some mammals, including humans.