Over the last decade, milk has become a bit controversial. Some people say it's a necessary and nutritious food, vital for healthy bones, but others say it can cause cancer and lead to an early death. So, who's right? And why are we drinking it anyway? [Intro music] Milk is the basis of every mammal's diet after birth, when our digestive systems are immature and small. Basically, it's power food to kick-start our bodies and help us grow. Milk is rich in fat, vitamins, minerals, and milk-sugar: lactose.