Homelessness is a global issue, but how and why do people become homeless? It's the question author David Geliebter sought to answer when writing Underbelly, which takes a closer look at the homeless population in Palm Beach, Florida. Dr. Oz talks with David about his book and what we can do to help the homeless.

Underbelly chronicles the lives of 21 homeless people in an area of Florida typically known for wealth and privilege. David says homeless people think and feel just like everyone else—except they are nameless, faceless and voiceless. "I really felt their story needed to be told," he says.

Many of the people he talked to became homeless after escaping into drugs, alcohol and other addictions. "There are a lot of things that predispose you to being addicted," David says. "One of them is being depressed or having a mental illness."

David says people tend to brush aside the homeless and assume they are going to be that way forever, but Underbelly represents why it's wrong to stereotype them that way. "There are people who cope better and people who cope worse with the stresses of life," David says. "It's just not identified by one type of person or one situation."