We all know that exercise works wonders for your waistline, but what about your brain? According to psychiatrist Dr. Michael Miller, exercise is great for the brain—and what's good for the brain is good for your entire body. Bob talks to Dr. Miller, the editor-in-chief of the Harvard Mental Health newsletter, about the mental health benefits of physical activity.

From your mood to your emotional well-being, Dr. Miller says "it all starts with the brain." Without exercise, he says your brain simply isn't as healthy, and the health of your entire body can potentially suffer. For example, exercising has been shown to alleviate symptoms of depression. So by boosting your mood through exercise, you can create a cycle of healthier behaviors.

Dr. Miller says that exercise has also been shown to substantially improve your brain's health and performance. With regular exercise, your brain becomes more efficient, blood flow increases to the brain and the brain cells create more robust connections to one another. On top of that, Dr. Miller says that the latest research shows that exercise actually makes your brain grow, particularly in the parts of the brain responsible for controlling your mood and memory. "There actually is new brain cell growth in those areas," he says.

The bottom line is that you have to stay active in order to stay healthy—physically and mentally, Dr. Miller says. "[Exercise is] certainly going to improve the quality of your life," he says. "You're going to feel better, your mood is going to be better, your sense of well-being will be much improved, you'll sleep better. It'll have all sorts of benefits to make every minute of every day much more comfortable and much more pleasant."