Wait—you can transform your life by altering your thoughts? Believe it. Martha Beck on the mood-altering, immunity-bolstering, luck-making impact of changing your mind.

Okay, this time you're serious. You're going on a regimen that will really improve your health—not like that crash diet: You'll snarf down antioxidants; exercise moderately but consistently; balance fats, proteins, and carbs; and pay attention to the way you explain whatever happens to you.

Wait a minute. The way you explain what happens? What does that have to do with physical health? According to findings from the burgeoning field of behavioral medicine, a lot. How we think can affect physical processes as surely as diet and exercise do. For example, putting a positive spin on events in our past is associated with an enormous array of health benefits, from improved immune function to reduced stress to quicker healing, with all their emotional and physical advantages. To some degree, we may be able to literally explain away many devastating physical problems. If you want to have a healthier body, I suggest changing your mind first.