Step into any supermarket and you'll see thousands of labels shouting good-health claims: Whole grains! No trans fats! Essential vitamins and minerals! But figuring out what really is part of a healthy diet is getting harder and harder in these days of information overload. And it shows in the sobering statistics: 68% of Americans are overweight or obese—which is a big reason more of us are developing diseases such as diabetes, and at younger ages.