For all the recent interest in whole grains and the South Beach Diet, Americans certainly aren’t getting any thinner. The causes of being overweight or obese go beyond fast food (although that certainly plays a role). Even in our wealthy country, access to food—especially to healthy food—can be a problem. In hundreds of rural "food desert" counties, residents must drive farther than 10 miles to reach a supermarket. Cities such as Baltimore and Albany, N.Y., offer spotty access to healthy food items, while Detroit doesn’t have a major grocery chain within city limits. Meanwhile, vacant urban land that could be used for agriculture sits idle.