What a first lady, a chain store and others are doing to try to make fresh fruits and vegetables more available in poor communities. Nothing’s ever as simple as we’d like it to be. A case in point: Policies that simply increase access to supermarkets may not get people to choose an apple over ice cream, a recent study reported. Changing people’s eating habits is difficult, in other words. One reason is money. Healthful foods such as fruits and vegetables, whole grains, lean meats and dairy, can often be pricey. For the cost of a couple of peaches, a person...