Obesity experts say that the poor economy threatens to worsen Americans' already bulging waistlines. Unhealthy food often happens to be the cheapest. But there are healthy cheap foods.

Dr. Adam Drewnowski, who directs the University of Washington Center for Public Health Nutrition and is pushing for the federal government to put more affordability into the calculation when it issues new dietary guidelines next year.

When Drewnowski examined what the Agriculture Department calls a "thrifty food plan" for healthy eating, he found it takes between 9 and 16 hours a week to purchase, prepare and cook, as opposed to the 5 hours normally spent on this by working families.

On his list, carrots trump peppers, and apples trump strawberries in terms of best nutrition for the price.