The federal 2005 Dietary Guidelines recommend people eat two cups of fruit and two cups of vegetables per day. The guidelines recommend eating a variety of fruits and vegetables daily, selecting from all five vegetable subgroups -- dark green, orange, legumes, starchy vegetables and other vegetables several times a week.

A market basket survey was conducted at 25 supermarkets across three time periods to allow for seasonal variation in produce prices using stores selected from census tracts with a variety of income levels in Sacramento and Los Angeles.

"Public policies should examine ways to make fruits and vegetables more affordable to low-income families," the researchers concluded.

The findings are published in the Journal of the American Dietetic Association.