WASHINGTON - Pregnant women, mothers and children who get federal assistance with their grocery bills will now be able to buy more whole-grain foods, yogurt, fish, fruits and vegetables.

The changes to the Special Supplemental Nutrition Program for Women, Infants, and Children, known as WIC, will go into place by next year.

The Agriculture Department announced the changes Friday as the final part of a process it began in 2007 to overhaul the program and greatly expand the number of healthy foods offered. Changes announced that year and put in place in 2009 eliminated many fruit juices from infant food packages, reduced saturated fats the program covered and made buying fruits and vegetables easier.

USDA says that overhaul will now be complete with a few more items included, such as whole grain pastas, yogurt and additional types of canned fish. The rule also newly allows fresh fruits and vegetables for older babies when mothers do not want to feed them jarred baby food.

The final rule also allows for an increase in the value of vouchers for fruits and vegetables.

USDA reaffirmed its decision not to allow white potatoes in the program, a move that the potato industry has vigorously fought.

The Agriculture Department said it will continue to eliminate white potatoes from the list of eligible foods because people already eat enough of them and vouchers aren't needed to buy more.

"The department recognizes that white potatoes can be a healthful part of one's diet," USDA wrote in the rule. "However, WIC food packages are carefully designed to address the supplemental nutritional needs of a specific population."

The potato industry responded swiftly after the rule was released, saying there is no scientific reason to exclude white potatoes, which are popular, healthy and economical for families who are already struggling to get as many nutrients as possible on a limited budget.

The WIC program provides vouchers to mothers and pregnant women who qualify for the program and specifically lists the foods they can buy. The program annually serves around 9 million people, about half of them children.

Sam Kass, director of first lady Michelle Obama's Let's Move initiative to combat childhood obesity, said WIC has been "one of our greatest success stories." He credited the program's changes to give mothers and children access to healthier foods as one of the reasons that toddler obesity has gone down in the last decade.

A study published by the Journal of the American Medical Association last week showed that obesity among children ages 2 to 5 has decreased to 8 percent from 14 percent a decade ago.

The study "gives us great hope that we're on the right path," Kass said.