Elizabeth Nyikako, 16, a senior at Whitney Young High School in Chicago, used to buy a Coke or a Twix candy bar from school vending machines, but no more. Now she gets bottled water and granola bars.

Shone Talbert, 16, a junior at Hirsch Metro High School in the city, liked to get Butterfingers, potato chips and soft drinks from the machines. But now he buys them on his way to school.

That's because last year Chicago public schools revamped what was offered in the machines. Soft drinks were booted out, and water, sports drinks and juice were offered instead. Granola bars and baked chips replaced candy bars and fried chips.

Food for thought is taking on a new meaning as students across the nation begin a new school year. Chicago is just one of many school districts that have mobilized to replace high-fat, high-sugar foods and drinks with healthier choices in vending machines and cafeteria a la carte lines. Students returning to schools in cities such as Washington, D.C., will see good-for-you foods in vending machines for the first time this fall.

This year alone, 42 state legislatures have enacted or proposed measures that require or recommend nutritional guidance for schools, said Carla Plaza of Health Policy Tracking Service, which reports on state health legislation. Some set limits for elementary and middle schools but give high schools more choices. Others propose standards that would apply to all grades.

"This has been a watershed year for state legislation dealing with school nutrition," said Amy Winterfeld, a health policy analyst for the National Conference of State Legislatures. "There has been a wide range of legislation covering everything from offering healthier beverages to eliminating deep-fat frying."

Why the nationwide drive to get junk foods out of schools? Because you can't pick up a newspaper or magazine without reading about childhood obesity. About 31 percent of children ages 6 to 19 are overweight or at risk of becoming so, according to the Centers for Disease Control and Prevention.

Many students aren't happy with the change.

"What they have to offer now, none of us want," Talbert said. "It's OK to be healthy every now and then, but it shouldn't be forced on us."

But many parents, public health advocates, school administrators, food service directors and legislators think it's crucial that schools offer healthy fare.

Even some industry groups are joining the effort. Recently, the American Beverage Association recommended that beverage companies adopt voluntary restrictions on the sales of soft drinks in school vending machines. The group recommends eliminating soft drinks in elementary schools, severely restricting them in middle schools and requiring that they be only 50 percent of the choices in high school machines.

Some schools are junk food "free-for-alls," said Enid Hohn, director of the nutrition services division for Vista Unified School District in San Diego County. Hohn revamped her district's vending machines five years ago to offer healthier fare. The district replaced chips, candy and sodas with granola bars, dried fruit, beef jerky, nuts, cut-up fruit, shaker salads, vegetables with ranch dressing, tuna packs with crackers, water bottles, milk and fruit juice.

Hohn visits other school districts nationally to discuss nutritional changes. In many, students can get candy or soft drinks from the vending machines and buy doughnuts, sodas, chips and cookies from school stores, Hohn says. Plus, school fundraising groups hawk everything from cookie dough to gargantuan candy bars, she said.

The traditional school lunch programs need to operate on a level playing field, Hohn said. "If I'm selling healthy stuff in the lunch line, and the kids can walk 10 feet and buy three fresh-baked cookies for a buck from the school store, that's where they will spend their money," she said. "It's ridiculous."

In fact, the rules governing school foods are fairly complex.

Traditional school breakfast and lunch programs are regulated by the U.S. Department of Agriculture. The foods in vending machines and school stores — sometimes called "competitive foods" because they compete with the meal programs — are not regulated by the agency.

And the USDA's guidelines for foods of minimal nutritional value in school a la carte lines haven't been updated for years.

A recent survey supports what Hohn has observed about the abundance of "junk" food. A Pennsylvania State University study of 228 school-food service directors in that state showed that high-schoolers are surrounded by high-fat, high-sugar foods, and not just in vending machines.

The survey found that hamburgers, pizza and sandwiches are top sellers in a la carte lines.

But some industry groups argue that the sale of commercial foods at school is not the problem.

Dan Mindus, a senior analyst with the Center for Consumer Freedom, a Washington, D.C.-based group supported by the restaurant and food industry, said, "The best thing schools can do about childhood obesity is to get kids moving in gym class."