Is it the potatoes or the sauce and grease on the potatoes that makes them unhealthy? (Chris Walker/Chicago Tribune)

"I lost 40 pounds without removing potatoes from my daily diet," he said.

Potatoes weren't the only foods associated with weight gain in the Harvard study. Increased servings per day of sugar-sweetened beverages, unprocessed red meats, processed meats, and sweets or desserts over four years led to an average weight gain of 1 pound, 0.95 pounds, 0.93 pounds and 0.41 pounds, respectively.

Van Horn says the study documents where people are getting their calories rather than comparing which foods cause more weight gain if consumed in equal amounts.

Calories in french fries add up, she said, but so do double burgers and several servings of soda, common fare in fast-food restaurants.

"The french fry in and of itself might be an indicator of an eating pattern that's not consistent with weight control," Van Horn said.

Rather than vilifying the potato, the message of the study should be that people are less likely to gain weight if they consume a diet filled with foods higher in fiber and water content, Van Horn said. The study showed that people who increased their daily intake of vegetables, whole grains, fruits and nuts during a four-year period lost an average of 0.22 pounds, 0.37 pounds, 0.49 pounds and 0.57 pounds, respectively.

The U.S. Department of Agriculture employed that kind of thinking in proposing that school lunch programs replace many of their potato servings with vegetables associated with weight loss. The proposal would add more fruits, vegetables, whole grains, and fat-free and low-fat milk to school meals in fall 2012 at the earliest, USDA spokeswoman Jean Daniel said.

School lunches are required to provide one-half to one cup of fruits and vegetables in any combination each day. The proposal would separate fruits and vegetables, requiring students to receive three-quarters to one cup of vegetables as well as one-half to one cup of fruits every day.

In addition, the new standard would specify certain vegetable subgroups that must be served. School lunches would have to offer weekly at least a half-cup each of dark green and orange vegetables and legumes. And starchy vegetables, including corn, lima beans, green peas and white potatoes, would be limited to one cup per week "to encourage students to try new vegetables."

The idea is to introduce students to healthier eating, proper portions and balanced diets, Daniel said.

"We're doing a really good job of eating starchy vegetables, but we're not doing a very good job as a whole of eating a variety of vegetables," Daniel said. "You will still see potatoes or corn or lima beans on the menu, but you will also see other vegetables that have nutrients children are not getting."

In Chicago Public Schools lunches, starchy vegetables have been limited to one cup a week since fall 2010, said spokesman Frank Shuftan. Tater Tots and other such products are served once a week in CPS elementary schools and available two times a week in high schools, he said.

In Joliet Public Schools District 86, potato servings of one-quarter to one-half cup are served roughly three times a week, said Bill White, food service director for the district. To prepare for the possibility of the new rules, the district will serve more vegetables such as sweet potatoes, cauliflower and spinach, he said.

It will cost more to offer a larger variety of vegetables, but White said he's mostly concerned that lunches are high quality and enjoyable.

"I don't think anyone would argue the concept that it's good to expose kids to different things," White said. "(But) the bottom line is that the kids have got to eat it for there to be any value to it. If the kids don't eat the spinach, all we're doing is meeting a national guideline."

Naperville Community Unit School District 203 started limiting potato sides about two years ago to once a week, said Barb Brown, general manager of food service provider Sodexo, and she said she didn't see any drop-off in the number of lunches sold.

Students can browse an all-you-can-eat fruits and vegetables bar with such choices as spinach, zucchini sticks, cucumber slices and salad, she said.

Daniel said there will be a learning curve for both students and school food professionals.

"Kids aren't going to like (something new) necessarily the first time they have it. It's going to take some work, but I think our children's future depends on it, and it's an important thing to do," Daniel said.

Tribune Newspapers contributed.

Kelly April is a Tribune reporter; Kristen Kridel is a freelancer.