School children will find more fruits, vegetables and whole-grain products on their lunch plates under the new nutritional guidelines for the National School Lunch Program issued by the U.S. Department of Agriculture (USDA). The guidelines also seek to reduce or eliminate high contents of sodium, saturated fat and trans fats. For the first time, food and beverages sold in vending machines on campus will have to meet certain nutritional standards as well.

The newly adopted nutrition standards are largely based on recommendations by the Institute of Medicine (IOM) of the National Academies and are designed to help in the fight against childhood obesity, which is now affecting 17 percent of children living in the U.S.

Under the revised rules, all meals served in school cafeterias will have upper and lower limits of calories, which vary with each age group. Kindergarteners to fifth-graders will receive 550 to 650 calories per meal, 6th to 8th graders about 700 calories, and 12th graders up to 850 calories.

The extra costs for better nutritional quality come to about $6.8 billion over the next five years, according to government estimates. “Schools are definitely going to be challenged by the additional costs of meeting the new rules,” says Dianne Pratt-Heaver, a spokesperson for the School Nutrition Association (SNA), a non-profit organization that represents school cafeteria vendors and operators. The government will pay schools six cents per meal on top of the current rate, which is not nearly enough to cover expenses, according to the SNA. The school lunch program provides daily meals to about 32 million students, often for free or at a reduced price.

Regardless, Ms. Pratt-Heaver says, her organization approves of the new policies. The Academy of Nutrition and Dietetics (formerly known as the American Dietetic Association) has also signaled its support. “Given the realities of federal, state and local budgets, the Academy of Nutrition and Dietetics is committed to leading the creative collaborations that will be needed to implement changes in the school food program,” said Sylvia A. Escott-Stump, a Registered Dietitian and President of the Academy in an official statement by the organization.

The new regulations mark the first overhaul of the school lunch program since the 1990s and will gradually be phased in over the next three year. It was not an easy task, considering the oftentimes vehement opposition from food manufacturers, which culminated in last year’s controversy over whether pizza (or rather the tomato paste topping) should qualify as a vegetable serving. So far, it does, at least legally.

Also somewhat unresolved remains a dispute over the nutritional benefits of potatoes. The National Potato Council (NPC) has voiced strong objections to any attempts to limit servings of potatoes in school lunches, including French fries. “We still feel like the potato is downplayed in favor of other vegetables in the new guidelines,” said Mark Szymanski, a spokesperson for the NPC. “It seems the department still considers the potato a second-class vegetable.”

There is some reason for that. According to a study by the Harvard School of Public Health, which followed over 120,000 people for up to 20 years to find out what kinds of food affected their weight, potatoes were found to rank among the greatest weight boosters.

There is a very strong hypothesis that potatoes in particular lead to weight gain, says Professor Walter Willett, an Epidemiologist at Harvard and lead author of the study report. The reason is that potatoes are consumed fully cooked and rapidly broken down into sugar. Sugar is quickly absorbed into the bloodstream and eliminated by insulin, which leaves us hungry again after just a few hours. Particularly problematic, Dr. Willett says, are potatoes made into French fries and potato chips, “because they’re designed to make us overeat.”

Fried potatoes are also much higher in calorie and fat content than the steamed or baked varieties because of the oil used in the process. While one baked medium-size potato carries about 110 calories and virtually no fat, a medium-size serving of French fries has about 380 calories and 19 grams of fat.

Calories and fat, of course, are not the only issues. High levels of sodium are of equally great concern. While a medium-size potato contains about 10 mg of sodium (without added salt), a medium-size order of French fries comes with a whopping 270 mg.

Worries about sodium content have also fueled the debate over tomato paste on pizza. While tomatoes in their natural form are almost sodium-free, processed tomatoes like tomato paste, canned tomato sauce and ketchup can have over 1000 mg of sodium per serving (100g). High levels of sodium are known to cause a number of negative health effects, including heart disease and high blood pressure.

As a dietitian and grandmother of kindergarteners and gradeschoolers, I obviously support the changes the new guidelines are trying to achieve. However, much work remains to be done before all school children can receive the quality nutrition they need to grow up healthy and succeed at learning.

Timi Gustafson R.D. is a clinical dietitian and author of the book “The Healthy Diner – How to Eat Right and Still Have Fun”®, which is available on her blog, “Food and Health with Timi Gustafson R.D.” (http://www.timigustafson.com), and at amazon.com. You can follow Timi on Twitter and on Facebook.