Only in the mind of a child — or a member of Congress with a frozen pizza manufacturer in his district — could pizza sauce be considered a vegetable. Yet it was that very idea, combined with some outdated nutritional information, that pushed Congress to forbid the U.S. Department of Agriculture from requiring schools to improve the meals they serve our children.

The rules that currently govern school meals were established 15 years ago, and what we know about nutrition has changed since then. We know, for example, that dark vegetables — be they red or green — are better than the lighter ones. Where fruits and veggies are concerned, as long as they haven’t been fried or soaked in sugar, more is better. We better understand the problems that can be caused by trans and saturated fats, and we know that whole grains pack a nutritional power that’s hard to beat. And some of the things that we thought we knew aren’t so true.

Earlier this year, the USDA decided it was time to bring its school lunch and breakfast programs into line with current nutritional science. In the process, it decided that pizza sauce is not a vegetable, a move that sent some food manufacturers into a tizzy. Some were worried by limits placed on the number of servings of potatoes and other proposed changes. Opponents fought back, arguing, in part, that healthier meals would cost the food program more.

They said that pizza should be considered a vegetable because of all that nutrient-dense tomato sauce on top. Yet nutritionists point out that to get enough sauce to pack the same nutritional value as a standard serving of fresh tomatoes you’d have to drown the pizza in sauce, serving up to 1⁄2 cup per slice. There are other problems, as well: Those fresh tomatoes are salt free; the sauce is loaded with the stuff.

Americans are right to be worried about their weight these days, and they’re right to be worried about their children’s weight. Yet the old rules make it far more difficult to teach children what’s good for them and to give them practice eating it. In this case, Congress did us no favors by saying yes to the pizza and fries.