An elementary school in Ottawa is limiting students to one slice of pizza each at its weekly pizza lunches, citing a Ministry of Education policy on school nutrition.

A parent of a student at Convent Glen Catholic School in Orléans emailed CBC about the change last week, saying that in past years students had been allowed to order multiple slices.

The reason given for the restriction? Two slices exceed the ministry's limit for fat content.

The parent declined to be interviewed by CBC because of concerns about the family's ongoing relationship with the school.

Through a board spokesperson, the school principal also declined to be interviewed. But the Ottawa Catholic School Board confirmed the policy in an email.

"Considering the ministry's guidelines, the school council and school administration agreed that one slice of pizza is a reasonable approach for their community," wrote board spokesperson Mardi de Kemp.

Province's nutrition rules in place since 2011

The Ontario government brought in new rules to restrict the sale of junk food in schools in 2011.

The rules apply to cafeterias as well as fundraisers that take place on school property. That means school staff and parent councils, in addition to commercial kitchen operators, must navigate the complex policy.

That policy divides food and drinks into three categories based on nutritional data per serving: "sell most," "sell less," and "not permitted for sale."

Those in the "sell most" category are the healthiest options and must comprise 80 per cent of the food offered for sale at a given event. Foods in the "sell less" category can make up the remaining 20 per cent, while the unhealthiest foods, such as candy and chocolate, can't be sold at all.

Pizza is a puzzle

Many schools that offer pizza lunches have coped with the new rules by serving pizza that fits the "sell most" nutritional criteria.

Some pizza restaurant chains have developed special menus that meet the guidelines, using ingredients such as reduced-fat cheese and whole wheat crusts.

Schools can offer up treats 10 times a year for special events like bake sales. (Holly Caruk/CBC) Schools that want to sell unhealthier pizzas must offer students a choice of at least four other healthier, "sell most" options at the same event. However, they can seek an exemption to the nutrition rules for a special event. Schools are permitted only 10 such exemptions per year — typically not enough for a regular lunch program, especially if the school runs other events, such as fun fairs or bake sales.

Province doesn't dictate portion sizes

Several school councils contacted by CBC Ottawa confirmed their schools allow students more than one slice at their pizza lunches.

They'll be relieved to hear the province is OK with that.

"(The policy) provides guidelines to boards on the admissible nutritional contents, including fat content, of a serving size that can be packaged and sold as one 'meal' in schools," said ministry spokesman Derek Luk in an email. "The policy does not restrict the number of servings per child."

Minister of Education Mitzie Hunter also weighed in with an emailed statement, saying the province's nutrition standards for schools "make sure that the food and beverages sold in schools contribute to students' healthy growth and development, without restricting the number of servings per child."

Restricting portion sizes on pizza days is a mistake, according to dietitian Anna Aylett, She argues that children develop a healthier relationship with food when they're allowed to choose their own portion sizes. (Susan Burgess)

Let them eat pizza: dietitian

Not only is limiting servings unnecessary under the guidelines, it could do more harm than good, according to an Ottawa dietitian.

"I don't remember the last time I ate just one slice of pizza," said Anna Aylett, a registered dietitian who works with children and their families at CHEO's Centre for Healthy Active Living. "If someone told me I could only have one, I might really want three, four, five slices of pizza, because you told me I can only have one."

In other words, restricting the food now might make a child more likely to gorge later when given the opportunity. Some children might also develop feelings of shame and guilt around eating fun foods, Aylett said, which also disrupt healthy eating habits.

The ministry guidelines are good for controlling what gets served, but kids should decide how much of it to eat, Aylett said — even if it's a greasy deep-dish pizza. Although if her own child wanted more than two slices, she'd ask them to dip into their own piggy bank to pay.

"If we start cutting hot dogs in half or allowing just one slice of pizza, I think we're overstepping," she said. "We're starting to take the fun out."