But after hearing Toni Branner's lecture on nutrition at her dance class two years ago, Armstrong, 17, switched to homemade ham and cheese sandwiches and snacks of trail mix and dried fruit.

"I got scared after hearing what I was doing to my body," she said. Armstrong didn't fear weight gain -- the small-boned ballerina has always been slim. But she lacked stamina and often skipped practice because of strep throat. Branner told her it was because of those Big Macs.

Branner, a Charlotte exercise physiologist, speaks regularly to teenage athletes. Her message is simple: Eating well means performing well. She recently gave Ashley's class at the Weir Dance studio in Matthews a pep talk before the biggest dance competition of the year.

To make her point about the perils of Big Macs, she made a Crisco burger: She spooned Crisco onto a bun to show how much fat is in a standard McDonald's meal -- quarter pounder with cheese, medium fries and medium milkshake.

The girls said "ew" when Branner was finished. The meal, she said, has 58 grams of fat, about 90 percent of the daily recommended intake.

Then she unspooled bunches of sugar packets taped to a can of Sunkist and a packet of M&Ms to show how much sugar each contains. For the soda, it's 13 packets, and the candy, eight. Just look at the grams of sugar and divide by four, and that's the number of sugar packets in your favorite junk food, she told them.

Branner promotes a whole foods diet abundant in raw fruits and vegetables (nine to 13 each day), whole grains and protein-packed foods such as hummus and peanut butter. While it's not a new concept, Branner thinks teens need to be reminded that the payoffs of eating healthy outweigh the pleasures of junk food.

She decided to write a book, "The Care and Feeding of a Dancer," after witnessing the poor eating habits of dancers at her daughter Jenna's dance competitions a few years ago.

"You'll see kids eating chicken nuggets and [drinking] Mountain Dew, and then as soon as they're offstage, they'll grab their asthma inhalers," she said. "Most of the time they're just dehydrated."

Branner also wrote a guide on healthy eating for athletes and, most recently, for soccer players.

She explains how all athletes produce an excess of what's called oxidative stress that can damage organs and muscles and lead to diseases such as cancer. That's why athletes, especially, should eat an abundance of antioxidants in fruits and vegetables to neutralize the effects.

Branner told the dancers that bad food would make them sluggish dancers, and it could make them sick adults.

"The same things we do to prevent heart disease are the things we do to be better athletes. It's not easy, but it is simple," Branner said.

It's not about weight

Absent from Branner's message is emphasis on weight. That's a welcome omission for a roomful of dancers of all body types, from lithe to buxom. Although dance teachers nowadays are more open to dancers of all body types, eating disorders are still prevalent in dance academies, Branner said.

The dancers Branner has trained say they don't diet -- they just eat healthfully and are able to maintain a natural weight.

They do let themselves splurge on occasion. For Ashley, that means hushpuppies or warm steak fries with cold ranch sauce. Taylor Hoverman, 16, another Weir dancer, treats herself to ice cream every other week.

But most of the time Taylor eats fruit when she craves something sweet.

The girls also say their concentration, mood and self-esteem have improved after following Branner's tips. Being healthy has allowed them to handle an intense lifestyle that includes 15 to 20 hours of dance practice a week, plus school and homework.

Sometimes their friends who don't dance try to get them to eat junk food, but the dancers' peer pressure to eat well is stronger, they say.

"We bully each other. 'If you're getting a soda, you're leaving the table,'" said Taylor. "When we have slumber parties, you don't find junk food."