...Vegetarianism is more than just not eating meat, said Roberta Anding, a registered dietitian at Baylor College of Medicine and Texas Children's Hospital and a spokesperson for the dietetic association.

"It's really embracing more of that plant-based lifestyle and having enough variety in your diet that you can be well-nourished," Anding said. "You can be unbelievably well-nourished on a vegetarian diet if you choose your foods wisely and appropriately." 

Lilian Cheung, director of health promotion and communication at Harvard School of Public Health's Department of Nutrition, agreed. Teens who abstain from eating animal-based foods but who take in refined and sugary foods such as French fries and sodas are not doing themselves any favors, she said.

Eating a variety of vegetables and fruits of all colors and eating the purest form possible is vital in these diets, Cheung said. Beans, legumes, nuts, tofu and seeds all are excellent protein sources, said Cheung, who said veganism and vegetarianism are becoming more mainstream among young people.

"I think the reason why veganism is getting more and more popular is there are more celebrities like President Clinton," embracing the lifestyle, said Cheung, editorial director of the department's nutrition website, The Nutrition Source...