"Even though with the diet, sure we have to do a lot more work, but I can still do the same stuff as other kids," Sarah says.
That diet is a big part of Sarah's life. Because of PKU, she can't eat protein, which eliminates a lot of foods.
"I can't have nuts, vegetables. I can't eat meat, and poultry because it has too much protein and dairy, like a little carton of milk-- 8 grams of protein right there."
Protein's a problem because it contains an amino acid that doesn't act properly in PKU patients, and if diet isn't changed early on, PKU can cause mental retardation. Sarah's mom says her daughter understands she'll have to keep this diet for the rest of her life.
"It requires these kids to become very responsible at a very young age," Holly Johnson, Sarah's mother says.
And Sarah hopes her story will help these future doctors better understand how illnesses effect us. She also has a message for other kids living with PKU.
"Don't worry, they're gonna get through this. You just have to take it in specific steps, that way you don't mess up."
Sarah's doctor says most medical students remember Sarah's lecture more than any other. Something else to note-- PKU, along with several other disorders is screened for, at birth, which is by law. And cutting out protein, by the way is not easy. Sarah's parents have to buy specially made foods, that are sometimes as much as 10 times more than what we'd pay. For instance, a loaf of this specially-made bread is 10 dollars.