FOR JESSICA ZIMMERMAN, a fifth-grader at Northside Elementary School in Middleton, Wis., lunch is the most trying meal of the day. Because of a rare genetic condition that makes protein act like poison inside her body, Jessica can’t eat most of the things fifth-graders eat: no hot dogs, no chicken strips, no eggs, milk or cheese. If she were to eat any of these foods, an amino acid called phenylalanine would collect in her bloodstream and travel straight to her brain, where it would cause her to lose concentration on her studies and play havoc with her emotions.
Instead, Jessica follows a prescribed diet stricter than any vegan’s. A typical packed lunch includes a sandwich of artificial cheese on homemade, protein-free bread, a piece of fruit and mineral water. But the really awful part is what she must drink: a foul-smelling, milky-white beverage that provides virtually all of her dietary protein. Blended fresh daily by her mother, Ann, the beverage is a cocktail of amino acids specially designed for people with Jessica’s condition, known as phenylketonuria, or PKU. Jessica drinks this concoction three times a day, even though she hates the way it tastes and how it makes her breath smell.
At school, kids sometimes teased her for drinking “baby formula,” and now she refuses to drink it there, opting to wait until she gets home. But without her mid-day dose of amino acids, Jessica’s mind drifts in afternoon classes.
“Controlling Jessica’s phenylalanine levels poses constant dilemmas no kid should have to face,” Ann Zimmerman says. “A small Rice Krispie treat or a small order of French fries is a rare delight, which requires Jessie to be extra diligent that day. She never gets a day off. Not on her birthday, not on Halloween, not on Christmas.”
It’s unfair, Ann thinks, that food could be so cruel.
IN A LABORATORY-CUM-KITCHEN in Babcock Hall, Kathy Nelson, a researcher at the Wisconsin Center for Dairy Research, measures ingredients on a digital scale before throwing them in a mixing bowl. She’s making a batch of strawberry pudding, her favorite in a line of foods she designed for Jessica Zimmerman and others with PKU. These items may soon be the first protein-rich foods Jessica ever eats.
Nelson’s foods contain a secret ingredient: a unique protein derived from whey, the liquid byproduct of cheesemaking.
For the 15,000 people in the United States with PKU, protein is usually a problem because their bodies lack the enzyme responsible for breaking down phenylalanine, one of the 20 major amino acids that form proteins. All of the proteins we eat in everyday foods contain phenylalanine, and because of that, diet is a chore for people with PKU. A little phenylalanine is essential. But excess amounts can stay in the body indefinitely and interfere with brain function. Too much phenylalanine leads to “an inability to concentrate and focus,” says Sally Gleason, a nutritional counselor and case manager who works with individuals with PKU at UW-Madison’s Waisman Center, one of the nation’s premier centers for PKU research. “They also face emotional problems and depression.” The only solution for Jessica is to heavily supplement her diet with the amino-acid shake, which is specially formulated to exclude phenylalanine.
In the late 1990s, however, CALS food scientist Mark Etzel found another option: a protein known as glycomacropeptide. GMP turns out to be the only dietary protein in nature that doesn’t contain phenylalanine. And the only place you can find GMP is in whey, which is produced when milk curdles to form cheese curds. Working for the WCDR, a largely farmer-funded organization dedicated to supporting the dairy industry, Etzel developed a method to isolate and purify large quantities of GMP from whey, some 22 billion pounds of which are generated by Wisconsin’s cheese plants every year. In fact, for every one pound of cheese, dairy plants end up with nine pounds of whey.