Marla Lopez is 54 but eats like a toddler.

She has never eaten a piece of fruit or tried a green vegetable. For as long as she can remember, her daily diet has consisted primarily of three kinds of foods: milk (and ice cream); white breads (including crackers, tortillas and pancakes); and potatoes (including chips and French fries).

Sometimes she'll also eat bacon.

READ MORE: Is Picky Eating a Medical Condition?

Lopez said her picky eating started as an infant. She would gag on her baby food. Foods that most people would consider mouth-watering - an omelet or a sandwich - are now repulsive to her. Touching spaghetti is also out of the question.

"Good Morning America" correspondent Linsey Davis went shopping with Lopez at a Fairway Market in New York City. Not much made it into the cart.

Asked whether she'd consider items in the produce aisle, Lopez said, "When I look at this, I don't see food."

Her favorite food is potato chips, she said, adding that they were "so salty, and fresh, and potato-y. I love them."

Lopez, a mother herself, acknowledged that her preferred foods were limited but added, "I do love what I eat and enjoy it."

As for whether her eating habits are more a simple desire for junk food than a real disorder, Lopez said, "I've heard that all my life, all my life. It's really embarrassing."

Nancy Zucker, the director of the Center for Eating Disorders at Duke University Medical Center in Durham, N.C., says Lopez is not alone.

"We don't quite understand what adult picky eating is … but what we do know is that there is a real biological struggle going on that's not all in their heads," said Zucker, who studies picky eaters.

Lopez is often compelled to hide her eating habits when she's at parties. She'll say she already ate, or she'll just carry around a drink.

Despite her carb-heavy, vegetable-free diet, Lopez says she is healthy.

"My cholesterol is 174," she said, by itself no cause for alarm. "And I eat a bag of fries each day, and that's my main staple."