For years, health advocates have urged the public to read the ingredients and ignore the marketing. For years, consumers have ignored the health advocates.

But lo! It looks as if they’re finally listening.

Food purchases are less driven these days by what’s written on the front of the box than what’s listed as ingredients, said Andrew Mandzy, director of strategic insights at Nielsen. Some consumers aren’t even reading so much as they are counting: About 61 percent said that the shorter the ingredients’ list, the healthier the product.

Health professionals are happy to see the shift. “The overall trend of a more-educated consumer is excellent,” said Sharon Allison-Ottey, doctor, health educator, and author of “Is That Fried Chicken Worth It?” “Just being aware of what you’re eating leads you to eating less.”

Front-of-package claims such as “low-fat” and “excellent source of vitamin C” are starting to lose their magical powers, Nielsen data show. Sales of items marked for lower fat content are down 1.2 percent in dollar value over the past five years. For “fat-free,” sales are down 2.7 percent.

One claim, at least, seems to still work: “natural,” an unregulated and therefore meaningless term. Sales for such products are up 4.2 percent.

But Nielsen also created a separate category with its own, narrower criteria. For that category, market researchers took a closer look at ingredients, store placement (is it in the “Natural” aisle?), and the rest of the brand. Anything USDA-certified organic, for example, was in; anything with genetically modified organisms or artificial or synthetic ingredients was out. The growth in that narrower category was nearly triple the growth in the broader one, at 11.2 percent.

But as consumers pay closer attention to ingredients, they may be getting a little too zealous, avoiding some that are largely harmless. Sales of products blaring that they are gluten-free are up 11.8 percent over the past five years, and soy-free sales are up 29.8 percent. But health professionals don’t recommend that average Americans cut either ingredient.

Among the healthiest foods are fresh fruits and vegetables. Growth in sales of these items from the perimeter of the supermarket outpaces those from the center of the store, Mandzy said.