BAKERSFIELD, Calif. — Dark chocolate is in. So, too, is beef jerky. And full-fat ice cream? You bet.

Driven by fast-changing definitions of what is healthy to eat, people are turning to foods they shunned just a couple of years ago. Studies now suggest that not all fat, for example, necessarily contributes to weight gain or heart problems. That has left companies scrambling to push some foods that they thought had long passed their popularity peak — and health advocates wondering what went wrong.

Under the new thinking, not all fat is bad, and neither are all salty foods. A stigma among the public remains for sugar substitutes, but less so for cane sugar, at least in moderation. And all of those attributes are weighed against qualities like simplicity and taste.

“I think the risk-reward equation has changed,” said Steve French, a managing partner at the Natural Marketing Institute, a research firm, said.