The former Iowa science teacher and McDonald's Corp "brand ambassador," who preached the virtues of walking and near-daily french fries in presentations to youth, is no longer visiting U.S. schools, the fast-food chain said on Friday.

The program presented by John Cisna, author of the book "My McDonald's Diet: How I lost 37 pounds in 90 days and became a viral media sensation," was sharply criticized by teachers, parents and public health advocates who accused McDonald's of trying to hook youngsters on unhealthy food.

Cisna's program included a documentary and discussion guide edited by McDonald's, which hired him in 2015 and provides him with a stipend for time and travel related to his speaking engagements. His presentations came shortly after the new CEO of the 60-year-old chain had begun working to transform McDonald's into a "modern, progressive burger company."

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"As our brand ambassador, John is focused on internal and local community events, and he is not appearing at schools," McDonald's said in a statement. A McDonald's spokeswoman declined to elaborate.

While some of Cisna's materials can be used for internal and community events, the company said, "none of these materials are currently used in schools."