A government-sponsored junk food ban in schools across Mexico took effect on Saturday, officials said, as the country tries to tackle one of the world’s worst obesity and diabetes epidemics.

The health guidelines, first published last fall, take a direct shot at salty and sweet processed products that have become a staple for generations of Mexican schoolchildren, such as sugary fruit drinks, packaged chips, artificial pork rinds and soy-encased, chili-flavored peanuts.

Announcing that the…