A street vendor sells sweet snacks in Mexico City in 2016. Several states are pushing to ban the sale of junk food and soda to children to improve the population’s nutrition levels.

A street vendor sells sweet snacks in Mexico City, Tuesday, July 5, 2016. A study published on Tuesday shows that Mexico’s 8-percent tax on high-calorie snacks has been successful in reducing junk food purchases, but only by a small amount and only among poor and middle-class households. (AP Photo/Eduardo Verdugo)