Mexico’s government has tried to encourage millions more of its obese citizens to cut down on their soda intake before they reach such a crisis. In January 2014, it introduced a tax of one peso a liter, or about 10 percent, on sugary-sweetened drinks. In doing so, it turned the nation into the ground zero of a global battle between healthcare lobbyists and big soda. As legislators from London to Lima look at similar measures, both sides have been analyzing Mexico’s obesity problems and the effects of its soda tax on them.