MEXICO CITY — The contentious negotiations over the fate of the North American Free Trade Agreement have veered into one of the world’s most pressing health issues: fighting obesity.

Urged on by big American food and soft-drink companies, the Trump administration is using the trade talks with Mexico and Canada to try to limit the ability of the pact’s three members — including the United States — to warn consumers about the dangers of junk food, according to confidential documents outlining the American position.

The American stance reflects an intensifying battle among trade officials, the food industry and governments across the hemisphere. The administration’s position could help insulate American manufacturers from pressure to include more explicit labels on their products, both abroad and in the United States. But health officials worry that it would also impede international efforts to contain a growing health crisis.