The World Health Organization on Tuesday urged countries to impose a tax on sugary drinks to battle the growing obesity epidemic and presented new data on the beneficial health effects of such a tax.

A tax on sugary beverages raising their price 20 percent would result in a proportionate reduction in their consumption, the agency said. That would advance the fight against obesity, which has more than doubled since 1980. About half a billion adults were obese in 2014, roughly 11 percent of men and 15 percent of women.

“If governments tax products like sugary drinks, they can reduce suffering and save lives,” Dr. Douglas Bettcher, director of the W.H.O.’s Department for the Prevention of Noncommunicable Diseases, said in a statement. “They can also cut health care costs.”

Obesity began rising in rich countries several decades ago, but is now taking hold in middle-income countries like China and Mexico. Public health experts, alarmed by the trend, are studying policies that countries can enact to fight it.