Obesity, once a problem chiefly in the world’s richest countries, is increasingly prevalent among poor and less educated women in developing nations, a study released on Wednesday said.

The findings from 37 developing countries including China, Brazil and India, revealed a major shift in the populations hardest hit by obesity, researchers said.

In the past, experts found excess weight was a problem mainly for people living in wealthy nations such as the United States, Britain, Germany and Japan. The poorer residents of those countries typically were heavier than richer ones.

The opposite was true in developing countries, where only the richest were overweight and the poor could not get enough food to become fat.

The new study by researchers in the United States and Brazil, found poor and less educated women around the world now struggling with obesity, which raises the risks of heart disease, stroke, diabetes, some cancers and other health problems.

In many poorer nations, obesity has become more prevalent than malnutrition, said Barry Popkin, a nutritionist at the University of North Carolina and one of the study’s authors.

“Worldwide, the burden of obesity increasingly rests on the poor and less educated, even in many developing nations we never thought of as having an obesity problem,” Popkin said.

Popkin and colleagues at the University of North Carolina worked with researchers at the University of Sao Paolo in Brazil to analyze data from nearly 149,000 women between ages 20 and 49.

The findings, published in the International Journal of Obesity, were released at a conference on obesity sponsored by Time magazine and ABC News.

Problems with weight among the poor occur in nations with gross national product above $2,500 per capita, the study said.

Less labor-intensive work, which burns fewer calories, and lower food prices likely are major drivers of the rising obesity rates, Popkin said. Other contributors may be a lack of knowledge about health and trouble acquiring more expensive, healthier foods.

The study was funded by the U.S. National Institutes of Health.