Scientists say new evidence links certain chemicals to the development of obesity. About 2,500 international experts are attending the 16th European Congress on Obesity in Geneva. Lisa Schlein reports for VOA the participants are assessing the latest research from basic science to practical prevention programs and medical treatment for obesity.

About half of the world's population is overweight or obese. And, scientists and policy makers say the problem is growing and causing people to die prematurely because of obesity-related illnesses such as diabetes and heart disease.

Scientists at the conference presented results of several studies in animals that show that exposure to certain substances during development, either in the womb or during infancy, may contribute to obesity later in life.

These chemicals are used to make products such as baby bottles, the lining of food cans and some plastic food wraps and containers.

The scientists agree eating too much and exercising too little remain the major causes of obesity. But, they cite new evidence that mice exposed to endocrine disrupting chemicals during pregnancy produce offspring that became fat as adults.

Bruce Blumberg is a developmental biologist at the University of California at Irvine. He is looking at the link between obesity and another class of chemical compounds called Tributylin. This is used as a fungicide and treatment for industrial water supplies, wells and in various kinds of plastics found in water pipes.

"Exposure to very tiny levels of tributylin is able to alter metabolism such that animals and presumably people get fatter," said Bruce Blumberg. "We know from other studies that drugs, which target the same receptor make people who take the drug get fat. We have also shown in our animal models that when you expose mice in utero to tributylin and then never again, that these animals will get about 15 percent fatter at adulthood. A single pre-natal exposure alters the physiology of the exposed animals such that they will become fat later in life."

The scientists say this information has the potential to change how people view and treat obesity. If these findings are proven to be true in humans, they say then the focus in tackling obesity must change.

They say there should be a shift from adult weight loss to the prevention of weight gain during development by reducing the exposure to certain substances.

Neuro-endocrinologist at Tufts University in the United States, Beverly Rubin, says people can do many things to limit exposure to hormone-altering chemicals.

"If we consider that the majority of exposure is by ingestion, it is pretty easy to stay away from polycarbonate plastics and to use fresh foods instead of canned foods and try to avoid the sources that we know contain this Bisphenol A leaching," she said. "And I think it is most important if we are talking about pregnant mothers because our studies and the studies of many other laboratories show that the most concern is during development, during early development, during fetal development."

The scientists agree obesity is caused by multiple factors and must be treated in multiple ways. They say new research shows obese patients can achieve long-term weight loss without drugs using a low-cost approach involving innovative intensive therapy.