Much of the four-day meeting, which began on Wednesday, will be devoted to obesity's consequences, which include cardiovascular disease, respiratory problems, diabetes, depression and cancers.
A leading expert said that obesity, which affects more than 300 million people and an alarming number of children, should be recognised and treated as a disease with deadly complications.
"Obesity is not an aesthetic problem. It is a very complex problem tightly connected to diabetes, atherosclerosis [blocked arteries] and other major health problems and causes of death. It has to be treated and confronted seriously," Professor Constantine Tsigos, chairman of gathering, said ahead of the meeting.
"The emphasis has been put on the complications to increase the awareness of obesity as a disease and a serious condition with many risks associated with it," said Tsigos.
Up to 8 percent of healthcare costs in some Western countries are attributable to obesity and related problems.
It is a leading cause of preventable death, so shedding excess weight is not just about looking good.
In European countries, rates have soared by 10%-50% in the past decade.
In Japan, the rate has doubled since 1982, and in the United States, the percentage of young overweight people has tripled in 25 years.
Tsigos said prevention efforts must be geared to the young because excess weight in children is linked to early markers for metabolic syndrome - a collection of health risks that increase the odds of developing heart disease, stroke and diabetes.