This marks the first time ever that senior policymakers from the countries within the WHO European region have gathered for such an event.
The aim is to move towards the adoption of a European Charter on Counteracting Obesity.
The conference marks growing recognition that effective, comprehensive action involving all stakeholders is needed.
For example, half of all adults and one in five children in the WHO European Region are overweight. A third of these are already obese and numbers are accelerating.
The WHO reckons that the epidemic causes 1 million deaths a year and seriously hampers economic development. "No country has yet managed to bring it under control," said the organisation.
Indeed, no single strategy appears to be working. A recently published two-year study from the UK's University of Sussex for example argued that improvements in health education are not sufficient to tackle the crisis in Europe, and recommended a raft of initiatives.
"The UK and other European governments need to take several steps to make it much easier for citizens to have healthier diets and lifestyles," said project leader Professor Erik Millstone.
"A coherent set of government policies is needed, or the problem will only get worse."
This then is the aim of the Istanbul conference. But a number of controversial issues must be addressed before an agreement is reached. Restricting food marketing and advertising to children and young people for example has divided the food industry, regulators and health campaigners.
While the UK's Food and Drink Federation insists that consumers don't want a 9pm watershed on food advertising to children, consumer group Which? insists that "advertising has a proven effect on children's food choices."
The Istanbul event has been organised by the WHO regional office for Europe and hosted by the ministry of health of Turkey. The European Commission is the principal international partner.
Other organisations such as the Food and Agriculture Organisation of the United Nations (FAO), the United Nations Childrens Fund (UNICEF), the International Labour Organisation (ILO), the Council of Europe, the World Bank and other international and regional agencies, as well as nongovernmental organisations, will take part.