In a statement issued on the opening of the annual summit of the World Health Organisation (Who), Belgian professor Olivier de Schutter called for efforts to launch negotiations on a global pact to tackle the obesity epidemic.
"Unhealthy diets are now a greater threat to global health than tobacco.
"Just as the world came together to regulate the risks of tobacco, a bold framework convention on adequate diets must now be agreed," he said.
De Schutter, who has held his post of special rapporteur on the right to food since 2008 and earlier headed the Paris-based International Federation of Human Rights, reports to the UN Human Rights Council in Geneva.
In 2005, a UN convention on tobacco control aimed at reducing deaths and health problems caused by the product went into force after long negotiations under the umbrella of the Who.