Obesity, undernutrition and climate change are the biggest threats to the world population, driven by profit motives and policy inertia, top international experts warn.

The Lancet's Commission on Obesity has called for a binding plan and trillions of dollars to thwart the dangers of unsustainable agricultural production, transport, urban design and land use.

The commission's stark message comes a week after the EAT-Lancet Commission warned humans must radically change their diets to avert catastrophic damage to the planet.

Almost two in three Australian adults and one in four children are overweight or obese. Credit:Simone De Peak

A $1 billion fund and action strategies targeting food policy and production are needed urgently to support health, the environment and economic wellbeing, according to the report published on Monday.