By the BBC's Emma Jane Kirby BBC correspondent in Geneva

The World Heart Federation is warning that obesity will overtake tobacco smoking as the biggest cause of heart disease unless the current trend of unhealthy lifestyles stops.

At least a billion people across the globe are now extremely overweight, putting a massive strain on worldwide healthcare systems.

Obesity - which can cause heart disease, strokes and diabetes - is on the increase across the globe.

According to the World Heart Federation, an estimated 22 million children under the age of five are now severely overweight.

Nearly one in three children in the United States between the ages of five and 14 are obese, compared to one in six 30 years ago.

The World Heart Foundation says diet and lifestyles need to change

But obesity is not a condition which solely affects the western world.

Increasingly, low and middle income countries are suffering from the condition, often due to a change in their diets, as they substitute fibre intake for a much higher consumption of saturated fats and sugar.

In Beijing, for example, one in five children of school age are now obese.

The World Heart Federation says obesity can also be blamed for spiralling health costs.

The US spends almost a tenth of its national healthcare budget on overweight patients, and in western countries as much as 2.8% of total sick care costs can be attributed to obesity.