Washington, July 17 (IANS): A tax on sugary drinks that depends on the number of calories or amount of sugar per litre could help fight obesity, a study says.

A few countries like Mexico have already imposed a tax on sugary drinks. This would encourage drinks companies to offer low-calorie alternatives.

Worldwide, an estimated 1.9 billion adults are overweight, of whom 600 million are obese.

Sugary drinks are a significant contributor to obesity as they have a high sugar content and low nutritional value.

"Taxing sugary drinks isn't a new concept, but given the immediacy of the global obesity problem, it's time we got creative with how we approach it," said author of the study Dr. Evan Blecher, senior economist at the American Cancer Society.

"We could get sharper effects from taxation if we tax the dose of an ingredient, like sugar, or calories," Blecher said in Social Science & Medicine.

Blecher drew comparisons between taxing tobacco, alcohol and sugary drinks, using South Africa as a case study.

The results of tobacco tax say that taxing by the number of cigarettes is the best approach.

In case of alcohol and sugary drinks, this would mean taxing by volume.

This dose approach to taxation has been effective at reducing the consumption of alcohol in South Africa, reducing the amount of alcohol consumed in beer by 12 percent since 1998.

"This is not that different from the conceptual understanding of carbon taxes - the idea is to tax the dose of the pollutant to incentivize consumers and producers to use better technologies to reduce carbon," Blecher said.