LONDON If Barry Popkin had his way, sugary drinks would be taxed like cigarettes, and the levy would go up and up until societies were weaned off them and stopped piling on weight.
A nutrition expert who has advised the U.S. government and health policy makers around the world, Popkin says the epidemic of obesity and weight gain sweeping the globe could be slowed dramatically if people revised the mantra "you are what you eat" to include "you are what you drink."
Reviving a taste for water could cut between 300 and 600 calories a day from the diet of an average American or Mexican and almost as much from the intake of many Europeans, he says.
"Depending on the country you live in, we now have between 10 and 25 percent of all calories consumed in sugary or caloric beverages," Popkin, a professor of nutrition at the University of North Carolina, told Reuters during a visit to Europe.
"This change has been phenomenal, particularly in the past 25 years. It's not the sole cause of the global obesity problem, but it's the thing we can change with the least affect on people's food intake."
Data on weight gain and rising obesity levels leave little room for doubt that fat is threatening to overwhelm health care systems and government health budgets around the world.
A report released on Wednesday said one in three American adults is obese, while a 2008 study by Popkin on China suggested obesity levels there are also rising rapidly, with more than a quarter of the population overweight or obese.
The number of people with diabetes - one of the major chronic diseases caused by excess weight - is already reaching epidemic levels, with an estimated 180 million people suffering from it around the world.
Diabetes cases are forecast to triple in the United States in the next 25 years to 44 million with the costs of caring for them rising to $336 billion a year.
Popkin reckons there are now around 25 countries where more than half of adults are overweight or obese and in many rich countries as well as some middle-income nations like South Africa, Mexico and Egypt, the rate is between 60 and 70 percent.
The World Health Organization said in October that being overweight has now overtaken being underweight among the world's leading causes of death.
Popkin, who has studied diet in many countries in Europe, Asia, the Middle East and the United States say the shift away from water to sugary drinks could be responsible for between a third and two thirds of the weight gain in the past 30 years.
"The obesity and weight issue is now bearing heavily on us and our health care costs," he said. "And it's getting worse."
But Popkin says efforts to tackle rising weight levels are focused too much on promoting exercise and healthier eating, and ignore the huge impact of calorie-laden drinks like juices, alcohol, fizzy soda and high fat, sugary milkshakes.
"Activity is not the solution - you can't run off a Coke or an ice-cream cone or candy bar very easily - it takes a lot of exercise to offset an extra hundred calories," he said.
The nutrition expert says the basic problem is that when people shift from drinking water or unsweetened tea and coffee to sugary drinks and juices, they don't cut their food intake.
But since the biological mechanisms controlling thirst and hunger are separate, he says reducing calories by changing people's drinking tastes - rather than chasing elusive ways to cut their eating - is a viable way of fighting fat.
Popkin acknowledges it would take time - probably a decade - to change the world's tastes away from sugary drinks, but he said policy makers should look at tobacco as an example and use taxes as their weapon.
Ever higher taxes on smoking and policies to ban smoking in public paces are helping cut tobacco use in Europe - and studies show a positive effect on cancer rates.
"I'd like a system where sugary drinks were taxed the most, diet drinks less and water not at all," Popkin said. "If that tax added even 15 or 20 percent to the cost, it would have a significant effect on weaning society off sugary drinks."