It's the cinemas that the nutrition adviser Susan Jebb worries about most. People do not generally buy cola in supersized buckets, but in the cinema we do, along with vast tubs of popcorn. A large 16oz cup of cola contains 16 teaspoons of sugar, according to the Harvard School of Public Health. That is a potentially considerable problem for the waistline.
"Because it is in liquid form, the evidence is that [a sugary drink] doesn't fill you up," says Jebb. "They seem to supplement our food rather than substitute. If people have 400 calories of Jelly Babies or 400 calories of drink, they may eat less after the Jelly Babies, but they don't decrease their calories at all after the drink."
Sugary drinks are increasingly indicted as partly responsible for the expanding girth of western nations. Jebb, head of diet and population health at the Medical Research Council Human Nutrition Research unit in Cambridge, is excited by New York mayor Michael Bloomberg's plan to ban sugary drinks being sold in containers larger than 16oz.
There is plenty of evidence that soft drinks are a contributory factor to the obesity epidemic, says Dr Mike Rayner, of the department of public health at Oxford University. Most soft drinks have no more nutritional value than water. "We are proposing a tax on soft drinks rather than anything else," says Rayner, who co-authored a paper published by the British Medical Journal which proposed levying a 20% tax on sugary drinks.
"It is food you can easily cut down on without serious consequences," says Rayner. "All the alternatives are slightly better than sugary drinks. Some fruit juices have as much sugar, but they do have other things going for them, such as vitamin C and maybe a bit of fibre. Milk [in dairy-based drinks] is a good source of calcium."
Some other countries have already taken this road or are thinking about it. France has a higher tax on sweetened drinks, although Rayner says it is very low, and Denmark levies more duty on products with high saturated fat.
The Oxford paper has had little reaction yet from either government or public health bodies but, Rayner says, "this is a campaign that has begun".
Jebb herself was a joint author of a paper last December that modelled what would happen if a 10% tax were brought in on sugary drinks, but she is not completely convinced it is the way to go. "It does suggest that if you put the price of something up, it brings consumption down – but there is no real evidence, and food costs are relatively little," she said.
Meanwhile, the soft drinks industry says there is not a problem. Manufacturers have cut calories and people can choose healthier drinks if they want to. On the publication of the latest soft drinks industry responsibility report last week, Richard Laming, of the British Soft Drinks Association, said: "The soft drinks industry has a long track record of acting responsibly in order to deal with issues of public concern.
"Providing a wide range of enjoyable drinks, including 100% natural drinks as well as diet, low calorie and no-added-sugar drinks, means that people can choose the ones that suit their own diets best.
"What has happened is that the proportion of the market made up of drinks with no added sugar is now 60%, up from only 30% 20 years ago. This is a major contribution to limiting calorie intake."
guardian.co.uk © Guardian News and Media 2012