Studies from Britain and Mexico suggest reducing sugar in sweetened drinks or taxing it more to cut consumption can help people limit their calorie intake and lower their risk of developing diabetes, but not by much.

Two separate pieces of research published on Thursday in the British Medical Journal and The Lancet Diabetes & Endocrinology journal found that either approach can lead to a drop in calories of between about 16 and 39 a day.

The British parliament's Health Committee called last November for tough measures including a tax on sugary drinks to fight child obesity, but a spokesman for Prime Minister David Cameron said he did not agree and would propose other measures.

Graham MacGregor, who led the UK study as professor of cardiovascular medicine and chairman of the Action on Sugar campaign group, said the positive impact of calorie reduction could be dramatic across a large population over several years, even if its effect was not strong on an individual level.

A gradual reduction in drinks' sugar content over five years - without replacing it with artificial sweeteners - is the best approach, he suggested.

"Our study shows this strategy could have a profound impact on reducing energy intake from sugar-sweetened beverages and could therefore lower the risk of obesity and type 2 diabetes in the long term," he said in a statement about the findings.

His team's research used predictive modelling to assess the potential impact of a 40 percent reduction in free sugars added to drinks over five years in Britain.

The results showed this would lead to an average drop in energy intake of 38.4 calories a day by the end of the fifth year, leading to an average reduction in body weight of 1.2 kg in adults.

This, the study found, would result in some 500,0000 fewer adults being overweight and a million fewer being obese - which in turn would prevent between 274,000 and 309,000 obesity-related type 2 diabetes cases over the next two decades.

"PURELY THEORETICAL"

Stephen O'Rahilly, who is director of the metabolic research laboratories at the University of Cambridge and was not directly involved in either study, said it would be hard to argue with the broad conclusions of MacGregor's work.

It was nevertheless "a purely theoretical study", he added. "There are many assumptions made which reduce confidence in the statements regarding the precise extent of the health benefit."

In the second study in Mexico, researchers analysed the actual effect of a 10 percent tax on sugar-sweetened drinks introduced in January 2014.

They found it was associated with a 12 percent reduction in sales of taxed drinks and a 4 percent increase in purchases of untaxed drinks a year after it was implemented.

Tom Sanders, a professor of nutrition and dietetics at King's College London who was asked for independent comment, said sugar taxes can work but the effect is small.

"This study shows a fall of 36 millilitres per head per day, he said. "This is equivalent to about 1 sugar cube (16 calories), which is a drop in the caloric ocean."

Preventing obesity would need long-term reductions in total intake of around 300 to 500 calories a day, Sanders added, far greater than Mexican tax has achieved.

Richard Tiffin, director of the centre for food security at Reading University, agreed. "For the policy to be really effective at improving health, a much larger reduction in consumption is needed," he said.

"The tax is too blunt an instrument to achieve this," he said.  - Reuters