A 40 per cent reduction in sugar-sweetened beverages over five years could prevent more than a million cases of weight-related disease, a new study says.

Cutting the amount of sugar in sweetened drinks by 40 per cent could prevent 300,000 cases of diabetes and one million cases of obesity, research suggests.

The study, published in The Lancet Diabetes and Endocrinology journal, states that this reduction in sugar-sweetened beverages (SSBs) - including fruit juices - over five years could lead to 500,000 fewer cases of people being overweight, one million fewer cases of obesity, and 300,000 fewer instances of Type 2 diabetes, over two decades.

Some fizzy drinks contain around 10 teaspoons of added sugar.

In 2014, the World Health Organisation (WHO) said people should cut their sugar intake in half if they wanted to reap health benefits.

It said sugars should make up less than 5 per cent of total energy intake per day for adults and children.

The Lancet study was led by Professor Graham MacGregor, chairman of the Action on Sugar group, who said its action plan needed to be backed up by a Government-funded but independent nutrition agency "which can set mandatory targets with robust enforcement".

He added: "In support of this, the British Retail Consortium is now calling for regulated sugar, fat and salt reduction targets.

In the study, researchers used data to calculate the level of SSB consumption and its contribution to energy intake in the UK population.

They then estimated how the reduction would affect body weight per person, and overall results for the adult population.

These calculations showed that a 40 per cent reduction in sugars added to SSBs over five years - provided they are not replaced by artificial sweeteners - would lead to an average 1.2kg reduction in adult body weight.

This in turn would prevent more than a million cases of disease.

The predicted impact was found to be greater in adolescents, young adults and individuals from low-income families who consume more SSBs, the research said.

But researchers said the gradual sugar content reduction would not affect sales or product prices.

Professor Stephen O'Rahilly, from the University of Cambridge, said: "This is a purely theoretical study and there are many assumptions made which reduce confidence in the statements regarding the precise extent of the health benefit."

He added that, while the evidence surrounding the health dangers of sugar are "hard to argue with", the same does not necessarily apply for replacement sweeteners.

"The best quality evidence currently available indicates that artificial sweeteners do not significantly contribute to human obesity or diabetes," he said.