Cans and bottles of sugar-sweetened colas, lemonade and fruit drinks, which many people think can be drunk with impunity, are today implicated as a major cause of obesity and linked to a rise in diabetes by scientists in the United States.
A new study, published in the Journal of the American Medical Association, says the problem may be that the drinks fail to make people feel full in spite of being loaded with calories.
Caroline Apovian, a US nutrition expert writing a commentary on the study, says that the human race has probably not yet evolved to cope with these sugar-loaded drinks.
"A better mechanism for weight gain could not have developed ... Liquid calories are a relatively new addition to the human diet - perhaps the human satiety circuit has not yet adapted to register these calories for what they are," she writes.
A single can may contain 40 to 50g of sugar. Somebody who drinks one can a day could put on 15lb over a year, she writes. She advises doctors in the US to tell their overweight patients to cut down.
"Reducing sugar-sweetened beverage consumption may be the best single opportunity to curb the obesity epidemic."
She also calls on the US government to change its stance on sugar in the diet. Pressure from the US, which was batting on behalf of its food and sugar industries, led to the World Health Organisation this year backing off from its original intention to recommend a specific limit of 10% of calories in a healthy diet coming from sugar.
The US government rejected a scientific report commissioned by the WHO which criticised the food industry for "heavy marketing practices of energy-dense, micronutrient poor food", claiming it was not evidence-based.
The study published today "should help convince the US government that further changes in health policy are needed", says Dr Apovian of the Boston Medical Centre and Boston University School of Medicine in Massachusetts.
The authors of the study, Matthias Schulze of the department of nutrition at Harvard School of Public Health and colleagues, point out that soft drink consumption in the US increased in adults by 61% from 1977 to 1997 and more than doubled in children and adolescents between the late 1970s and mid-1990s.
They studied the sugar-sweetened soft drink consumption of a large cohort of young and middle-aged female nurses. The diabetes analysis included over 90,000 women who were free of diabetes and other chronic diseases at the starting point in 1991, while the weight change analysis included over 50,000 women.
They found weight gain was highest among women who increased their sugar-sweetened soft drink consumption from one drink or less a week to one drink or more every day. Drinking fruit punches - not pure fruit juice but sweetened fruit drinks and cordials - also caused weight gain. Drinking either the sugar-sweetened beverages or the fruit drinks daily was associated with a higher risk of diabetes.
The UK is following closely the obesity pattern of the US, although a few years behind. The International Obesity Task Force said yesterday that sweetened soft drinks were potentially as serious a problem in this country as they are across the Atlantic, even though diet colas without the sugar content are said to be growing in popularity.
"The problem we have is that we still have high sugar drinks being marketed to children in Britain as if the industry was unaware there was a problem," said spokesman Neville Rigby.
Richard Laming of the British Soft Drinks Association said that the study only showed weight gain among women who increased the amount of drinks they consumed without taking more exercise.
