A new study which links soft drink consumption with obesity has its detractors, writes Iva Pocock.
Drinking sugar-sweetened cola and fruit drinks every day is a sure way of putting on weight, and can greatly increase the chances of developing diabetes, according to research published by US scientists last week.
From studying more than 50,000 female nurses, the researchers found that those who drank one sugar-sweetened drink every day were likely to pile on more pounds than those who indulged only once a month.
In addition, the daily soda drinkers had a more than 80 per cent increased risk of developing Type 2 diabetes, the most common form of this chronic, and increasingly prevalent, disease.
The research has upped the ante in the battle between health activists, who are calling for a tax on soft drinks, and the sugar industry, which has lobbied against moves to encourage people to limit their sugar intake.
In a strong rebuttal of the study, which appeared in the Journal of the American Medical Association, Richard Adamson, vice-president of the American Beverage Association, described the findings as "scientifically un-sound" and "at odds with all that's known in the scientific community".
Prof Albert Flynn, professor of nutrition at University College Cork, is also sceptical of the research. "I don't think these types of studies can prove the conclusions they are drawing."
Flynn is critical of the way in which the US researchers gathered their data. One weakness, for example, was the fact that the women studied were self-reporting, he says.
"In the end, it is very difficult to show that any single food is contributing to obesity," says Flynn.
Adamson pointed out that the women who drink a lot of sodas may simply have an unhealthy lifestyle, and that many other variables may explain their increased risk of disease.
A representative of the Sugar Association, quoted in the Washington Post, suggested that any increased risk for diabetes in the study could be attributed to the weight gained, not their sugar intake. "It's not about sugar. It's about calorie imbalance," he says.
Other scientists welcomed the research as an important study which adds to recent evidence suggesting an association between increased consumption of fizzy drinks and obesity in children.
The soft drink industry loses "credibility by the day" says one academic.
"Reducing soft drink consumption may be a powerful means of addressing the obesity crisis."
One thing is certain, the non-diet sodas and fruit drinks which line shop shelves on either side of the Atlantic are laden with sugar of one sort or another. A perusal of the soft drinks found in any Irish newsagent reveals that all (except the "diet" variety) are sweetened with either sugar (known scientifically as sucrose), glucose syrup or fructose syrup.
Sucrose is actually made up of the two so-called "simple sugars" - glucose and fructose. When consumed, sugar, like all carbohydrates, boosts the blood glucose level and stimulates the body to release insulin, which ensures the glucose gets to where it's needed.
However, some carbohydrates boost blood glucose levels faster than others - the fastest have a high glycemic load, whereas slow-releasing carbohydrates have a low glycemic load.
The US researchers looked at drinks which were sweetened with either sucrose (regular sugar) or high-fructose corn syrup.
Sugar-sweetened soft drinks contribute to "a high glycemic index of the overall diet, a risk factor for diabetes in this study population", write the researchers, who say that consumption of sugar-sweetened soft drinks induces a fast and dramatic increase in both glucose and insulin concentrations.
In contrast, the researchers found that fruit juice consumption was not associated with diabetes risk in their study.
However, drinking fruit "punches", which contain just a small amount of real fruit juice and large amounts of added high-fructose corn syrup, was associated with increased diabetes risk.
One reason offered as to why women drinking lots of sodas gained more weight than those who drank them less frequently is the "low satiety" of the liquid foods.
In other words, drinking sodas or colas doesn't make you feel full, even if they are calorie-rich, so you won't adjust your other food intake accordingly.
A US nutrition expert, Caroline Apovian, who wrote a commentary on the study, advised doctors to urge their overweight patients to cut down on soft drinks.
After all, a single can may contain 40g to 50g of sugar.