Soda taxes are in the news. The UK government announced a new tax that will be proportional to the amount of sugars in drinks and that it hopes will help curb childhood obesity. Philadelphia's new mayor, Jim Kenney, is trying to pass a sugary drink tax, but is presenting it in the more palatable way of increasing revenue for education, libraries and parks in poverty stricken neighborhoods. Mexico enacted a soda tax in 2014, and it seems to work: Sales of sugary drinks dropped by as much as 12 percent. Berkeley, California approved a sugary drink tax in 2014, and San Francisco and Oakland are considering putting one on the ballots this fall election.
While added sugar is on the things-to-eat-less-of list, the added sugar in drinks is a specific target for health experts and governments. Anti-soda is a growing movement. Liquid or solid, sugar has 4 calories per gram, but most weight loss and healthy lifestyle programs target the liquid form of sugar first.
The Western diet contains lots of sugar, and while sugar is added to many foods, most of the added sugar hides in drinks – soda, sports drinks, energy drinks, flavored milk and fruit juices – and that might be enough to explain why sugary drinks are linked so tightly with obesity.
But studies have shown that there is something distinctive about getting calories in liquid form. Solid sugars affect satiety, while studies have demonstrated that liquid sugar doesn’t suppress appetite -- sugary drinks’ calories are just added, and the meals eaten with the them will be just as large, if not larger. When it comes to type 2 diabetes, obesity is a well known major risk factor, but several studies have suggested that sugary drinks are an independent risk factor for the widespread disease.
So is it just that liquid sugar lends itself to overconsumption, or does sugar in liquid form pose an especially tough burden on our body’s metabolism?
Sugary drinks, glucose intolerance and diabetes
A study in the Journal of Nutrition followed 564 Canadian kids aged 10-12 years for 2 years, assessed their liquid and solid added sugar intake, and looked at their fasting sugar, fasting insulin, insulin resistance and weight. The kids were healthy but at risk for obesity because at least one of their parents was obese, and about 40 percent of the kids were already overweight or obese when the study began.
The results show that sugar in liquid rather than in solid form was associated with higher levels of fasting glucose and fasting insulin, and also with greater insulin resistance. Insulin sensitivity, which was assessed with an index that used the kids’ oral glucose tolerance tests, was reduced with higher dietary intakes of sugary drinks. Insulin resistance grew with higher intakes of liquid sugar.
The way our body deals with sugar is a good predictor of type 2 diabetes risk. High levels of fasting glucose and fasting insulin show that the cells are not responding properly to insulin (insulin, secreted in reaction to food, normally pushes sugar into cells, and its levels during fasting are supposed to be low.) Impaired glucose tolerance is a pre-diabetic state, and untreated, may develop into full-blown type 2 diabetes. So the results of this study suggest that liquid -- rather than solid -- added sugar predisposes to diabetes, independent of obesity rates, which in this study’s 2-year follow up were no different between the groups.
So while too much sugar is a problem, this study adds to the body of evidence that demonstrates that sugary drinks are especially harmful; their high availability, low price and effective marketing make them an important contributor not only to obesity, but also to pre-diabetes in kids. Mind you, type 2 diabetes used to be called adult onset diabetes, and was unheard of in pediatric practice several decades ago. Nowadays, it is estimated that 1 in 4 teens has pre-diabetes or diabetes.