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.
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 new study in the Journal of Nutrition followed 564 Canadian kids aged 10-12 years at the start of the study for two years, assessing their liquid and solid added sugar intake, and looking 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 prediabetic 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 two-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 prediabetes 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 prediabetes or diabetes.
Full disclosure: I'm vice president of product development for Herbal Water, where we make organic herb-infused waters that have zero calories and no sugar or artificial ingredients. I'm also a pediatrician and have been promoting good nutrition and healthy lifestyle for many years.