"The bottom line for obesity is that we are eating too much of everything, not only sugar."

A sugar tax alone will not reduce obesity

"Related to sugar and calories, an interesting “natural experiment” occurred in Cuba during the 1990s. After the Soviet Union’s collapse, Cubans’ life turned difficult and in the diet the proportion of energy from sugar cane increased. 

Still, obesity, diabetes, and heart disease decreased, because total calories were reduced. The bottom line for obesity is that we are eating too much of everything, not only sugar. Pizzas, fries and salty pastries do not include much sugar, still they can make one obese and their saturated fat increases risk for vascular disease. A sugar tax may be a good start in the prevention of obesity, but on the other hand may give a misguiding signal that shunning sugar corrects everything. Maybe a calorie tax on food items would be a better idea."