We are fat, and we’re getting fatter. Nearly a third of American children are overweight or obese. In our inner cities a prevalence of obesity of more than 50% among both children and adults is not uncommon. Too many calories in, too little energy out.

Changing behaviour is hard. Obesity has several causes, and it will take a multifaceted campaign to reverse the trend. The tobacco experience has taught us that education is not enough: regulation, litigation, and legislation are needed too. Increasing taxes on cigarettes has been the single most effective strategy in reducing smoking.

Which brings us to the sad story of the tax on sugar sweetened beverages (SSBs).

An important part of the obesity story is clearly the huge increase in consumption of SSBs: carbonated sodas, sweet teas, energy drinks, flavoured water, and sports drinks. Their use has more than doubled in recent years, and of all food types they are the single largest contributor to energy intake in the United States.

Especially perniciously, SSBs have essentially no effect on satiety, …