Taxes and subsidies imposed on foods, beverages or their component nutrients are proposed to improve health through a simple causal pathway [1]-[5]. First, they might induce changes in the relative prices of less healthy foods and drinks compared with healthier alternatives. Second, these price changes might incentivise enough people to purchase and consume an overall healthier diet, leading to meaningful reductions in the prevalence of risk factors for non-communicable diseases. Despite considerable uncertainty surrounding both of these propositions, this logic forms the basis of the argument for calls to governments to introduce food taxes and subsidies ? especially taxes on sugar-sweetened beverages ? as part of broader public health strategies to improve people?s diets [1]-[5].