How to set up an effective food tax?

Whereas public information campaigns have failed to reverse the rising trend in obesity, economists support food taxes as they suggest they can force individuals to change their eating behavior and make the agro-food industry think more about healthy food products. Excise taxes based on the unhealthy nutrient content would be more effective since they impact more on unhealthy food products than VAT (value-added-tax) taxes. Taxes based only on junk food products would avoid perverse effects on healthy nutrient. However, as eating behavior of consumers is complex, a modeling analysis would allow to assess unexpected effects on other unhealthy nutrients or products