Efectos heterogéneos en la demanda ante un impuesto al refresco en México[Will the poor and high consumers benefit more by obesity prevention fiscal policies? Evidence from Mexico]

The increasing burden of obesity and related non-communicable diseases in the world has encouraged the design of effective policies in order to contain this trend. Excise taxes on low-nutritious food and sugar-sweetened beverages consumption, such as soft-drinks, have been proposed. Currently, a growing number of studies have calculated potential effects of soft-drinks taxes considering data for average consumers, and have assessed effectiveness of such measure on raising fresh revenues to the government, modifying consumption patterns, and population weight reduction. Nevertheless, there is evidence of heterogeneity of the demand of soft-drinks related to poverty and the level of consumption of soft-drinks. It has also been emphasised the need of examining the possible distributional effects of an excise tax in populations with uneven income distribution. We used Mexican data to discuss effectiveness and equity implications of an excise tax on soft-drinks consumption in populations with heterogeneous demand. We estimated the changes in the quantity purchased and household monthly expenditure on soft-drinks of 8434 households that answered the 2005 Mexican Family Life Survey. Specific price elasticities of the demand for soft-drinks of households grouped by their level of consumption (low, medium and high) and poverty (extreme, moderate and income superior to moderate poverty) were used. Several excise tax rate scenarios were considered: from a conservative level (tax rate: t=20%), to a least conservative level (t=65%) that was defined by the longitudinal analysis of body mass index changes in adults between 2002 and 2005. Effectiveness was evaluated by revenue collection (as a proportion of the cost of a comprehensive obesity prevention strategy), changes of the patterns of consumption and changes in calories related to changes of body mass index. Equity was assessed by concentration curves and indexes of the distribution of tax burden and the distribution of changes of the proportion of food expenditure devoted to soft-drink purchasing. The results suggest although revenues collected with low tax rates (20%) could partially finance a comprehensive obesity prevention strategy for Mexico, effectiveness on changing the patterns of consumption is only observable at tax rates higher than 45%. An excise tax is not effective on modifying population body mass index if tax rates are lower than 65%. Despite the fact that effects are concentrated in high consumption households, regressiveness is a latent problem due to the high tax burden imposed to households on extreme poverty. These results are different from the ones calculated in previous exercises in Mexico, considering average consumers. If governments are considering excise taxes on soft drinks to prevent obesity, heterogeneity of the demand for soft-drinks due to poverty and consumption level should be considered, especially in emergent economies with uneven income distribution. For the Mexican case, in order to design policies that adequately affect the demand for soft drinks, tax rates superior to 45% are recommended, along with redistributional mechanisms to promote equity by compensating households in extreme and moderate poverty, and effective interventions to reduce population weight.