We analyze how a sales tax levied on all food products impacts the consumption of healthy food, unhealthy food, and obesity. The sales tax can stimulate the consumption of healthy meals by lowering the time costs of food preparation. Moreover, the sales tax lowers obesity under more general conditions than a tax on unhealthy food (fat tax) and a subsidy on healthy food (thin subsidy). We calibrate the model using recent consumption and time use data from the US. The thin subsidy is counterproductive and increases weight. While both the sales tax and the fat tax mitigate obesity, the former imposes a lower excess burden on consumers.
It seems that if you try to tax fat directly, individuals can readily substitutes into other foodstuffs that are bad for them, or bad for their weight. If you place a sales tax on food in general, individuals substitute into eating more at home, and there the food is healthier in the first place and furthermore the time-intensiveness of production will limit the number of dishes prepared and thus quantity and in turn obesity.