A predominantly plant-based diet would aid low- and middle- income countries to deviate from the existing negative trends in health and environmental outcomes. Taking Mexico as case study, we assessed the impact of adopting such a diet on multiple food system indicators and identified a menu of fiscal policies to reach the intake targets determined in the EAT-Lancet framework. A macroeconomic model named MAGNET and a Quadratic Almost Ideal Demand System model were employed for the analysis. Two diets were modelled, an adaptation of the EAT diet considering existing intakes in Mexico and a version proposed here based on traditional eating patterns (i.e., Milpa diet). Our results showcased that the magnitude of the changes needed to attain the proposed dietary intakes is such that fiscal policies alone were found implausible. We thus modelled the change to two thirds of the EAT targets by 2040 (the goal was 100% of the EAT targets by 2050). Still, to keep fiscal policies feasible (up to +/-80% ad-valorem tax rates) 75% of the required change in consumption would need to come from other strategies. Substantial environmental gains are expected from the adoption of the EAT diet, and at the same time, foods would be more affordable for all but the poorer households. At the household level, subsidies would improve the intakes of fruits, vegetables and added fats, but the targets would be attained only by the highest income households and possibly by the urban households. Subsidies would be ineffective to reach the intake target for plant-based proteins. Given the projected progress, increased taxes are strongly advised for the foods with targeted intake reductions, particularly for the well-off and urban households. Policy makers should be cautious in the design of taxes to dairy foods, as these could lead to excessive intake reductions among vulnerable populations.