Traditional-to-modern food value chain transformations are widely occurring in the Global South. The transition to food retailing often involves higher use of resources to comply with quantity and quality requirements, which might modify the environmental profile of products. This study aims to quantify carbon footprints and food losses and waste along different trajectories of vegetable value chains in Thailand. We used a methodological framework based on Life Cycle Analysis (LCA) of two horticultural products, onion (Allium cepa L.) and Chinese cabbage (Brassica rapa, subsp. Chinensis). Following a systemic approach, we gathered primary data using resource flow diagrams, mass balances and surveys at each node of traditional and modern value chains, from the farm, to traders-distributors and finally wholesale markets and retailers. Cradle-to-farm gate stage remained as the main greenhouse gas hotspot along the value chain –primarily due to fertilizer production and application– and no differences were encountered between production for modern and traditional markets. Although the largest share of the product carbon footprint was found at the farm gate, food wastage at later stages on the value chain were generally larger in volume. Among the food waste management options, the disposal in agricultural fields and the use as animal feed had the highest potential to reduce carbon footprints.