Effects of social influence and body type on the food choices of others and its associated environmental impacts in Vietnam

Abstract This study investigates how peer body attributes (thin vs. obese) and normative portion anchors influence food selection, actual consumption, and downstream organic waste among consumers in Vietnam. Integrating behavioral decision theory with Life-Cycle Assessment (LCA) principles, three controlled lab experiments were conducted with university undergraduates (N = 692 total across studies) to evaluate portion adjustments under varying conditions of food healthiness, cognitive load, and appearance self-esteem. Results indicate that consumers utilize observed peer portion choices as primary quantity anchors, but systematically adjust decisions based on peer physical attributes: participants selected significantly larger portions near thin peers selecting unhealthy options, yet adjusted portions downward near obese peers. This downward adjustment was attenuated under high cognitive load and moderated by appearance self-esteem. Behaviorally, social modeling caused a severe decoupling between serving size and actual intake, leaving up to 61% of selected food unconsumed. By translating discarded food volume into lifecycle carbon footprints (Ef = 1.60-5.40 g CO2e per unit/gram), we demonstrate that large peer anchors act as environmental multipliers, increasing waste-driven greenhouse gas emissions up to 27.5-fold (93.69 g vs. 3.40 g CO2e per serving). These findings highlight how social portion anchoring directly drives localized organic waste and supply chain carbon burdens, underscoring the need for default portion architecture and targeted menu sizing in the food and beverage industry.