Obesity is one of the greatest public health challenges of modern times and its prevalence is increasing worldwide. With food so abundant in developed countries, many people face a conflict between desires for short-term taste and the goal of long-term health, multiple times a day. Recent research suggests that consumers often resolve these conflicts based on their lay beliefs about the healthiness and tastiness of food. Consequently, such lay beliefs can play critical roles not just in food choice but also weight gain. In this research, we show, across six countries and through mediation analysis, that adults who believe that tasty food is unhealthy (the Unhealthy = Tasty Intuition, or “UTI”; Raghunathan, Naylor, & Hoyer 2006) are less likely to consume healthy food, and thereby have a higher body mass index (BMI). In Study 1, we conducted a cross-sectional survey in five countries (Australia, Germany, Hong Kong, India, and the UK), and found that greater strength of belief in UTI was associated with higher BMI, and this relationship was mediated by lower consumption of fruits and vegetables. The observed patterns largely converged across the sampled Western and Asian-Pacific countries. In Study 2, we teased apart the mediating role of vegetable versus fruit consumption and also addressed the issue of reversed causality by predicting BMI with a measure of UTI belief taken 30 months previously. We found that vegetable consumption, but not fruit consumption, mediated the association between UTI belief and BMI. Our findings contribute to the literature by showing how lay beliefs about food can have pervasive and long-lasting effects on dietary practices and health worldwide. Implications for public policy and health practitioners are discussed.