The United States is facing an alarming and increasing obesity epidemic. Stress is associated with obesity, but specific longitudinal effects of life trauma on weight gain have not been assessed. Here we examined if life trauma and chronic stress predicted weight gain while also measuring the impact of body mass index (BMI). Life trauma and chronic stress were assessed with the Cumulative Adversity Interview (CAI). Weight and BMI were captured repeatedly over a two-year period. Results show significant increases in weight gain over time. Individuals with obesity (IOb) reported significantly higher levels of life trauma at the onset compared to overweight (IOw) and lean individuals (Il). Greater numbers of trauma events were associated with increased weight gain for both IOb and IOw but not for Il. Increased chronic stress was not consistently associated with weight gain over time. Current findings suggest the need to address trauma coping, especially in vulnerable individuals to prevent greater weight gain and curb obesity-related health outcomes.