Unhealthy lifestyle behaviors, namely poor diet and inadequate physical activity, significantly contribute to poor health and obesity risk, which in turn impact chronic illness outcomes. A possible approach to improving these health behaviors and subsequent outcomes is to capitalize on the theorized link between social movement involvement and overlapping health behaviors. Social movement involvement may be a viable stealth intervention for health, utilizing intrinsic motivators to improve health without an explicit focus on changing health behavior. Thus, the current study explored the links between social movement involvement and diet and physical activity. Two samples from a college population (N = 196) and the general population (N = 195) participated in an online survey, which included measures of social movement involvement, social movement-related health behaviors and dietary intake and physical activity. After controlling for known covariates, social movement-related health behaviors mediated the relationship between level of social movement involvement and fruit and vegetable consumption, whole grain intake and average daily physical activity in both samples. These findings suggest that health behaviors associated with social movement involvement may be an important mechanism in promoting health among social movement members and that the model holds across adult populations. This research adds to existing literature on stealth interventions as a viable means of improving important behavioral health components linked with obesity and chronic disease and supports social movement involvement as a potential form of stealth intervention.