On the basis of the spillover or transfer effect and the transtheoretical model of change, this study assessed the association between amount of physical activity, healthy and unhealthy weight control behaviors, and motivational types, as well as their variability across stages of change. A total of 1219 randomly selected Mexican adults from 18 to 65 years old, representative of the city of Monterrey (México), participated in the study. Correlation analyses, differences by gender, and multivariate analyses of variance, controlling for age, were performed. We found that in the maintenance stage, there is higher frequency of physical activity more healthy weight control behaviors, as well as higher autonomous motivation. In the contemplation stage, there is less physical activity, a higher frequency of unhealthy weight control behaviors, higher controlled motivation, and amotivation. Relationships were found between the healthy behaviors studied and the interaction dynamics observed across the stages of change, highlighting the key role of the contemplation and maintenance stages in weight control change. Physical activity as a targeted intervention objective could be a gateway to healthier weight control behavior, as well as higher autonomous motivation