Metabolic syndrome (MetS), a global public health problem, is the primary cause of type 2 diabetes and cardiovascular disorders. Lifestyle modification interventions (dietary and physical activity modifications) are effective in preventing and ameliorating MetS and associated comorbidities. However, the impact of lifestyle changes on MetS among Mexican Americans has yet to be investigated, particularly due to high attrition rates in this population. The overall goal of the explanatory mixed-methods study presented in this dissertation was to identify efficacious lifestyle modification efforts directed towards Mexican Americans to promote their retention in lifestyle modification programs, ameliorate the severity of MetS, and understand underlying behavior modification process. In particular, we examined secondary data from an extensive study Beyond Sabor to 1) examine predictors of program completion, 2) compare variation in MetS severity scores (z-scores) between intervention (Beyond Sabor) and attention control (Healthy Living) groups, over time and, 3) investigate processual development of self-efficacy in a sample of 1153 disadvantaged Mexican Americans participants. Findings suggest that program completers were more likely to be older, had more years of education, lower fasting blood glucose levels, and participated in sites with high group cohesiveness. Results also revealed that when compared with the standard nutrition program, Healthy Living, the lifestyle modification intervention, Beyond Sabor, was more effective in ameliorating MetS severity, systolic blood pressure, triglyceride, and fasting plasma glucose levels among study participants. Qualitative results demonstrate the high acceptability of Beyond Sabor intervention. Four sub-themes emerged illustrating important underlying conditions contributing to participants’ improved self-efficacy: desire to gain knowledge about ways to improve health, development of social support, adoption of program teachings in family lifestyle, and improvement in health outcomes. Findings of the current study may allow researchers to identify Mexican Americans at risk of non-completion and to develop strategies to improve lifestyle modification program attendance, and thus health outcomes. Qualitative findings underscore the importance of sociocultural context on individuals’ attempts to make lifestyle changes to manage their chronic illnesses. Successful adaptation of lifestyle interventions such as Beyond Sabor for at-risk populations in community-based settings will be critical in stemming the tide of MetS.