This essay critically appraises three epidemiological studies examining the relationship between obesity and depression in adolescents and young adults. The studies include a cross-sectional study, a case-control study, and a longitudinal/cohort study. The essay uses the CASP (Critical Appraisal Skills Programme) checklist to evaluate each study's methodology, including participant selection, exposure and outcome measurement, confounding factors, and statistical analysis. The essay highlights the strengths and weaknesses of each study, assessing their validity, reliability, and potential biases. It also examines the study findings, including the association between obesity and depression, and their implications for public health practice. The author synthesizes the evidence to determine the credibility and applicability of the results, considering the limitations of each study design. The essay concludes with a discussion of the implications of these findings for understanding and addressing the co-occurrence of obesity and depression, and the need for further research to clarify the relationship between these two conditions.