Background: Workplace wellness programs have been widely implemented to promote employee health outcomes and reduce health costs. However, little is known about how designs of wellness programs matter for best promoting positive employee health outcomes. Purpose: This research aims to identify the most effective designs of workplace wellness programs resulting in positive employee health outcomes. Methods: We conducted endogenous treatment analyses to compare the effectiveness of three wellness programs (diabetes prevention, hypertension prevention, and nutrition classes) on employees' health outcomes. Data were analyzed from 24,117 full-time employees who received the pre- and post-intervention biometric screening in 2012-2016 at a large employer in Texas, U.S. Results: Unlike the mixed effects in diabetes and hypertension prevention programs, the nutrition program, which exhibited a high level of topic relevance, impact, and intensity, significantly decreases all four biometric indicators: decreasing systolic blood pressure (4%), diastolic blood pressure (10%), glucose (2%), and cholesterol (26%), which improves health outcomes. Discussion: This study prompts health educators to consider comparative effectiveness of workplace wellness programs for maximized impact on employees' health outcomes. Translation to Health Education Practice: Designing wellness programs with high topic relevance, impact, and intensity should be emphasized in implementing workplace wellness programs.