Endoscopic bariatric therapies (EBTs) are promising strategies for the treatment of obesity. However, there is still great variability in its effectiveness in weight loss. Thus, we investigated whether adherence to healthy lifestyle habits is a significant determinant of weight loss effectiveness among patients undergoing EBTs. Additionally, the role of eating behaviors and psychological traits in the effectiveness of weight loss was studied. A cohort of 361 participants (81.4% women; age 41.8 ± 9.5 years; BMI 37.8 ± 4.3 kg/m2) was followed for 1 year after EBT. Anthropometric parameters, adherence to healthy lifestyle habits, emotional eating, and psychological traits (anxiety and depression) were evaluated. General linear models were used to compare outcome variables according to weight loss effectiveness groups (poor vs. good weight-loss-responders). Additionally, a hierarchical linear regression model was used to determine whether adherence to healthy lifestyle habits, emotional eating, or psychological traits were significant predictors of excess weight loss (%EWL). One year after EBT, weight loss differed significantly between good and poor weight-loss-responders (67.5% EWL [95% CI: 64.2, 70.8] vs. 28.2% EWL [95% CI: 25.5, 30.9], p < 0.001). Participants who adhered to good lifestyle habits had 4.37 more odds [95% CI: 2.19, 8.88] of being good weight-loss-responders. We also observed that eating four to five meals/day and practicing muscle-strengthening activities >2 times/week were the two lifestyle habits that most significantly determined weight loss response. Furthermore, our results revealed that while adherence to healthy lifestyle habits was a significant determinant of %EWL 3, 6, and 12 months after EBT (p < 0.001), emotional eating was a significant determinant of %EWL only 3 and 6 months after the intervention (p < 0.01 and p < 0.05, respectively). Regarding psychological traits, we observed that neither anxiety nor depression were significant determinants of %EWL. Our results revealed that adherence to healthy lifestyle habits is a significant determinant for weight loss effectiveness among patients with obesity undergoing EBT. These findings highlight the importance of implementing an adequate nutritional intervention program, especially since patients who adhere to good lifestyle habits are able to achieve a weight loss that would be comparable with bariatric surgery.