Online Mental Contrasting with Implementation Intentions for changing snacking behavior and reducing body mass index in people with excess weight: a randomized controlled trial González Pérez, Raquel Solier López, Lucía Vilar López, Raquel Verdejo García, Antonio Navarro Pérez, Carmen Flores Caracuel Romero, Alfonso Mental Contrasting with implementation intentions Implementation intentions Excess weight Obesity Overweight Snacking BMI This work was supported by TRAINEP project [grant RTI2018–098771-B-I00] funded by Spanish Ministry of Science, Innovation, and Universities [MCIN/AEI/10.13039/501100011033] and the European Regional Development Fund “FEDER A way of making Europe”; INHIBE project [grant PDI2022-137524OB-I00] funded by Spanish Ministry of Science, Innovation, and Universities [MCIN/AEI/10.13039/501100011033] and the European Social Fund Plus (FSE+); BE-NEMOIC project [grant P21_00776] funded by Consejería de Universidad, Investigación e Innovación (Junta de Andalucía); Centro de Investigación Mente, Cerebro y Comportamiento grant [Grant CEX2023-001312M] funded by Spanish Ministry of Science, Innovation, and Universities [MCIN/AEI/10.13039/501100011033]; Formación de Profesorado Universitario [Contract FPU2020-04540 (RGG)] funded by Spanish Ministry of Science, Innovation and Universities; Research stays in foreign centres funded by Spanish Ministry of Science, Innovation and Universities [grant EST25/00046 (RGG) and PRX22/00698 (AC)] and University of Granada [Plan Propio de Investigación y Transferencia 2024-Programa 10 (RGG and LSL)]. This study was made possible with the financial support of the organizations mentioned in Funding section. Funding for open access charge: Universidad de Granada/CBUA. Mental Contrasting with Implementation Intentions (MCII) has proved useful for dietary changes, but not yet applied to people with excess weight. We aimed to determine the benefit of online MCII as an add-on to a standard Behavioral Weight Loss Intervention (Treatment as Usual-TAU) to change snacking behavior -one of the main contributors to excess weight- and reduce BMI. This online randomized controlled trial included 148 participants [MCII-group (50), Sham-group (50) and TAU-group (48)]. All participants received standard intervention: motivational interviewing, individualized diet and physical exercise. MCII and Sham groups received training for one week, while TAU-group had monitoring. Outcome measures were self-reported snacking behavior (frequency of snacking, total servings, ultra-processed food -UPF- servings) and BMI. Results of mixed ANOVAS showed interactions group x time (pre-vs post-treatment) for all variables: frequency of snacking [F (2,134) =6.110, p =.003], total servings [F (2,126) =4.291, p =.016], UPF servings [F (2,127) = 4.059, p =.020], and BMI [F (2,98) =3.990, p =.022]. The MCII-group showed differences with Sham and TAU groups at post-treatment in all snacking behavior variables, with large effect sizes between the MCII-group and the other two groups, and null between Sham and TAU groups (except for UPF servings). Complimentary one-way ANOVA for standardized change showed greater BMI reductions for the MCII-group [F (2,103) =3.990, p =.006], with moderate effect sizes. In conclusion, MCII improves the results of usual treatment for excess weight in snacking behavior and BMI. Trial registration: Clinical Trials NCT05158075. 2025-09-17T06:24:46Z 2025-09-17T06:24:46Z 2025-06-26 journal article González-González, R., Solier-López, L., Vilar-López, R., Verdejo-García, A., Navarro-Pérez, C. F., & Caracuel, A. (2025). Online Mental Contrasting with Implementation Intentions for changing snacking behavior and reducing body mass index in people with excess weight: a randomized controlled trial. Appetite, 214, 108209. https://doi.org/10.1016/j.appet.2025.108209 https://hdl.handle.net/10481/106357 10.1016/j.appet.2025.108209 eng http://creativecommons.org/licenses/by-nc-nd/4.0/ open access Attribution-NonCommercial-NoDerivatives 4.0 Internacional Elsevier