Due to the retention of 78.1% of the participants obtained for the first measurement (after the December holidays), we believe that waiting one more year to complete the study would not be feasible for a subsequent definitive study.

Introduction. Obesity is the main risk factor for the development of chronic degenerative diseases in Mexico and other countries around the world. Due to the difficulty of treating obesity, it is necessary to change the curative paradigm for a preventive one. A review showed that holiday periods during the year are critical points for weight gain. The holiday season is the festive period with the greatest impact on adults' body weight. Observational studies have shown that more than 50% of the annual weight is gained during this period. However, few preventive interventions in the festive period have been carried out globally. Additionally, the COVID-19 pandemic seems to be negatively affecting diet, physical activity and body weight. So preventive interventions are needed, especially those that can be implemented in an online format. The purpose of the study is to evaluate the effect of two online interventions -Watch your Weight during the Holidays Program and the Relative 5:2 Fasting - on the prevention of body weight gain from baseline to 8 weeks in comparison with a control group in Mexican adults during the COVID-19 pandemic. Methodology: This is a Pilot Randomized Controlled Trial (RCT). The primary outcome is the change in body weight from baseline to 8 weeks. Secondary outcomes are the percentage of retention / desertion of the participants, adherence to interventions, participant satisfaction scale, changes in other obesity parameters, biochemical, physical, and quality of life variables from baseline to 8 weeks. Obesity and quality of life parameters from baseline to 52 weeks are also secondary outcomes. The statistical analysis of the primary and secondary variables will be conducted, according to their distribution, by intention to treat and, secondarily, by completer´s analysis.

Inclusion Criteria:

• Mexican adult participants (≥20 and ≤60 years)
• Residents of the city of Hermosillo, Sonora
• Body Mass Index ≥ 23 kg/m2 and ≤ 40 kg/m2
• Availability and motivation to attend the intervention program
• Committed to not undertake any other intervention in place of, or in combination with, the one assigned in the study during the 8 weeks of the intervention

Exclusion Criteria:

• Diagnosed medical conditions that constitute a contraindication for intervention such as: diabetes, hypertension, diseases with an effect on body weight (for example: liver failure; cancer in treatment or in advanced stage; history of COVID-19 that required hospitalization, supplemental oxygen or has left sequelae that contraindicates the intervention; psychiatric conditions; eating disorders, etc.).
• Use of drugs or substances with an effect on weight, for example, metformin, orlistat, corticosteroids, etc.
• Use of addictive substances such as drugs of abuse
• Previous bariatric surgery.
• Being a participant in another intervention or treatment for the management of obesity.
• Weight loss > 5% of total body weight in the last 4 months.
• Having plans to become pregnant within the study period, currently pregnant or breastfeeding.
• Another family member has agreed to participate in the study.
• Illiteracy.