Objectives: To evaluate the effect of the SARS-CoV-2 lockdown on dietary habits, body weight, left hepatic lobe volume, use of micronutrient supplements, micronutrient status, frequency of physical activity, and evolution of comorbidities in patients undergoing preoperative care for BS. Materials and Methods: We prospectively evaluated the dietary habits (including use of micronutrient supplements and frequency of physical activity) of 36 patients who were candidates for BS from March to May 2020; 7-day food dietary records, body weight, left hepatic lobe volume by ultrasound, micronutrient status, and evolution of comorbidities were assessed. Results: All patients completed the study. Of the participants, 44.4% (16/36), 47.2% (17/36), and 27.8% (10/36) followed the preoperative indications for vegetables, fruits, and legumes, respectively, whereas over 50% did not. Furthermore, 30.6% (11/36) and 55.6% (20/36) of participants followed the prescribed recommendations for carbohydrates/sweets products and alcohol, respectively. A total of 61.1% (22/36) of participants experienced new foods and new culinary preparations. In addition, at the time of the study, we found that only 11.1% (4/36) were engaged in prescribed physical activity and only 36.1% (13/36) were taking prescribed micronutrient supplements. Compared to the initial weight, we observed an increased body weight and body mass index (+4.9%, p = 0.115; +1.89%, p = 0.0692, respectively), and no improvement in left hepatic lobe volume, micronutrient status, or comorbidities was recorded for any patient in the anamnesis. Conclusions: Lockdown determined by the SARS-CoV-2 pandemic has negatively affected the preoperative program of BS candidates, resulting in a postponement to the resumption of bariatric surgical activity.