Purpose The COVID-19 pandemic could exacerbate the risk factors for weight gain in patients with previous bariatric surgery. The aim of this study was to evaluate factors related to weight gain during lockdown in patients with a sleeve gastrectomy. Materials and Methods A group of 48 obese subjects with previous bariatric surgery was enrolled. After a 7-week confinement, a telephone interview was conducted. In this phone call, self-reported body weight gain and different factors were recorded. In order to obtain the basal and pre-surgical data, biochemical and anthropometric parameters were recorded from electronic medical record. Results The mean age was 45.3±8.0 years (range: 23–61) and the mean body mass index (BMI) was 32.5±7.5 kg/m2 (range: 28.6–34.2). Gender distribution was 38 females (79.2%) and 10 males (20.8%). The increase in self-reported body weight was 3.8±2.1 kg during the 7 weeks of confinement. And the self-reported body weight gain was lower in subjects with regular exercise (4.6±0.9 vs 1.1±0.3 kg; p =0.02). The number of face-to-face visits to the nutrition office that did not attend was 0.61±0.81 (range: 0–4) per patient. In the multiple regression analysis with self-reported body weight gain as a dependent variable, the physical activity (minutes/week) remained as a protective factor with a beta coefficient of −0.09 (95% CI: −0.001 to 0.016; p =0.03) and number of face-to-face appointments in the nutrition consultation missed as a risk factor with a beta coefficient of 9.65 (95% CI: 1.17–18.12; p =0.03). Conclusions The increase in self-reported body weight is associated with a decrease in physical activity and the loss of face-to-face visits to the Nutrition Unit.