Sixty patients with a BMI of 40–47 kg/m² scheduled for primary total hip or knee arthroplasty were randomized to receive either a 12-week preoperative weight loss intervention involving video calls with dietitians and a mobile app (n=31) or standard care (n=29). The primary outcome was 12-week change in weight. Secondary outcomes included BMI reduction, proportion achieving ≥9 kg weight loss, achieving BMI <40 kg/m², changes in KOOS, HOOS, and LEAS scores, and surgical complications. Outcomes were assessed at 6 and 12 weeks, with follow-up for complications up to 1.8 years. Overall, the results revealed a modest, nonsignificant trend toward greater weight loss in the intervention group. The intervention was feasible, acceptable, and well-received. However, the modest weight loss suggests that more intensive strategies may be needed for meaningful clinical improvements before TJA.