The impact of obesity on clinical outcomes following joint replacement procedures is resounding. Therefore, multiple strategies to achieve a substantial weight loss before surgery are needed in obese patients. The aim of the study was to test the effect of a fiber-enriched high carbohydrate (FEHC) diet on the reduction in body weight and pain in elderly obese patients undergoing total hip arthroplasty (THA). Sixty-one candidates for THA were included in our study. Prior to the procedure, the participants have been randomly assigned to a 3-month diet intervention (FEHC diet or free diet). Anthropometric measures and food questionnaires were collected at the enrollment and after 3 months. The Oxford Hip Score (OHS), the Hip disability and Osteoarthritis Outcome Score (HOOS) and the Western Ontario McMaster Universities OA Index (WOMAC) were administered at baseline and before surgery. A statistically significant variation of weight was found in the FEHC diet group (-3.7 kg, -4.4--2.5) compared to the control group (-0.2 kg; -1.4-1.7; p < 0.0001), as well as significant improvements in the OHS (p < 0.0001), the HOOS (p < 0.0001) and the WOMAC (p < 0.0001) questionnaires. According to the results of the study, the FEHC diet in obese patients undergoing THA might help weight loss and improve related anthropometric parameters as well as hip function and pain.