OBJECTIVE Obesity and low-back pain associated with degenerative spondylosis or spondylolisthesis are common comorbid conditions. Many patients report that the pain and disability associated with degenerative lumbar disease are key factors in their inability to lose weight. The aim of this retrospective study was to determine if there is an association between improved functional status and weight loss following a successful transforaminal lumbar interbody fusion (TLIF) procedure. METHODS A retrospective cohort study of patients who underwent single-level TLIF was performed. Inclusion criteria were preoperative body mass index (BMI) greater than 30 kg/m², achievement of minimum clinically important difference in the Oswestry Disability Index (ODI, defined as improvement of 15 points), and minimum 1-year postoperative followup BMI. Preoperative and postoperative BMI, ODI, and visual analog scale (VAS) scores were compared. A subgroup analysis of patients who achieved substantial clinical benefit (SCB, defined as a net improvement of 18.8 points on the ODI) was also performed. RESULTS A total of 56 patients met the inclusion criteria. The mean age of the study population was 55.6 ± 13.7 years. The mean preoperative BMI was 34.8 ± 4.6 kg/m², the mean preoperative ODI was 66.2 ± 10.1, and the mean preoperative VAS score was 7.1 ± 1.7. The mean change in ODI was -33.1 ± 13.5 (p < 0.01) and the mean change in the VAS score was -4.1 ± 2.1 (p < 0.01). The mean change in BMI was +0.15 ± 2.1 kg/m² (range -4.2 to +6.5 kg/m²; p = 0.6). SCB was achieved in 46 patients on the ODI. The mean preoperative BMI for patients with SCB was 34.8 ± 4.8 kg/m², and the mean postoperative BMI was 34.7 ± 5.0 kg/m². The mean change in BMI was -0.03 ± 1.9 kg/m² (p = 0.9). CONCLUSIONS Despite successful surgical intervention via TLIF with achievement of improved function and pain, obese patients did not have significant change in weight postoperatively.