Background: The study aimed to investigate the association between fat body mass and bone mineral density (BMD) of the lumbar spine (L1-L4), femoral neck, and total body.

Methods: We studied 95 patients with Crohn's disease (CD), 68 with ulcerative colitis (UC), and 40 healthy adults (control group-CG) aged 18-50 years old. The BMD of lumbar spine and femoral neck was assessed as well as body composition.

Results: A lower fat mass percentage was observed in about 8% of CD, 13% of UC, and 3% of CG. An increased percentage of fat mass was common, and occurred above 50% of CD, 40% of UC, and about 60% of CG. Body fat mass and fat mass percentage were significantly lower among UC compared with the CG (p-value < 0.001) and CD (p-value < 0.01) in women. Body fat mass correlated positively with the BMD and T-score of L1-L4 and total body mass in men with UC. We found a positive correlation between the fat body mass and BMD and T-score of L1-L4, femoral neck, and total body in women with IBD. Among CG, positive correlations occurred between the fat body mass and BMD of L1-L4, BMD of total body, and T-score of total body, but only in men. CRP (C-reactive protein) correlated negatively with fat body mass only in men with CD.

Conclusions: A higher fat mass percentage is common among IBD patients and healthy adults despite a normal body mass index. Body fat mass is a predictor of nutritional status and likely influences the course of the disease, as it correlated positively with BMD, T-score, and Z-score. The association between fat tissue and bone health appears to be stronger in women. Further studies are needed to investigate additional factors that may affect bone health in IBD.