Iron Deficiency Is Associated with Increased Circulating Fatty Acids and Unfavorable Body Composition in Women with Obesity

Iron deficiency (ID) is a nutritional disorder prevalent in obesity. Because iron is crucial for mitochondrial function, lipid oxidation, and systemic inflammation, processes altered in obesity, we investigated how ID affects body composition, plasma metabolites, and bariatric outcomes in 14 women (ID: n = 7; iron sufficient (IS): n = 7; aged 36 ± 8.3; BMI > 30 kg/m2). Before surgery, the ID group showed higher fat mass (IS: 48.3 ± 6.0 kg; ID: 59.4 ± 8.5 kg; p = 0.038) and elevated circulating fatty acids. Body fat mass correlated negatively with ferritin (rho = −0.62, p = 0.02). ID also showed a lower muscle-to-fat ratio (IS: 0.69 ± 0.18; ID: 0.51 ± 0.08; p = 0.053). One year after surgery, the ID group had a lower skeletal muscle mass percentage (IS: 41.2 ± 1.9%; ID: 34.1 ± 2.9%; p = 0.011) and reduced muscle-to-fat ratio (IS: 1.58 ± 0.27; ID: 1.00 ± 0.19; p = 0.038). Valine and leucine decreased only in the ID group. The iron deficiency worsens obesity-related outcomes.