Overweight/Obesity and Body Fat Percentage in Relation to Iron Status Among Indonesian Women of Reproductive Age: Evidence from a Case–Control Study

Background/Objectives: Obesity-related inflammation may disrupt iron homeostasis and increase the risk of iron deficiency, yet evidence among women in low- and middle-income countries remains limited. This study examined the independent association between overweight/obesity and iron status among Indonesian women of reproductive age. Methods: A case–control study was conducted among 340 nonpregnant women aged 20–29 years in Surabaya, Indonesia. Sociodemographic, dietary, menstrual, and anthropometric data were collected alongside venous blood samples. Logistic regression models were used to examine associations between adiposity measures and iron deficiency (ID), anaemia, and iron deficiency anaemia (IDA), adjusting for potential confounders. Results: Inflammation-adjusted serum ferritin was significantly higher among women with overweight/obesity than among normal-weight women (22.39 ± 21.7 vs. 17.78 ± 17.6 µg/L; p = 0.033). Consistent with this, the prevalence of ID was lower among women with overweight/obesity, likely reflecting inflammation-related ferritin elevation that may influence diagnostic classification. BMI-defined overweight/obesity was not independently associated with ID, anaemia, or IDA. In contrast, higher body fat percentage was inversely associated with ID (AOR 0.93; 95% CI 0.86, 0.99) and IDA (AOR 0.86; 95% CI 0.75, 0.99). Elevated alpha-1-acid glycoprotein (AGP) was independently associated with higher odds of IDA, and menstrual iron loss was an independent predictor of anaemia and IDA. Conclusions: BMI alone is insufficient to capture the relationship between adiposity and iron status in women of reproductive age. Body fat percentage appears to be a more sensitive indicator of adiposity-related iron risk. These findings suggest that inflammation associated with adiposity may alter iron biomarkers, and reliance on BMI alone may obscure the true burden of iron deficiency in this population.