The prospective study presented here, comparing subjects with lean NAFLD and subjects with obesity (BMI > 30) but no demonstrable fatty liver infiltration, shows that iron metabolism parameters (haemoglobin, haematocrit, MCHC, serum ferritin, soluble transferrin receptor) are positively associated with a risk of lean NAFLD. Here, TFRC is linked to obesity due to melanocortin 4 receptor deficiency.