Up to one-quarter of individuals currently labeled as obese are actually metabolically healthy. Though obesity is a major risk factor for diabetes, the two conditions aren’t always linked. A new study sheds light on a possible explanation, revealing that high levels of a molecule HO-1 are linked to poor metabolic health and an increased risk of type 2 diabetes in obese humans. HO-1 blockers could represent a promising new strategy for the treatment of metabolic disease.