Consistent with prior reports showing that circulating FGF21 levels are influenced by BMI (44–46), and that individuals with obesity and metabolic syndrome have greater FGF21 responses to ingested monosaccharides (4,6), we found that BMI was associated with greater FGF21 responses to the acute ingestion of the commonly consumed sugar, sucrose. The gene discussed is FGF21; the disease is obesity due to melanocortin 4 receptor deficiency.