We previously showed a difference in changes of Raacetate between lean youth and youth with obesity after lactulose ingestion.12 Herein, we further expand on this, finding that within the group of youth with obesity, those with a higher degree of insulin resistance show a smaller increase in the rate of appearance of acetate after lactulose, despite similar hydrogen production among the groups. This evidence concerns the gene INS and obesity due to melanocortin 4 receptor deficiency.