Quantitative trait locus analysis of dietary obesity in C57BL/6 and129P3/J F2 mice revealed that the AhR gene is one of seven candidate genes associated with increased body weight.29 Moreover, a shift in the ratio between Bacteroidetes and Firmicutes in the intestine has been linked with development of obesity in both mice and humans.30–34 We did not observe a difference in weight gain between AhR−/− and AhR+/+ mice on HFD. This evidence concerns the gene AHR and obesity due to melanocortin 4 receptor deficiency.