However, because nutritional fatty acids, whose blood levels are often increased in obesity, have been shown to activate the TLR4 signaling and induce inflammatory signaling in adipocytes in vivo7, a possibility could not be excluded that saturated fatty acids were involved in the enhanced bioluminescence in the obese adipose tissue of mice with HFD. Here, TLR4 is linked to obesity due to melanocortin 4 receptor deficiency.