Fish oil induces thermogenesis in diet-induced obese mice in brown adipose tissue, but not in white adipose tissue.

The ω3 polyunsaturated fatty acids in fish oil enhance heat production in adipocytes and exert anti-obesity effects, but the effects of fish oil on heat production in diet-induced obese (DIO) mice are unclear. We examined whether diets containing fish oil increased the expression of heat-producing genes in adipose tissue and increased body temperature in DIO mice, resulting in weight loss. C57BL6/J mice were fed a lard-based high-fat diet for 8 weeks starting at 5 weeks of age and then divided into two groups: one group was fed a fish oil-based high-fat diet, and the other group was fed a lard-based high-fat diet continuously for another 8 weeks. Mice fed a fish oil-based high-fat diet lost body weight gain, adipose tissue weight gain, and reduced insulin/leptin resistance. In addition, the rectal temperatures of mice fed a fish oil-based high-fat diet remained higher. In DIO mice fed a fish oil-based high-fat diet, the FGF21 expression in BAT increased. In conclusion, the administration of fish oil increased the expression of heat-producing genes in brown adipose tissue (BAT) but did not alter heat-producing genes in inguinal white adipose tissue (WAT).