Fish oil suppresses obesity more potently in lean mice than in diet-induced obese mice but ameliorates steatosis in such obese mice

This study sought to clarify the antiobesity effects of fish oil (FO) in terms of prevention and amelioration. An isocaloric diet composed of lard or FO was given to lean C57BL/6J mice for the study of prevention and high-fat diet-induced obese (DIO) mice for the study of amelioration for 4 weeks. Body weight gain and food efficiency were potently suppressed by FO in lean mice compared to lard diet-fed mice. Uncoupling protein-1 (UCP-1) expression in inguinal white adipose tissue (WAT) was also significantly induced by FO in lean mice. FO also suppressed body weight gain and food efficiency in DIO mice but did not reduce body weight. FO ameliorated liver steatosis in DIO mice by mildly inducing UCP-1 in inguinal WAT. FO suppressed obesity more potently in lean mice than in DIO mice but ameliorated steatosis in the DIO mice.