2014 年 3 巻 5 号 p. 501-505
Insulin resistance induced by obesity is important in the pathogenesis of metabolic syndrome and type 2 diabetes. On the other hand, recent data suggest that ectopic fat accumulation in muscle and liver induces insulin resistance in these organs, independent of obesity. For example, short-term calorie restriction greatly decreased intrahepatic lipid levels and improved hepatic glucose metabolism in patients with metabolic disease. In addition, short-term aerobic exercise decreased intramyocellular lipid accumulation and improved insulin resistance in skeletal muscle. Similarly, physical inactivity was identified as a risk factor of intramyocellular lipid accumulation during a 3-day high fat diet. Considering the fact that metabolic diseases are frequently observed in lean subjects in East Asian countries, ectopic fat accumulation in insulin target organs may be an important pathogenesis of, as well as a therapeutic target of, metabolic diseases in non-obese subjects. Thus, it may be more appropriate to call fat accumulation in insulin target organs as “intracellular obesity” rather than ectopic fat. Furthermore, it is important to perform additional research to clarify the pathogenesis of metabolic diseases in non-obese subjects.