Obesity and Its Related Diseases in China: The Impact of the Nut ...

In addition to total fat intake, composition of different types of dietary fats might affect insulin sensitivity and lipid metabolism. Animal studies showed that a diet rich in saturated fat impaired insulin action; whereas a diet rich in unsaturated fat, especially ω₃fatty acids, improved insulin action (59). However, human studies have thus far been negative (60–63). As for lipid metabolism, low SFA, high MUFA, or PUFA consumption combined with medium total fat intake may be beneficial to lipid profile and cardiovascular health (64, 65). Conversely, extremely low fat intake was associated with high triglyceride, high VLDL-cholesterol, and decreased LDL- and HDL-cholesterol concentrations (66–68).

In most of these studies, the type of dietary carbohydrate has not been taken into account, so it is unknown whether it will less adversely affect lipid metabolism and/or improve insulin sensitivity more if a high-carbohydrate low-fat diet enriched with complex carbohydrate and fiber is taken (49). Further studies are needed to illustrate how the composition of dietary carbohydrate (simple, complex carbohydrate and fiber) and fat (SFA, MUFA, and PUFA) affects adiposity and metabolic disorders.

Physical Activity. Sedentary lifestyle has been reported to in-crease the risk of obesity and insulin resistance. Nonvigorous as well as vigorous exercise was associated with significantly im-proved insulin sensitivity (69). Physical activity directly improves insulin sensitivity by increasing the number of glucose transporters in both muscle and adipose tissue immediately, which secondarily improves insulin-mediated glucose disposal (70, 71). Also physical activity increases oxidation of fatty acids, therefore it can increase insulin sensitivity by reducing lipid overload (49).

Numerous studies have shown that increased physical activity at least can stabilize body weight and may lead to modest weight reductions (72).