| Chapter 2: | Background |
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In addition, blood pressure did not overlap with other factors (39–47). Only one confirmatory factor analysis showed that these components such as obesity, insulin-glucose metabolism, lipid profile, and blood pressure were related and united by a higher-order common factor (48).
The structure of the metabolic syndrome might differ across ethnicity. Most studies in U.S. populations suggested insulin resistance as a common link for the syndrome. However, factor analysis on Hong Kong Chinese showed that hyperinsulinemia was not central to the syndrome, indicating obesity as the common link for the metabolic syndrome (39).
2.1.2.2 Risk Factors for the Metabolic Syndrome
Besides age and genetics, lifestyle factors could affect metabolicsyndrome too. These include unhealthy diet, physical inactivity, habitual alcohol drinking and smoking, and psychosocial stress.
Diet. Dietary studies have consistently showed that saturated fatty acids and trans-fatty acids could increase serum low density lipoprotein (LDL)-cholesterol concentration. Recommendations on reducing the intake of these two fatty acids have been made (49). However, the relative metabolic effects of higher intakes of carbohydrate compared with higher intakes of fat are still under debate.
Clinical trials showed that ad libitum low-fat diet might lower body weight compared with high-fat diet but only for a short term (50–53). Furthermore, when energy consumption was equal, there was no difference in the effect of low- or high-fat diet on body weight (54, 55). The association between fat intake and central obesity is less well studied. Generally, a low-fat diet may be at least harmless for insulin action in healthy adults (56, 57). However, two short-term weight loss programs in obese subjects, who may have been diabetic, reported that a high-fat diet was more beneficial to insulin sensitivity than an extreme low-fat diet (54, 58).