Obesity-related risk factors of cardiovascular disease.

etabolic syndrome (MetS) is a known risk factor of diabetes and cardiovascular disease (CVD). However, in 2005, the American Diabetes Association and the European Association for the Study of Diabetes jointly stated that no existing definition of MetS meets the criteria to classify it as a syndrome and there have been endless debates on the pros and cons of how to diagnose the syndrome. Dichotomous diagnosis may often cause misleading effects on CVD risk assessment for individuals.1 The criterion that regards obesity as an inevitable component of MetS has a serious pitfall because there are a substantial number of metabolically obese, normal-weight individuals and only approximately one-third of the most insulin-resistant individuals are actually obese.1 An essential drawback of the Japanese MetS (“visceral fat syndrome”)2 is that it regards subcutaneous adipose tissue (SAT) as a protective factor against the morbid effect of visceral adipose tissue (VAT) and ignores the important risk contribution of abdominal SAT. When correlations of VAT volume and SAT volume were compared with metabolic risk factors and markers of inflammation, oxidative stress and endothelial dysfunction in the Framingham Heart Study, it was clearly shown that the risk contribution of SAT cannot be ignored.3,4 As for the risk of coronary artery disease, the standardized odds ratios of VAT area, SAT area, body mass index (BMI) and waist circumference for coronary calcification detected by electron-beam computed tomography, which is considered as an early manifestation of coronary artery disease, were 1.9, 2.0, 2.2 and 1.9, respectively, in men and 1.8, 1.9, 1.9 and 2.0, respectively, in women.5 Thus, VAT area is not superior to SAT area, BMI, or waist circumference as a risk factor of coronary artery disease, although the superiority of VAT area to other obesity indices is the original reason for proposing “visceral fat syndrome”.2 As for insulin resistance, Reaven reviewed the world literature comparing VAT area with SAT area and concluded that the correlations of VAT area and SAT area to insulin resistance are not statistically different.1 Koutsari and Jensen showed that free fatty acid (FFA) released by VAT contributes to only a small percentage of systemic FFA delivery and that upper-body SAT is the dominant contributor to circulating FFA, which is an important causal factor of peripheral insulin resistance.6 Japanese MetS and the MetS defined by the International Diabetes Federation (IDF) criteria, in which obesity is an inevitable component of MetS, were already shown to be inferior to the MetS defined by revised NCEP criteria in which obesity is not an inevitable component of MetS as a predictor of CVD in Japanese people.7,8