Risk of the development of Type 2 diabetes in relation to overall obesity, abdominal obesity and the clustering of metabolic abnormalities in Japanese individuals: does metabolically healthy overweight really exist? The Niigata Wellness Study

AIMS: We investigated the risk of developing diabetes across various metabolic phenotypes by considering the presence of overall adiposity or abdominal adiposity and the number of metabolic abnormalities and aimed to clarify whether a 'healthy overweight' phenotype, that is, overweight with no metabolic abnormalities, was protective of the development of diabetes. METHODS: We studied 29 564 Japanese individuals without diabetes. The 5-year incidence of diabetes was assessed according to a combination of either overweight (BMI ≥ 25.0 kg/m(2) ) or abdominal obesity (waist circumference ≥ 90 cm in men and ≥ 80 cm in women) and the number of metabolic factors present (hypertension, elevated triglyceride concentration, low HDL cholesterol concentration and impaired fasting glucose). RESULTS: A total of 1188 individuals developed diabetes. Compared with normal weight individuals with none of the four metabolic abnormalities, in overweight individuals with none of the four abnormalities there was an odds ratio (OR) of 2.32 [95% confidence interval (CI) 1.50, 3.59] for diabetes; having any one metabolic abnormality increased the risk of developing diabetes among normal weight individuals [OR 3.23 (2.55, 4.10)] and overweight individuals [OR 5.00 (3.77, 6.63)]. Among overweight individuals, the presence of impaired fasting glucose alone substantially elevated the risk of diabetes by 8.98-fold (5.52, 14.6) in comparison with the absence of the four metabolic factors. CONCLUSIONS: Being 'healthy overweight' was associated with a higher OR of developing future diabetes among Japanese individuals than normal weight individuals with no metabolic abnormalities, and being overweight with one or more abnormalities had a further elevated OR compared with 'healthy overweight' people.