It is the metabolic activity of visceral fat packed around abdominal organs that determines most of the harmful consequences of being overweight, not the subcutaneous fat deposits elsewhere in the body. Excess visceral fat produces chronic inflammation through a variety of mechanisms, such as increased burden of senescent cells, cell signaling that mimics the signals of infected cells, and more cell debris that triggers the immune system into overactivity. That chronic inflammation in turn disrupts normal tissue maintenance and cell behavior, and drives the onset and progression of all of the common age-related conditions. It is fair to say that being overweight literally accelerates aging, and the more visceral fat, the larger the effect.
Two recent comprehensive meta-analyses assessed the association of general adiposity, represented by body mass index, with the risk of all cause mortality in the general population. The results indicated that a U shaped and a J shaped association existed between body mass index and the risk of all cause mortality in the general population. The lowest risk was observed for a body mass index of 22-23 in healthy never smokers. Body mass index is easy to obtain and so is the most frequent anthropometric measure used to investigate obesity-mortality and obesity-morbidity associations.
The validity of body mass index as an appropriate indicator of obesity has been questioned. Research suggests that body mass index does not differentiate between lean body mass and fat mass; therefore, when using body mass index as a measure, inaccurate assessment of adiposity could occur. Additionally, the most important limitation of body mass index is that it does not reflect regional body fat distribution. Existing evidence suggests that central obesity and abdominal deposition of fat is more strongly associated with cardiometabolic risk factors and chronic disease risk than overall obesity.
Taking this evidence into account, indices of central obesity might be more accurate than body mass index when estimating adiposity, and therefore could be more closely and strongly associated with the risk of mortality. We aimed to perform a systematic review and dose-response meta-analysis of prospective cohort studies to investigate the association of indices of central fatness with the risk of all cause mortality in the general population, in never smokers, and in healthy never smokers. The indices of central fatness were waist circumference, hip circumference, thigh circumference, waist-to-hip ratio, waist-to-height ratio, waist-to-thigh ratio, body adiposity index, and A body shape index.
Indices of central fatness including waist circumference, waist-to-hip ratio, waist-to-height ratio, waist-to-thigh ratio, body adiposity index, and A body shape index, independent of overall adiposity, were positively and significantly associated with a higher all cause mortality risk. Larger hip circumference and thigh circumference were associated with a lower risk. The results suggest that measures of central adiposity could be used with body mass index as a supplementary approach to determine the risk of premature death.