Body composition and mortality in the general population: A review of epidemiologic studies

Numerous studies have examined the association between body mass index and mortality and often observed that risk of mortality was higher in those with lower body mass index than those who were overweight or even obese (“obesity paradox”). One potential explanation of the obesity paradox is the limitation of body mass index as an imperfect measure of adiposity. However, relatively few studies have examined the association between body composition and mortality due to practical issues of assessing body composition in large-scale epidemiological settings. The available epidemiologic studies on this topic were heterogenous with regard to study design, analyses, results, and interpretations. The majority of studies using direct body composition measures such as dual-energy x-ray absorptiometry or computed tomography had relatively small sample size, short follow-up period and restricted study population. Studies have also used other approaches to indirectly estimate body composition to examine the association with mortality in a larger and more representative population. Overall findings were not consistent but suggested that fat mass and lean body mass may play an independent role on mortality in the general population. Various shapes of the associations were observed, but studies generally suggested that high fat mass was associated with increased risk of mortality (especially higher range of fat mass) and low lean body mass was associated with increased risk of mortality (especially lower range of lean body mass). On the other hand, fat mass and lean body mass tended to show either null or inverse association with mortality in elderly populations. Given the complex relationship of two body components as well as with other factors (e.g., age, smoking, disease, etc.), future studies should be conducted and interpreted after careful consideration of potential biases. In summary, the available data suggest independent associations of fat mass and lean body mass on mortality in the general population. Impact statement: Current understanding of the association of body composition on mortality in the general population is limited. This review evaluated the available epidemiologic studies on body composition and mortality that leveraged diverse approaches to estimate body composition. Although studies showed inconsistent results, there was evidence suggesting that high fat mass and low lean body mass may be independently associated with mortality in the general population. This review may help partially explain the “obesity paradox” phenomenon and facilitate further studies to advance the understanding of the association of body composition on health in the general and patient populations.