Abstract
<b><i>Introduction:</i></b> Few studies have investigated the association between frailty and subsequent body composition. <b><i>Methods:</i></b> We performed separate linear mixed model analyses to study the associations between changes in the participant frailty status assessed by a frailty index (FI) and subsequent body mass index (BMI), lean mass index (LMI), fat mass index (FMI), and FMI to LMI ratio values assessed on three occasions over 17 years. The analyses were carried out among 996 participants spanning from age 57 to 84 years. <b><i>Results:</i></b> With advancing age, LMI and BMI decreased, whereas FMI and FMI to LMI ratio increased. Participants with “stable frailty,” followed by those with “increasing frailty” experienced faster decreases in LMI and faster increases in FMI and FMI to LMI ratio values from midlife into old age relative to those in the group “stable not frail.” Contrastingly, those in the highest third of absolute annual increase in FMI and FMI to LMI ratio became more frail faster from midlife into old age relative to those in the lowest third. <b><i>Conclusions:</i></b> We found evidence of an adverse health outcome of frailty where lean indices declined faster and fat indices and fat-to-lean ratios increased faster from midlife into old age. The changes resembled those that occurred with aging, but at a faster pace. The relationship between body composition and frailty is likely bidirectional, where high or increasing levels of fat are associated with the risk of becoming more frail earlier, but where a longer duration of frailty may increase the risk of faster age-related changes to body composition.