Associations of body fat and inflammation with non-communicable chronic diseases and mortality: A prospective cohort study
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Introduction
Certain leading medical organizations are considering alternatives to the body mass index (BMI) as a predictor of the risk for non-communicable chronic disease (NCD) or death. Our objective was to evaluate the associations between various measures of body fat and the risk of incident NCDs or mortality, independent of inflammation.
Methods
This was a population-based prospective cohort study (the UK Biobank cohort) set in the United Kingdom. The participants (between 40 and 69 years) accrued between March 2006 and October 2010, and followed until December 2022. The exposures were BMI, waist:hip ratio (WHR), bioimpedance analysis-measured body fat (fat BIA ), C-reactive protein (CRP) and various other measures of body fat obtained by dual-energy X-ray absorptiometry (including visceral adipose tissue) and magnetic resonance imaging. The outcomes were all-cause death, cardiovascular disease (heart failure, hypertension, myocardial infarction, pulmonary embolism, and stroke), cancers (breast, colorectal, endometrial, esophageal, kidney, ovarian, pancreatic, and prostate), diabetes, asthma, gallbladder disease, chronic back pain, and osteoarthritis.
Results
There were 500,107 participants: the median age was 58 years (interquartile range 50-63) at baseline and 45.6% were male. The 5 th and 95 th %iles for measures of body fat were: BMI 20.5 (considered “healthy”) and 37.0 kg/m 2 (considered “unhealthy”), WHR 0.71 and 0.94, BIA 24.8 and 47.6% in females, and in males BMI 22.0 (considered “healthy”) and 35.4 kg/m 2 (considered “unhealthy”), WHR 0.83 and 1.05, BIA 15.5 and 34.7%. BMI was strongly correlated to fat BIA (0.85 in females, 0.80 in males) but less so with WHR (0.46 in females, 0.59 in males).
All measures of body fat were positively associated with the incidence of NCDs but only WHR remained positively associated with death after full adjustment (HR 95 th %ile vs 5 th %ile [95%CI]: BMI 0.80 [0.76,0.84], WHR 1.21 [1.16,1.28], BIA 0.80 [0.76,0.84] in females; BMI 0.89 [0.85,0.93], WHR 1.19 [1.14,1.24], BIA 0.89 [0.85,0.92] in males). Simpler models that adjusted for age, sex, CRP, WHR and either BMI or fat BIA gave similar results. Associations between body fat and the incidence of NCDs after accounting for the competing risk of death were also similar.
Conclusion
BMI was strongly correlated with fat BIA , but WHR and VAT DXA were less so. All measures of body fat were associated with the incidence of NCDs but only WHR was independently associated with mortality. These findings support the hypothesis that body fat may be protective against death, and that the excess risk associated with higher WHR may be mediated by something other than body fat.
Key Questions
What is already known about this topic?
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Obesity as measured by body mass index is associated with chronic disease but less so with mortality.
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Less is known about alternative measures of body fat.
What this study adds?
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Body mass index is strongly correlated with body fat as measured by bioimpedance analysis, but less so with the waist:hip ratio and visceral adipose tissue.
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All measures of body fat were associated with the incidence of chronic disease but only the waist:hip ratio was independently associated with mortality.
How this study might affect research, practice or policy?
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These findings support the hypothesis that body fat may be protective against death, and that the excess risk associated with higher waist:hip ratio may be mediated by something other than body fat.
