Association of body-shape phenotypes with imaging measures of body composition in the UK Biobank cohort: relevance to colon cancer risk

Background: Body mass index (BMI), waist and hip circumference are strongly correlated and do not reflect body composition. A Body Shape Index (ABSI) and Hip Index (HI) define waist and hip size among individuals with the same weight and height and would thus reflect body density. We examined differences in body composition between body-shape phenotypes defined with ABSI and HI and used this information to propose explanations for associations between body-shape phenotypes and colon cancer risk. Methods: We used data from the UK Biobank Resource for 15,520 men, 16,548 women with dual-emission X-ray absorptiometry (DXA) measurements; 3997 men, 4402 women with magnetic resonance imaging (MRI) measurements; 200,289 men, 230,326 women followed-up for colon cancer. We defined body-shape phenotypes as: large-ABSI-small-HI ("apple"), small-ABSI-large-HI ("pear"), small-ABSI-small-HI ("slim"), large-ABSI-large-HI ("wide"). We evaluated differences in body composition in linear models and associations with colon cancer risk in Cox proportional hazards models adjusted for confounders and explored heterogeneity by BMI. Results: Among individuals with the same height and weight, visceral adipose tissue (VAT) was lowest for "pear" and highest for "apple", while abdominal subcutaneous adipose tissue (ASAT) was lowest for "slim" and highest for "wide" phenotype. In the gynoid region, differences between "apple" and "pear" phenotypes were accounted for mainly by fat mass in women but by lean mass in men. In men, lean mass was inversely associated with waist size, while the pattern of gynoid fat resembled ASAT in women. Lean and fat mass were higher for higher BMI, but not hand grip strength. Compared to normal weight "pear", the risk of colon cancer in men (1029 cases) was higher for "apple" phenotype for normal weight (hazard ratio HR = 1.77; 95% confidence interval: 1.16-2.69) and comparably for overweight and obese, higher for "wide" phenotype for overweight (HR = 1.60; 1.14-2.24) and comparably for obese, but higher for "slim" phenotype only for obese (HR = 1.98; 1.35-2.88). Associations with colon cancer risk in women (889 cases) were weaker. Conclusions: ABSI-by-HI body-shape phenotypes provide information for body composition. Colon cancer risk in men appears related to ASAT quantity for "slim" and "wide" but to factors determining VAT accumulation for "apple" phenotype.