Investigating the Heterogeneity in Regional Body Composition, Metabolic Risk and Response to Weight Loss Among Obese Men and Women

Abstract

While the excess accumulation of abdominal subcutaneous and visceral adipose tissue (abdominal SAT and VAT, respectively), is independently associated with increased health risk, the relative amount of lower body SAT is associated with an improved health profile. In contrast to the established metabolic benefit of reducing VAT and abdominal SAT, the first study in this thesis investigated whether loss of lower-body SAT during diet and/or exercise induced weight-reduction resulted in a deterioration of metabolic profile in a sample of obese men (n = 58) and women (n = 49). After control for potential confounders, reductions in VAT, abdominal and lower body SAT were all associated with improvements in certain metabolic risk factors. However, only reductions in VAT and abdominal SAT remained associated with improvement in risk factors independent of changes in other AT depots. Recently, it was suggested that a large breast size among women may predict type-II diabetes risk independent of body mass index (BMI) and waist circumference. While the mechanism is unknown, a large breast size may predict health risk by indicating fat deposition in ectopic depots such as VAT or inter-muscular AT (IMAT). The second study investigated the independent associations between breast volume with metabolic risk and regional fat distribution in 92 overweight or obese premenopausal women. Although breast volume was not significantly associated with metabolic risk, after control for age, BMI and waist circumference level, women with the highest breast volume had approximately 1.1 and 1.3 kg more VAT and IMAT, respectively, by comparison to women with the smallest breast volume. In contrast to the metabolic benefits of weight loss among metabolically-abnormal obese (MAO) individuals, weight loss among metabolically healthy obese (MHO) individuals may be unnecessary or even harmful. In the third study, 63 MHO and 43 MAO men and women participated in an exercise or diet weight-loss intervention. In response to similar weight loss, MHO and MAO men and women showed significant improvements in insulin sensitivity. However, significant improvements in other metabolic variables (triglycerides, fasting glucose, HDL-cholesterol, and total cholesterol) were only observed among MAO, but not MHO subjects.