Investigating the relationships between body fat distribution, metabolic biomarkers and endocrine regulators in Pacific and New Zealand European women : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Nutrition and Dietetics, Massey University, Albany, New Zealand

Abstract

Background: The burden of overweight and obesity continues to rise throughout the world, including New Zealand (NZ). Obesity prevalence differs among ethnic groups in NZ and this is associated with considerable health inequities. For example, Pacific peoples living in NZ have higher rates of obesity‐related health issues, compared to NZ Europeans. Understanding the link between body composition and metabolic health is essential for the development of more effective preventative and intervention strategies for different population groups, who may have different metabolic disease risk profiles. Aims: This research aims firstly, to investigate metabolic biomarkers and endocrine regulators in two distinct groups of women with different body fat profiles (normal and obese) and of high metabolic disease risk (Pacific women) or moderate metabolic disease risk (NZ European women); and secondly, to compare different approaches of assessing body composition and fat distribution and their relationship with metabolic and endocrine profiles. Design: A cross‐sectional study conducted in 304 Pacific and NZ European women aged 18‐45 years. Anthropometry, a range of body composition and fat distribution measurement approaches, metabolic biomarkers (including lipids, markers of glucose metabolism and inflammation markers) and endocrine regulators (insulin and leptin) will be investigated. Outcomes: Total body fat percentage (BF%) measured by bioelectrical impedance analysis (BIA) correlated strongly with BF% measured by dual X‐ray absorptiometry (DXA). Waist‐to‐hip ratio (WHR) had weak associations with android fat percentage and BF% measured by DXA, whereas waist circumference (WC) and waist‐to‐height ratio (WHtR) performed better in this respect. Anthropometric measurements had similar correlations with total body fat percentage and regional fat depots for both ethnic groups. For each ethnicity, women in the high body mass index (BMI) group had higher circulating concentrations of fasting insulin, fasting glucose, glycosylated haemoglobin (HbA1c), triglycerides and total cholesterol to high‐density lipoprotein (TC/HDL) ratios, and lower circulating HDL cholesterol concentrations in comparison with the normal BMI group. Gynoid fat percentage had weak associations with circulating cardio‐metabolic risk factors, including low‐density lipoprotein cholesterol (LDL‐C), triglycerides, HbA1c, fasting insulin and fasting glucose concentrations. On the other hand, android and visceral fat percentages had stronger, positive associations with these cardio‐metabolic risk factors. Furthermore, BF% measured by DXA and BMI explained a similar amount (57.1% and 49.7% respectively) of the variance in leptin concentrations. Conclusion: Our findings suggest that in a New Zealand population with markedly different body fat profiles, assessment of WC, WHtR and BMI are effective tools for assessing adiposity and the associated cardio‐metabolic disease risk factors in a clinical setting, whereas WHR does not appear to be a useful tool. This thesis research provides strong evidence that these clinically important and effective tools should continue to be used in dietetic practice, across different population groups with different metabolic disease risks and different body fat profiles.