Research Project Introduction
Excess body fat is a major cause of diabetes, heart attacks and strokes, worldwide. Body-mass index (BMI; defined as weight in kilograms divided by height in meters squared) is the basis of the World Health Organisation’s definition of overweight and obesity, with a BMI of between 25 and 30 kg/m2 classified as overweight, and over 30 kg/m2 as obese. However, there is increasing evidence that levels of body fat for a given BMI may vary between populations, raising questions regarding universally applied BMI-based guidelines for overweight and obesity. Although BMI is frequently used in Malaysia to assess excess body fat, there have been no large-scale imaging studies with direct measurements of body fat and its distribution which would allow us to understand better the relationship between body composition and disease outcomes in this population.
From 2006-2012, The Malaysia Cohort study – initiated by the Malaysian government – recruited 106,527 adults aged 35 years or over. Participants completed a lifestyle questionnaire, underwent physical measurements, provided a blood sample and are now being followed for health events. In 6000 of The Malaysia Cohort participants, we will conduct whole body Dual-energy X-ray Absorptiometry (DXA) imaging (which provides data on body fat distribution in addition to body fat percentage) using protocols established by the UK Biobank (a large cohort study co-ordinated by the Nuffield Department of Population Health, University of Oxford). This imaging sub-study will significantly enhance this national biomedical resource.
Using DXA imaging, this study will reliably assess the relationship between conventional measures for estimating body composition (including BMI, waist circumference and waist-hip ratio) with the absolute regional fat masses derived from the DXA measurements in the Malaysian population. It will then assess the relationship between these measures and risk of diabetes and cardiovascular disease, to inform public health guidance on the appropriate measure of excess body fat in this population, the ideal ‘normal’ range of these measures, and whether guidance should vary for the different ethnic groups in Malaysia. DXA imaging will also significantly enhance the potential of The Malaysia Cohort to investigate the genetic and environmental determinants of obesity in Malaysia, and the biological pathways through which it causes diabetes and cardiovascular disease.
Not all people who are overweight or obese suffer adverse consequence from their excess weight, in part due to differences in fat distribution. Indeed, as recently reported from The Malaysia Cohort, the prevalence of obesity (based on BMI) and type 2 diabetes is very divergent between the major ethnic groups in Malaysia (Malay, Indian and Chinese) and this is only partly explained by BMI. Therefore, a better understanding of the between-ethnic group risk, based on tissue and organ-specific fat depots, will enable more precise targeting of limited resources to those who will gain the most benefit.