Excess body fat in obese and normal-weight subjects

Abstract

Excess body adiposity, especially abdominal obesity and ectopic fat accumulation, are key risk factors in the development of a number of chronic diseases. The advent of in vivo imaging methodologies that allow direct assessment of total body fat and its distribution have been pivotal in this process. They have helped to identify a number of sub-phenotypes in the general population whose metabolic risk factors are not commensurate with their BMI. At least two such sub-phenotypes have been identified: subjects with normal BMI, but excess intraabdominal (visceral) fat (with or without increased ectopic fat) and subjects with elevated BMI (. 25 kg/m 2 ) but low visceral and ectopic fat. The former sub-phenotype is associated with adverse metabolic profiles, while the latter is associated with a metabolically normal phenotype, despite a high BMI. Here, examples of these phenotypes are presented and the value of carrying out enhanced phenotypical characterisation of subjects in interventional studies discussed.

The Answer to Why Some Are Obese but Healthy?!

“…Furthermore, excess accumulation of ectopic fat in liver, skeletal muscle, and pancreas is known to contribute to metabolic disturbances [67]. For example, Ogorodnikova and his co-workers have reported that MHO women had intermediate levels of epicardial, pericardial and hepatic fat as compared to lean healthy and MUO women and were associated with insulin resistance [68].…”

Body Fat MRS

“…Indeed, a whole body 1 H MRS can be obtained in <1 second, leading generally to a spectrum consisting of just 2 peaks: water at 4.7 ppm and fat at 1.3 ppm, and the resulting analysis is simply their ratio, Figure 3. Compared to a whole body MRI scan, which requires significant analysis time (>30 mins), 1 H MRS of large data sets, with its rapid acquisition and analysis, becomes extremely attractive.…”

“…To date there have been several validation studies of this technique on mice 19 and rats 21 , where body fat content measured using whole body 1 Thus, caution must be taken in interpreting the fat/water ratio obtained by 1 H-MRS, as changes in the fat content detected by this technique may be a consequence of real variations in fat content -or simply reflect changes due to increases in tissue hydration or edema. Interestingly, the very difference between MRS and MRI outputs could in theory be utilized to assess changes in AT hydration, although interpretation of the results may not be straight forward.…”

“…Conventional methodologies include indirect methods based on anthropometry (body mass index, BMI; waist and hip circumference), skin-fold measurements, bioelectrical appearance, underwater weighing and air plesmography, while more direct methods include imaging technology such as computer tomography/dual-energy-X-ray absorptiometry (CT/DXA) and magnetic resonance imaging (MRI) 1 . While MRI has become the gold standard for measuring body fat content and distribution 2 , the large number of images generated, particularly from whole body scans, together with the lack of fast, affordable and automated methods of analysis, has driven the search for faster more efficient methods of data acquisition and analysis.…”

Fat-Referenced MRI: Quanitaive MRI for Tissue Characterizaion and Volume Measurement

“…Central obesity measurments (such as waist circumference) are less influenced by the amount of LT, and more sensitive to the VAT-SAT distribution. However, within the range of normal waist circumferences there is still large variations in the VAT-SAT distribution, as has been demonstrated by Thomas et al [9]. There are many benefits of more accurate and precise body-composition methods, as they would allow more sensitive diagnosis and monitoring of intervention effects.…”