Studies in the estimation of body fat and body fat changes in man
The aim of this work was to compare magnetic resonance imaging (MRI), and 3-(TCM) and 4-compartment (FCM) models for the estimation of body fat and changes in fat mass (FM) in man. FM was estimated in 10 obese women by MRI and a TCM based on underwater weighing (UWW) and body water dilution (D2O) at the start and end of a 21 day residential weight reducing regimen. Mean (SEM) MRI estimates of FM before weight loss were 3.19 (0.25) kg below values from TCM, however, FM change over the 21 days by MRI agreed well with TCM. In 8 women, intra-abdominal (IAT), subcutaneous (SAT) and total (TOT) adipose tissue area was calculated from MRI at 2,9 and 9 sites respectively. Mean (SEM)% reductions were 14.0 (12.0)% (p<0.01); 8.2 (2.0)% (p<0.0001) and 11.8 (2.5)% (p<0.0001) respectively. In another series of studies, FM was estimated by 2-compartment methods: UWW, D2O, dual energy X-ray absorptiometry (DXA), skinfold thickness, bioelectrical impedance; TCM and a 4-compartment method (FCM) based on UWW, D2O and DXA in 28 women [16 non-obese (NW), 12 obese (OW)] and 19 men [13 non-runners (NM), 6 runners (MR)]. Estimates of FM by the 2-compartment methods agreed more closely with TCM and FCM than with each other. Agreement with FCM was best in NM and worst in OW. No difference was found between fat mass estimated by TCM and FCM in men. Average density of the fat free mass (FFM) was 1.113 (NW), 1.112 (NM), 1,106 OW, 1.106 (MR) g/ml. Hydration of the FFM was 0.743 (OW), 0.717 (MR), 0.713 (NW), 0.700 (NM). MRI has considerable potential as a method for estimating body fat and provides information on adipose tissue distribution. Multi-compartment methods appear to reduce errors in the FM estimated by 2-compartment methods.