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Body mass index, BMI, is not a reliable indicator of overall fitness for obese individuals as assessed by internal, or visceral, fat. An MRI and NMR study reveals that fat accumulation in different parts of the body, such as around the heart and the aorta and within the liver, is associated with decreased heart function, but BMI offers no correlation for this problem.
; r; X5 o- d2 l9 {# A. m. t8 jObesity is a growing problem in the developed world. Recent estimates suggest that almost a third of the US adult population is clinically obese and many more are chronically overweight. One defining measure of obesity is the body mass index, BMI. This figure is obtained by dividing a person's weight in kilograms by the square of their height in metres. It is intended to provide individuals with an indicator of where they lie in the spectrum from underweight to normal through to overweight and obese. 7 ?+ B, Z3 U( w6 Q. l/ v
There are, however, several problems with BMI as a health indicator is it does not take into account muscle mass versus fat tissue for instance or the loss of height one experiences after spinal injury or through aging. More importantly, however, it does not provide any insights into the type of fat accumulation present nor where that fat is located in the body. "BMI is a useful metric across the entire population," emphasises Ruberg, but, "it has limitations." / v' g8 Z! u8 J- W4 g @
Past studies have shown that fat accumulation in the liver and around the heart are linked to cardiovascular disease and type 2 diabetes. To which BMI says nothing.
3 w- P+ w( P q/ l* _, ?Now, Frederick Ruberg, Zhongjing Chen, Ning Hua, Sherman Bigornia, Zifang Guo, Kevin Hallock, Hernan Jara, Michael LaValley, Alkystis Phinikaridou, Ye Qiao, Jason Viereck, Caroline Apovian, and James Hamilton of Boston University School of Medicine (BUSM) have shown that fat collection in different body locations, such as around the heart and the aorta and within the liver, are associated with certain decreased heart functions. Their study, which is published online in the journal Obesity, also shows once again that measuring a person's body mass index is a wholly inadequate health metric and does not reliably predict the amount of undesired fat in and around these vital organs.
6 N: @& M" F$ c& SThe team determined fat volumes in obese people (defined by a BMI of more than 30). These volunteers all had raised blood pressure (hypertension) and/or diabetes. They compared the data with that obtained from lean, healthy individuals (who had an average BMI of 22). Magnetic resonance imaging (MRI) and proton MR spectroscopy were used to quantify pericardial and peri-aortic lipid volumes, cardiac function, aortic compliance and intra-hepatic lipid content. The team also measured fasting plasma lipoproteins, glucose, insulin, and free fatty acids for the volunteers.
8 u. Z2 x% K9 p' [The study found fat collections in anatomically separate locations, such as within the liver and around the heart. The accumulation of fat here was more strongly associated with problematic cardiovascular function, such as a decrease in cardiac pumping function. This effect could be an important factor for assessing an individual's health that is simply sidestepped by the BMI.
: @2 h' Q* c% C p( [: `/ \"Our study found that fat collection around the heart, the aorta and within the liver is clearly associated with decreased heart functions and that an MRI can quickly and noninvasively measure fat volume in these areas. Our study also found that looking at BMI of the individual does not reliably predict the amount of undesired fat in and around organs," says Hamilton, senior author and professor of biophysics, physiology and biomedical engineering at BUSM.
; o" h# t8 J; Q2 w1 D! ZThe researchers point out that this method of measuring cardiac function and fat deposits can be carried out in less than one hour and may provide a basis for future individualized treatment for clinically obese individuals with significant health problems. "While it is presently unclear how or if lipid storage in these depots is similarly regulated, the role these depots play in the development of insulin resistance and metabolic syndrome is the subject of significant ongoing scientific scrutiny," they add.
. ~% P' { t" t"We are suggesting that among obese individuals, BMI itself does not appear to predict accurately the distribution of fat in ectopic sites - the importance of which we are beginning to understand," Ruberg told spectroscopyNOW. # h2 D U4 v+ v" [2 Q+ e+ {8 B
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Fat testing is more than skin deep, MRI beats pinch-an-inch
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发表于 2009-12-28 12:34:19
