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Usage of BMI
The body mass index (BMI) is the currently recommended fat-related biomarker for identifying individuals at elevated risk of cardiovascular disease, type 2 diabetes, and all-cause mortality. This indicator also serves as a classification tool for obesity.
However, a study published in the Journal of the American College of Cardiology has found that if we were to evaluate critically the performance of BMI as a biomarker, it would fall short in several areas.
This 6-year follow-up study of 1,106 participants found that higher volumes of abdominal fat, especially visceral fat, are associated with a worse cardiovascular risk profile above and beyond risk prediction based on BMI or waist circumference alone.
The researchers suggest that abdominal fat distribution, as measured by computed tomography (CT) scanning, is more predictive of a patient's cardiovascular risk than his/her body mass index (BMI) or waist circumference.
BMI measurement is part of the Framingham risk score assessment, which is a test that is based on the Framingham observational study from the 1940s on health parameters linked to cardiac events.
The research also found that changes in abdominal fat volume and density seemed to correlate to variations in other cardiovascular risk factors, including hypertension and unbalanced blood lipids or cholesterol.
CT-based body composition analysis
If researchers are correct, this may mean that there is such a thing as "favourable" fat distribution whereby fat is benign in some parts of the body, while harmful in others.
Taking two obese individuals with the same BMI as example, the one who tends to have more visceral fat (around internal organs), a fatty liver, and skeletal muscle fat will have higher disease risks than his peer only carrying excess subcutaneous fat.
Similarly, there are different fat compositions for the same waist circumference. In other words, a large waist circumference may only reflect an increase in subcutaneous abdominal fat without giving any indication as to how much intra-abdominal fat—which is a marker of visceral fat—there is.
CT-scans or MRIs can locate and measure this pretty accurately. In this study, participants underwent CT measurement of abdominal fat volume, encompassing both subcutaneous fat and visceral fat, and their density.
The results revealed that increases in visceral fat increased other cardiovascular risk factors, such as hypertension, high cholesterol levels, high triglycerides, and metabolic syndrome (which is associated with obesity), more so than increases in subcutaneous fat.
This highlights the importance of taking into account quantitative, qualitative as well as the location aspects of fat tissue when assessing, along other factors, a patient's heart disease risk.
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© 2022 Camille Bienvenu