Abdominal fat changes more important to predict cardiovascular risks than BMI

A new analysis, based on the Framingham Heart Study, has found that fat distribution 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, a test that is based on the Framingham observational study, which started in the 1940s and measured health parameters that tend to correlate with the number of heart attacks seen then.
This 10-year risk prediction test is in effect widely used in the UK today by physicians as a first line cardiovascular risk check for patients. It sets out to determine predispositions to heart disease by looking at a person’s diabetes history, BMI, total cholesterol levels, blood pressure, and smoking habits.
In this new study, however, researchers question the value of assessing risks with BMI.
They suggest that higher volumes of abdominal fat, and especially visceral fat, are associated with a worse cardiovascular risk profile above and beyond risk prediction based on BMI or waist circumference.
Changes in abdominal fat volume and density also lead to variations in other linked cardiovascular risk factors, including hypertensio, an unhealthy balance of cholesterol, and elevated triglycerides.
These findings, published in the Journal of the American College of Cardiology, come after a 6-year follow-up study of 1,106 participants of the Framingham study’s third generation cohort.
The study’s lead author, Dr Jane J Lee, from the National Heart, Lung, and Blood Institute in Massachusetts, and her colleagues are making a case for imaging fat volume and quality to give important clues to cardiometabolic risk that BMI may miss.
A high BMI can sometimes send mixed messages and therefore isn’t always a measure of heart disease.
In fact, previous research has shown that, in less common cases, some obese adults have a perfect or near perfect cardiometabolic risk score (the count of risk factors exceeding recommended thresholds) of 0 or 1, due in part to favourable fat distribution.
Fat may be benign in some parts of the body, while harmful in others. Comparing two obese individuals with the same BMI, 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. A high 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, is there.
CT-scans or MRIs can locate and measure this “bad fat” pretty accurately. In the current study, the participants underwent CT measurement of abdominal fat volumen, encompassing both subcutaneous fat and visceral fat, and their density.
The results revealed that increases in visceral fat drove other cardiovascular risk factors, such as hypertensio, high cholesterol levels, high triglycerides, and metabolic syndromen, higher than increases in subcutaneous fat did.
Overall, this study highlights the importance of quantitative and qualitative aspects of fat tissue for assessing a patient’s heart disease risk.