Abdominal fat is a better predictor of cardiovascular risk than body mass index

Does the press release accurately reflect the study?

“The key message is correct insofar as it refers to adding anthropometric waist measurements to improve the assessment of cardiovascular risk. At present, there is insufficient robust evidence in the literature to support replacing BMI with the waist-to-height ratio (WHtR), for example, in the assessment of cardiovascular risk.” Is the study of good quality? Are the conclusions supported by solid data?

“From my perspective, and delving into the pathophysiology of obesity, there is data supporting the conclusion that WC and WHR contain solid information to conclude that central adiposity alone causes the observed differences.” How does this study fit in with the existing evidence?

“Rather than studying mortality or a single specific event, the study examines nine cardiovascular and mortality outcomes in a population with a very large sample size. This supports the robustness of the results.” Are there any significant limitations to bear in mind?

“There are several limitations, some of which have been mentioned, whilst others have not been explored in great detail. For example:

• There is a lack of information on physical activity, diet and the genetics of obesity. Some types of obesity have a very significant genetic component.
• Waist circumference and WHR were measured only once, at a single point in time, and we do not know how they have changed over the course of the follow-up period or whether this may have influenced the results.
• The follow-up period was very long, and lifestyle habits spanning several generations were mixed together; cultural specificities and changes over time may have had an influence. For example, precisely for this reason, we do not place much faith in prediction models based on artificial intelligence, because from the outset the computer system assumes that patients’ living conditions remain the same throughout the virtual years analysed by the system. And in real life, that is not the case. Furthermore, we must not forget that BW and WHtR are indirect measures of central adiposity; they are not equivalent to directly quantifying visceral fat using imaging techniques.
• It is an observational study, with the inherent limitations of such designs: it is non-randomised and non-interventional.
• The WHtR is more sensitive than the WHR and the WC.”

What are the implications for the real world?

“This has a significant practical advantage: measuring waist circumference is inexpensive, and calculating the WHtR is just as quick as calculating BMI. Consequently, both the results and, increasingly, expert opinions support the routine incorporation of some measure of central adiposity into clinical assessment, particularly in cardiovascular prevention. The paper by the EASO supports this idea. That is also the final recommendation. We should not “replace BMI” for the time being, but rather “it is advisable to supplement BMI with a measure of central adiposity, particularly waist circumference”. There is still a lack of data to tell us whether reducing WHtR actually leads to improved health outcomes, for the simple reason that, in the management of obesity, everyone has traditionally focused on weight, and the incorporation of WHtR into this management is a relatively recent development. There has not been enough time. There is a study which supports the view that reducing WHtR by <0.53 improves cardiovascular risk parameters".

‘Your waistline matters more to your heart than your weight’ would be the headline. We have known for a long time that we need to look beyond body mass index.

This is a high-quality study and, whilst the findings come as no surprise, they reinforce our long-held view that, beyond body mass index, it is not total weight that matters, but rather where that weight is distributed and, above all, visceral fat – which we already knew to be the most metabolically harmful from a cardiovascular perspective. In my view, this study is quite good, as it covers 20 years and nearly 260,000 patients followed up for cardiovascular events; it tells us that we can reclassify each patient’s risk based on a parameter as simple as measuring waist circumference or the waist-to-hip ratio, which can easily be done in the doctor’s surgery using a tape measure. In addition to weighing the patient and calculating their body mass index, it is essential to measure waist circumference and the waist-to-hip ratio using a tape measure, and even to use advanced technology such as body composition analysis to reclassify risk.

Why? Because there are patients who are not obese – those of normal weight or who are overweight – who, due to high levels of abdominal obesity, are at greater risk of these nine major cardiovascular events identified in this study. Even in patients with a higher body mass index, classified as obese, but who do not have abdominal obesity – possibly because their weight consists of muscle rather than fat – we see that this cardiovascular risk decreases. Therefore, this study highlights something essential in medical consultations: assessing where the fat is located. Doing so in a straightforward manner can save lives, as we can reclassify risk and treat people who might otherwise have been considered safe because they were of normal weight, yet had a high cardiovascular risk. Beyond weight, abdominal fat can reveal the true, hidden cardiovascular risk.

In summary, in my view, this is highly relevant and important. Our waist circumference (abdominal fat) reveals the true, hidden cardiovascular risk. The scales alone are not enough; it is essential to know not only body weight but also body composition, specifically abdominal fat (AF), which is more harmful to our heart.
Thus, the study reclassifies people who appear healthy based on their BMI (normal weight and overweight) but who, depending on their abdominal fat (measured by waist circumference), have a high risk of suffering cardiovascular events (heart attack, stroke or heart failure: 15 per cent and 50 per cent respectively). Conversely, the study found that 45 per cent of people with obesity have a low waist-to-hip ratio, which is associated with a lower cardiovascular risk than would be expected for their weight.

The press release does indeed reflect the findings, but in reality it says nothing new: the waist-to-height ratio (WHR), when combined with BMI, appears to be a better predictor of cardiovascular risk.

The implications for clinical practice are very clear. Measuring waist circumference is cheap, quick and feasible in primary care, preventive cardiology, endocrinology and internal medicine. It is not a question of abandoning BMI, but of complementing it. When assessing cardiovascular risk, particularly in primary prevention, we should pay more attention to where fat accumulates, not just to how much a person weighs.

The main limitation is that, as the press release also notes, complete information on physical activity, diet or genetic risk was not available – factors that can influence both adiposity and cardiovascular risk. Furthermore, waist circumference and the waist-to-hip ratio were measured only once, so we do not know how changes over time affect risk. Even so, these limitations do not invalidate the main message: BMI should not be used as the sole measure of cardiometabolic risk.

On the other hand, in clinical practice, we are quite clear about the need to use BMI and body fat index (BFI) in all clinical assessments and to evaluate the risk of obesity. This is not the case for the waist-to-hip ratio, as the measurements are too variable for clinical use.