The IDEA study: From kilos and metres squared to centimetres and mmol/l

As an anthropometric marker of abdominal obesity, an elevated waist circumference is gaining recognition as a risk factor for type 2 diabetes and cardiovascular disease (CVD) 1-3. However, some still debate whether measuring the waistline is feasible in clinical practice and whether this measurement adds to the information provided by an index of relative weight such as body mass index (BMI, or the ratio of weight in kg over height in m2) 4-6. In view of evidence that an elevated waistline increases the risk of diabetes and coronary heart disease at all BMI values 7, 8, the recently published IDEA study provides compelling evidence that waist circumference can be measured by physicians and that it adds to the information provided by BMI 9.

IDEA is a simple epidemiological study that is huge in scope. It was conducted in 63 countries and involved more than 6,400 primary care physicians who received video training on how to properly measure the waist circumference of their patients evaluated on two separate half days. Physicians were asked to measure their patients’ weight, height, and waist girth and report on their clinical status. The study yielded information on the BMI and waist circumference of about 100,000 women and 70,000 men, allowing the relationship of these indices with diabetes and CVD to be examined. The results were remarkably straightforward. First, prevalence of obesity was found to be quite high among patients seen by primary care physicians all over the world, although regional differences were noted. Second, there was a continuous relationship between waist circumference and the prevalence of diabetes and CVD in both men and women. Thus, no evidence for a waist girth threshold could be found. Third, both BMI and waist circumference were tied to diabetes and CVD. Finally and most importantly, an elevated waist circumference raised the risk of diabetes or CVD at any BMI value. The conclusions to be drawn from this study are very clear-cut. A key finding is that primary care physicians can measure waist circumference if they are shown how to do it properly. In addition, measuring waist circumference further refines the risk associated with any given BMI. It is therefore feasible to measure waist circumference as doing so provides physicians with valuable additional information and helps them better evaluate the risk associated with overweight and obesity.

Finally, it has been argued that excess intra-abdominal (visceral) fat accumulation is behind the risk associated with an elevated waistline 10-13. However, not every patient with an elevated waistline is intra-abdominally obese. Some very obese patients simply have too much subcutaneous fat. In order to distinguish between an elevated waist girth caused by excess intra-abdominal vs. subcutaneous fat, increased plasma triglyceride levels have been suggested a marker of the inability of subcutaneous adipose tissue to act as a metabolic sink 14,15. If waist circumference is elevated, hypertriglyceridemia could then be a simple metabolic marker that the patient may be intra-abdominally obese and at increased risk of diabetes and CVD. In this regard, a recent paper published by Lemieux et al. 16 reviewed the evidence that it may be more useful to consider centimetres of waist circumference and mmol/l of triglycerides rather than measure kilos of body weight and the patient’s height.


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