Waist-to-Height Ratio Plus BMI Identifies Obese at Highest CVD Risk

June 02, 2014

SOFIA, Bulgaria — A new study has shown that combining 2 ways of assessing a person's size — body mass index (BMI) and waist-to-height ratio (WHtR) — may be a better way of identifying which overweight and obese individuals are at highest risk for cardiovascular disease and diabetes than either measurement alone.

The work was reported at the 2014 European Congress on Obesity during a hot-topic presentation by Seán Millar, PhD, an epidemiologist at University College Cork, Ireland.

Dr. Millar said that the concept of being obese and "metabolically healthy" is a controversial idea at a population level, "and we would never advocate that any level of obesity is necessarily healthy or okay."

But "at a clinical level, we have to acknowledge that a high proportion of subjects who are overweight or obese will not develop cardiometabolic outcomes, so we are looking for tools to identify the people who will.

"If the prevalence of obesity in our population is high, we run the risk of just classifying everyone as being at risk, so we're looking to narrow it down," he added.

Margaret Ashwell, PhD, a former science director of the British Nutrition Foundation and long-time proponent of the WHtR, agrees but argues that the latter measure is all that is strictly necessary.

" 'Is the waist-to-height ratio greater than 0.5?' is the easiest, quickest screening tool you can have, and it works for everybody in the world, and it's particularly useful for children," she noted. Also, eliminating BMI from the equation will make the assessment quicker and easier for doctors, as they won't have to weigh people, she explained.

Nevertheless, she acknowledged that many people are wedded to BMI, "so it's better to add WHtR than not to add."

The Rationale for Combining BMI With WHtR

Dr. Millar explained that BMI is the traditionally assessed surrogate measure of adiposity, "but there are certain limitations with this. It's a weight-to-height measure that cannot distinguish between fat and lean mass, and numerous studies have suggested that obesity characterization based on BMI is inadequate and may misclassify adiposity."

Other research has shown that central obesity is more important, and this is often measured by waist circumference, he said, but the latter "doesn't take whole body fat distribution into account."

The WHtR has recently been proposed as a relatively new surrogate measure of obesity — consisting of the waist circumference divided by height — and "has certain advantages," he noted (Obes Rev. 2012;13: 275-286). "As a ratio, it may allow us to have cut points that are similar for men and women and similar between ethnicities." But while numerous studies have suggested the WHtR is a better predictor of cardiometabolic outcomes, "the discriminatory differences are actually quite modest," he observed.

So he and his team decided to examine the predictive value of using both BMI and WHtR together.

They studied a sample of 2047 men and women aged 50 to 69 years from the Cork and Kerry Diabetes and Heart Disease Study who were recruited from a large primary-care center and represented a mix of urban and rural residents.

They calculated both BMI and WHtR in the participants and divided them into equal tertiles for each measurement, representing obese, overweight, and normal weight. The aim was to compare the metabolic profiles in subjects defined as overweight or obese by both indices and compare them with those deemed overweight or obese by just one index.

Multivariate adjustment was performed for alcohol use, smoking status, physical activity, age, and gender.

"Subjects who were classified as overweight by either BMI or WHtR on the whole displayed a cardiometabolic profile that, although increased, was not necessarily that dissimilar from people who we would classify as normal weight," Dr. Millar noted.

Narrowing Down the Risk: But How Easy Is It to Perform in Practice?

In the study, 881 subjects were classified as "high risk" by either measure, but using both BMI and WHtR together reduced this number to 680, a more than 20% reduction, said Dr. Millar.

And metabolic profiles "were less optimal in subjects defined by both indices, with distinctions in obese categories being most pronounced," he added.

In obese subjects within the highest BMI and WHtR tertile, the prevalence of high blood pressure, insulin resistance, cardiometabolic-feature clustering, and prediabetes was 81%, 55%, 34%, and 17%, respectively.

Calculating both indices "is certainly no harder than the equation for BMI — the only additional work is in assessing a person's waist circumference," Dr. Millar told Medscape Medical News.

But although there are apps to calculate BMI and WHtR, there isn't as yet an easy way to combine the 2, he acknowledged.

He said there are 2 potential uses for this new approach: it could be used as a public-health screening program, where subjects could measure their own waist circumference and height and weight and determine whether they might be at risk.

Or, from a clinical perspective, it could help focus resources on the early identification of those who should be prioritized for pharmacological and lifestyle interventions "and may also indicate what sort of blood tests a clinician might wish to perform.

"In the context of the increasing obesity epidemic worldwide, risk stratification using BMI and WHtR may provide a simple, noninvasive, cost-effective, and more accurate method for predicting those who are at high risk that might be useful in resource-poor situations or in populations without free access to primary healthcare."

Earlier targeted interventions can prevent people from developing type 2 diabetes and other cardiometabolic conditions, he concluded.

Dr. Millar reported no relevant financial relationships. His study was supported by a research grant from the Irish Health Research Board. Dr. Ashwell is an independent scientific consultant, and her clients include a number of food manufacturers listed on her website. She is also a member of the advisory board of the Global Stevia Institute.

2014 European Congress on Obesity. Abstract 696, presented May 31, 2014.


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