Watch your waist, redux

For years physicians and researchers have used Body Mass Index as a simple and cheap measure to help estimate an individual's risk of such chronic diseases as diabetes, high blood pressure, and heart disease. It's not perfect, however, as you probably know: those who are extremely fit and have very low body fat can still be classified as overweight or obese when you simply look at the interaction of weight and height.

This is why Waist to Hip Ratio is also important, as it serves as an indicator of the location of your body fat: those with a higher Waist to Hip Ratio are much more likely to be carrying fat around their middle, which often means around their internal organs. As we've seen, that visceral adiposity, as it is called, carries a much greater risk of disease than just carrying fat around one's waist. That said, Waist to Hip Ratio is not perfect, either: the best way to determine the location of one's body fat is through expensive and time-consuming body scans. Your local internist is hardly going to order such an expensive scan just to find out where your fat is, which is why smart physicians will use both Body Mass Index, Waist to Hip Ratio, and their personal knowledge of you and your overall lifestyle to advise you on your health.

A study just published in the Annals of Internal Medicine suggests that Waist to Hip Ratio is even more important than we may have thought (2015;163(11):827-835).

The authors made use of data gathered through NHANES III (Third National Health and Nutrition Examination Survey), the most recent set of NHANES data (initially gathered 1988-1994 and concluding in 2006) that includes both waist and hip circumference measures. Over 15,000 men and women with at least an 18.5 Body Mass Index (the minimum of what is considered to be normal weight) and no history of cancer other than skin cancer were included in their analysis.

The Body Mass Index and Waist to Hip Ratios of those participants who passed away before the conclusion of the study, along with their cause of death, were compared to the Body Mass Index and Waist to Hip Ratios of those who did not.

Somewhat unsurprisingly, those men whose BMI was in the normal range but had a Waist to Hip Ratio of .90 or greater (considered centrally obese by the World Health Organization) were 87% more likely to die of any cause than those men whose BMI and WHR were both in the normal range. In fact, they were more than twice as likely to die from any cause than a man whose BMI was in the clinically overweight range (25 to 30) but did not carry his weight around his middle.

The results were similar for women: those with a normal BMI but a WHR above .85 were 48% more likely to die of any cause than those women whose BMI and WHR were normal. They were as much as 40% more likely to die of any cause than a woman with a BMI over 25 but with a normal Waist to Hip Ratio.

The risk of death from cardiovascular disease, specifically, was similarly surprising for both men and women: a man of normal BMI but high WHR was 78% more likely to die of heart disease than a man with BMI and WHR in the normal range. A woman of normal BMI and high WHR was over twice as likely to die of heart disease than a woman of normal BMI and WHR.

What this means for you

Don't take this to mean that Body Mass Index is worthless. There is still a wealth of data linking greater BMI with increased risk of heart disease, diabetes, and cancer, among other diseases. What this does mean is that both Body Mass Index and Waist to Hip Ratio should be considered together in light of the greater risk to those with a higher Waist to Hip Ratio but normal Body Mass Index. If you feel you need to work on your waist, and not necessarily your weight, a Mediterranean style diet has been shown to help reduce that centrally-deposited fat.

First posted: December 2, 2015