Obesity, Waist-to-Hip Ratio and Mortality

Some studies, and in particular a very recent one (reference 5), claim that BMI is a very poor predictor of obesity-related illness, and in particular, future heart attacks. They studied 27,000 participants from 52 countries around the world, at their first myocardial infarction ("heart attack"). In addition to determining BMI, they measured the body circumference at the hip and waist. 15,000 patients were compared to a similar number of people ("control group") who had no history of coronary disease, and were matched by age and sex. They find that the dependence of coronary risk on BMI is due mainly to its dependence on the waist-to-hip ratio ("WHR"). The WHR turns out to be a more accurate predictor of coronary risk - The group of people with the highest WHR has 2.5 times the risk compared to the group with the lowest WHR. The margin of error was 2.3 to 2.7.

Being obese leads to an increase in related risk factors, such as diabetes and hypertension. When these risks ("confounding factors") are subtracted (i.e, an obese person, who is not diabetic, hypertensive, etc.) they still find an increased risk of 1.75, for the highest vs. the lowest WHR.

The article leaves out some details that would be of considerable interest. For example, it does not specify the values of WHR for each risk group. However, it clearly demonstrates that having a "protruding middle" is associated with a significant increase in the risk of heart attacks.

The three most recent studies (and meta-studies) are presented in references 6-8. While the study in reference 6 (involving 60,000 people with a 10 year followup) states that both overweight and obesity among men and women increase the risk of death, actual consideration of their results leads us to conclude that only being obese increases the risk to a statistically significant level.

A study of 1,200,000 (!) Koreans, tracked for 12 years (reference 7), shows similar results. While there seems to be a trend towards increased risk for overweigt people, the risk really becomes statistically significant for a BMI above 30.

Reference 8, a meta-study in "The Lancet", even goes further: they determine that the combination of 40 studies, totalling 250,000 patients, followed for 3-8 years leads them to conclude that people with a BMI between 25 and 30 ("overweight" but not "obese") actually have a lower risk of death: 0.87 (13% lower risk, Margin of Error between 0.81 to 0.94), compared to people with the "ideal" BMI of 24!

Clearly we can conclude that being overweight is not associated with any significant mortality hazard!

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Last Modification - September 3, 2006