In our culture, we value a lean body like the way Daniel Craig’s James Bond looks in a swimming trunk (see featured photo). But the reality is that most of us – men and women – do not have a lean and muscled body. On the contrary, according to the US Government, nearly seven out of 10 Americans weigh too much – 74% of men and 65% of women have been categorized as either overweight or obese. This is not just an American phenomenon; we read regular media reports that obesity has become a global problem with dire consequences on health and mortality.
But a new meta-analysis of the relationship between weight and mortality risk, involving nearly three million subjects and more than 270,000 deaths from more than a dozen countries, illustrates just how exaggerated and unscientific that claim is. The meta-analysis, published last week in the American Medical Journal, reviewed data from 97 studies to determine the correlation between body mass index and mortality risk.
The study, led by Katherine Flegal, Senior Scientist at the US National Center for Health Statistics, Centers for Disease Control and Prevention, found that all adults categorized as overweight and most of those categorized as obese have a lower mortality risk than the so-called normal weight individuals. In statistical terms, the study found a 6% decrease in mortality risk among people classified as overweight and a 5% decrease in people classified as grade 1 obese (most of the obese fall into this category). Watch the video below to hear what Dr. Flegal has to say about this study.
The measurement used by the World Health Organization and governments all over the world to measure obesity is the body mass index (BMI). The index is calculated by dividing weight in kilogram by height in meters squared. The widely used table for the BMI Index is as follows:
- Underweight – BMI of 18.5 or less
- Normal (healthy) weight – BMI of 18.5 to 25
- Overweight – from 25 to 30
- Obese Class I – from 30 to 35
- Obese Class II – from 35 to40
- Obese Class III – over 40
Thus a man six feet tall and 180 pounds would have a BMI of 24.4, considered normal; at 200 pounds his BMI would be 27.1, slightly overweight; at 230 pounds, his BMI of 30 would be considered obese.
Reactions to the results of the study
The results of the study stun those who assume that the definition of “normal” and “healthy” weight used by public health authorities is actually supported by medical literature. The study shows that this has not been the case. In fact over the years, much skepticism has been expressed about the scientific basis of BMI. Looking deeper into the matter, I learn that the BMI formula was devised by the Belgian mathematician Adolphe Queletet about 150 years ago. It was revived in 1970s and became an accepted standard measurement in 1990s.
The formula has many limitations. For example, it does not account for body frame size. A person may have a small frame, carry more fat than optimal but the BMI reflects that she is of normal weight. Conversely, a person with a large frame can be shown to be “overweight” even though the weight is optimal for the frame size. It does not take account of loss of height due to ageing. In this situation, BMI will increase without any corresponding increase in weight. BMI is particularly inaccurate for people who are fit and athletic, as the higher muscle mass tends to put them in the overweight category. Thus two persons of the same height and weight showing the same BMI can look very different as shown in the picture.
We need better measurements
What the study has proved is that BMI is a convenient but inaccurate measurement of weight, and it is not a good measure for the risk of heart attack, stroke or death. It is time that the authorities look into developing a better measurement than the one designed more than one-and-a-half century ago. This has real implications for healthcare – both public and private. Many private health insurance will use a particular BMI as a cut-off point; individuals with BMI over the cut-off point have to pay a higher premium to reflect the higher “risk”, or may even be denied insurance cover altogether. This situation should not be allowed to continue.