Wednesday 13 May 2009
The idea that ‘fatness equals an early death’, promoted by the public-health community and the weight-loss industry, continues to dominate popular discussion of obesity and the thinking of regulators. This is despite the publication four years ago of two studies decisively refuting the claim that having the ‘wrong’ body mass index (BMI) increases one’s risk of premature death. But despite what the scientific evidence about fat, disease and death actually says, the scaremongering continues.
The two unimpeachable studies were by Katherine Flegal and her colleagues from the US Centers for Disease Control and Prevention (CDC) and Jerome Gronniger of the Congressional Budget Office. Counter-intuitively, perhaps, Flegal et al found that overweight Americans were those most likely to live the longest. In the US population, Flegal found, there were more premature deaths among those with BMIs of less than 25 – the so-called normal weight – than those with BMIs in excess of 25. In fact, the lowest death rates were in the ‘overweight’ category of BMIs from 25-29.9.
In his study, Gronniger looked at weight and mortality for each BMI point rather than through simply comparing, as is usually done, mortality across broad categories such as underweight, normal, overweight, and obese. Gronniger found, for example, that: ‘Men in the “normal” weight category exhibited a mortality rate as high as that of men in the moderately obese category (BMIs of 30-35), and men in the ‘overweight’ category clearly had the lowest mortality risk…Normal-weight individuals of both genders did not appear to be relatively more long-lived than mildly obese individuals… whereas overweight people (BMIs of 25-30) appeared healthiest of all.’
Noting that his study and others ‘suggest that individuals who are overweight and mildly obese face no, or very little, increased mortality risk relative to normal-weight individuals’, Gronniger cautions that ‘it seems best to avoid exaggerating the mortality risks faced by individuals with BMIs below 35’.
Finding other ways to measure fatness
None of this was welcome news to those who are in the business, literally, of convincing the underinformed public and misinformed governments that we are in the midst of an unprecedented and catastrophic obesity epidemic that will take the lives of millions. Since the BMI data fails to provide the requisite number of fat corpses, some other sort of link between being overweight and obese and an early demise must be established.
Several alternatives to the BMI have been suggested, including such anthropometric variables as body shape, waist-to-hip ratio, skinfold thickness, and waist circumference. Some studies using these alternative measures have already concluded that these new yardsticks can distinguish those at risk of weight-related ill-health.
But is this really the case? Or do these new measures of supposedly ‘unhealthy’ weight also fail to demonstrate a risk?
The answer to these questions is found in a new study from the CDC’s Katherine Flegal and Barry Graubard. They used the Third National Health and Nutrition Examination Survey (NHANES III), which provided data on a variety of alternative measures of overweight and obesity, such as percentage of body fat, skinfold thickness, waist circumference, and waist-hip ratio, for a representative sample of the US population.
For each of these alternative measures, the authors looked at three population groups: low BMI (less than 18.5), intermediate (BMI of 25-30), and high (BMI above 30). This data was then linked with death certificate data to determine the number of excess deaths associated with the three different levels of each of the alternative obesity measures. For instance, Flegal and Graubard were able to calculate how many extra deaths were linked to having a low, intermediate, and high percentage of body fat, a high waist-to-hip ratio, an abnormal skin fold thickness, and so on.
The results are striking. For the intermediate level of each of the alternative measures of obesity, there was a negative link with mortality. In other words, those with a higher waist circumference, or a higher percentage of body fat, or waist-to-hip ratio, had lower mortality. And for those with high measurements, there were no statistically significant associations with increased morality risks.
The results from these new and supposedly more accurate measures of overweight and obesity are the same as from BMI in that they show no significant risks of mortality for those at the higher levels. Equally importantly, they show that those at the intermediate range – by current definitions, the overweight – actually live longer, just as the BMI data suggests.
Not dying, just unhealthy?
Of course, it might still be argued that while there was no association between these sorts of measures of overweight, obesity and overall mortality, there might still be a link between these measures, certain diseases, and premature death. For example, the World Cancer Research Fund has (yet again) asserted this week that there is a link between obesity and cancer deaths. (For more on the WCRF claims, see Four flabby myths about obesity and cancer, by Patrick Basham and John Luik.)
In order to assess this possibility, Flegal and Graubard looked at 21 diseases that are commonly linked to obesity, including cardiovascular disease, diabetes, and various cancers, such as colon cancer, esophageal cancer, and breast cancer. They examined the link between each disease, death rates, and the level of each alternative obesity measure.
Once again, there were no statistically significant associations between the intermediate and high level of any measure and death from any of the ‘obesity-related’ diseases. As Flegal and Graubard write: ‘the associations of the corresponding levels of other anthropometric variables – including waist, hip and arm circumferences; percentage body fat…waist-hip ratio; the sum of four skinfold thicknesses, and the waist-stature ratio - also tended to be weak and in general were quite similar to the association of BMI with mortality…These findings do not suggest that the weak adiposity-mortality associations would be stronger if measures of adiposity other than BMI were used.’
In other words, there are no statistically significant associations between being fat and premature death or death from obesity-related diseases, regardless of which measure of overweight and obese is used. In fact, as with BMI, those who had higher-than-normal readings of these alternative obesity measures had a lower risk of dying early.
Previously on spiked Patrick Basham and John Luik exploded four fat myths about cancer and obesity. They reviewed a year of myths about smoking and obesity. They also examined new research which taught obesity hysterics a lesson and attacked the proposals to remove children from obese households. Dr Michael Fitzpatrick said we should stop bullying fat kids. Rob Lyons was sick of the endless diet of government intervention. Or read more at spiked issue Obesity.
‘Excess deaths associated with underweight, overweight and obesity’, by KM Flegal et al, Journal of the American Medical Association 293 (2005): 1861-1867
‘A semi parametric analysis of the body mass index’s relationship to mortality’, by JT Gronniger, American Journal of Public Health 96 (2005): 173-178
reprinted from: http://www.spiked-online.com/site/article/6659/