Who's afraid of … being fat?
Author: John Luik
Article Published: 29 January 2008
The last few weeks have been a tough time for the fatties among us - which is supposedly most of us. According to the recent report from the American Institute for Cancer Research and the World Cancer Research Fund, being fat and eating certain foods increases our risk of cancer.
The secret to a long life, according to the report’s authors, is to be as thin as you can, while avoiding red meat, processed meats, alcohol, French fries, milk shakes and… well, you get the picture. Another report published the same week, based on the Million Women Study in the UK, suggested that 6,000 UK cancer deaths per year could be blamed on obesity. (For a critical view of these two reports, see "Contestable Conclusions" by Basham and Luik.)
In contrast to these reports, a careful new study about obesity by Katherine Flegal and colleagues from the Centers for Disease Control (CDC) and the National Cancer Institute could do much to calm our growing hysteria about obesity.
Flegal used data from the National Health and Nutrition Examination Survey, which is a representative sample of the US population, to find out what the connection was between body weight and a range of diseases, including cardiovascular disease (CVD), cancer and all other causes of death such as diabetes and kidney disease, chronic respiratory disease, infectious diseases, homicides etc. The results are startling since they confound much of the received wisdom about being fat in America.
For one thing, Flegal discovered that being ‘overweight’ - a body mass index (BMI) of 25-29.9 - was not associated with increased mortality. (To see how weight and height correspond to BMI, see this page.) In fact for CVD, cancer and all other causes, being overweight actually increased one’s chance of living longer. In total, overweight was associated with a total of 138,281 fewer deaths in the USA. Being overweight is not likely to kill you.
Second, Flegal found that being obese increased the risk of premature death but mostly only for those with a BMI over 35. For a typical man, a BMI of 35 means being overweight by roughly 30kg or 66 pounds. In other words, even modest obesity is not a death sentence. For example, those with BMIs of 30-35 aged 25-69 did not have a statistically significant increased risk of dying from cardiovascular disease.
The results for cancer are even more startling since even those with BMIs in excess of 35 did not have a statistically significant increased risk of dying. For cancers considered obesity-related there was no statistically significant association between excess deaths and overweight. And for all other diseases other than CVD and cancer, obesity up to a BMI of 35 was modestly protective - that is, being plump seems likely to result in a longer life. In short, even moderate obesity is not likely to kill you.
Third, being underweight carries substantial risks. Whereas obesity accounted for an annual total of 95,442 deaths in the USA, being thin was associated with 46,398 or almost half as many deaths as obesity. But then one is unlikely to ever hear about the risks of being thin or the mortality toll associated with underweight. Put slightly differently, in 2004 overweight was associated with reduced mortality for a gain of 138,281 lives, whereas obesity - mainly extreme obesity - claimed 95,422, meaning that between overweight and obesity there was no net loss of life. But there was a significant net loss of 46,398 lives associated with being too thin.
Nor are these findings a fluke. These latest results mirror those published by Flegal and the same team in 2005. In the 2005 study, the researchers found that being overweight reduced one’s chances of dying, that the majority of deaths due to obesity were in the morbidly obese, and perhaps most surprisingly, that there was no statistically significant increased risk for death associated with even modest obesity.
The implications of these findings are significant. They suggest that most Americans need not worry about being too fat, since most mortality is associated with BMIs in excess of 35. They suggest that the continual message from the government and the public health community to lose weight or to be as thin as possible lacks a credible scientific basis. And they suggest that those who weigh too little deserve some attention and sympathy.