The obesity paradox

The obesity paradox

By Margaret McCartney

Published: June 13 2009 02:01 | Last updated: June 13 2009 02:01

Jamie Oliver, chef-champion of the British waistline, is taking his healthy-eating campaign to the US. We’ll see the results next year, when the six-part series is due to be broadcast. Meanwhile, in the UK, public health adverts feature small girls eating fairy cakes under the slogan: “is a premature death so tempting?” Guilt is ladled on everywhere.

Obesity is discouraged by doctors, and in many ways, this is quite right. Research has linked obesity to serious conditions such as cardiac disease and diabetes; an obese person’s quality of life is also badly compromised. After carrying my smallest child for half an hour, I am reminded that an extra stone in weight slows you down, wears the joints and tires you out. Never mind the effects of obesity on self-esteem.

But in certain conditions, obesity has been found to have advantages. Some people have dubbed this the “obesity paradox”: patients who you might think would fare worse because of their corpulence actually do better than those of normal weight.

Researchers have tried to explore this subject by relating obesity to outcomes. Congestive cardiac failure, where the heart becomes unable to pump the normal amount of blood with the same power, was found to have a better prognosis if the patient was obese. At first, this was thought to be misleading. People often lose weight when they fall ill, so exact comparisons by body size are difficult. Could it also be possible that doctors presumed a worse outlook for obese people, and therefore intervened earlier and with more powerful treatments? In 2007, the American Heart Journal published a study of more than 100,000 patients with heart failure. It found that a high body mass index was associated with lower hospital mortality rates.

This could be a trick of the numbers – patients in the high BMI group were more likely to be younger, with better cardiac function – but there are other conditions where this same paradox is present. Kidney dialysis patients who are obese have better survival outcomes compared with those of normal weight. Why? Many theories have been put forward – from hormonal regulation to nutrition. But there are dangers in looking for too many potential associations: if you search hard enough, some associations will be positive simply by chance alone. One needs to be sure that the study is done with enough statistical power to be certain about the outcomes.

And should the research be done at all? Some people have been concerned that even raising the possibility that obesity may have advantages could do a disservice to public health. It would be an even greater pity, though, if research that could help define and explain these findings never got done.

Margaret McCartney is a GP in Glasgow
margaret.mccartney@ft.com

For lively discussion of the latest medical issues go to Margaret McCartney’s blog at blogs.ft.com/healthblog

http://www.ft.com/cms/s/2/add87aec-555a-11de-b5d4-00144feabdc0.html