Are you sure you want to lose weight?

The relative risk of having a Body Mass Index in different ranges. Being overweight or being obese (Class I) results in a lower risk of death than being 'normal'.

The relative risk of having a Body Mass Index in different ranges. Being overweight or being obese (Class I) results in a lower risk of death than being ‘normal’. The error bars represent a 95% confidence interval.

Welcome to 2013! It may be that you – like me – are considering losing a little weight. But if you are considering a diet or exercise regime, then you should be aware that a new study confirms that although you may feel better, you will also be increasing your risk of an early death.

I have written about this before (here), but this new study by Flegal et al (available free here) confirms this result a fortiori . The work is a ‘meta’ study covering more than 2.8 million people on several continents – mainly Europe and the US – and has recorded more than 270, 000 deaths. Thus the relative risks of being overweight can be isolated from many other causes. The results (see the Figure above) confirm that being ‘overweight’ reduces the relative risk of death (the Hazard Ratio) compared with being ‘normal’. They even confirm that being Class I obese still offers a protective effect. Higher levels of obesity increase the risk the of death significantly.

This result is important in a social context where right-wing think tanks suggest that the benefits of overweight unemployed people should be cut if they fail to exercise (Guardian, BBC). Their aim – no doubt laudable – is to reduce the burden of obesity-related disease on the National Health Service. However the data here indicate that the consequence would be to increase the risk that these people would die. This is not a morally defendable position. Indeed, this work seems to me to call into question every piece of government advice on the topic of obesity.

The Journal of the American Medical Association has an accompanying editorial discussing the work:

“The optimal BMI linked with lowest mortality in patients with chronic disease may be within the overweight and obesity range. Even in the absence of chronic disease, small excess amounts of adipose tissue may provide needed energy reserves during acute catabolic illnesses, have beneficial mechanical effects with some types of traumatic injuries, and convey other salutary effects that need to be investigated in light of the studies by Flegal et al and others.”

Not all patients classified as being overweight or having grade 1 obesity, particularly those with chronic diseases, can be assumed to require weight loss treatment. Establishing BMI is only the first step toward a more comprehensive risk evaluation.

In other words being marginally overweight is a good thing if you fall ill – because you can draw on the energy in the fat if you are not eating. However its also states that there are “other salutary effects that need to be investigated in light of the studies by Flegal et al and others.” In other words “We don’t understand this, but its real”.

My body mass index is around 27 kg/m2, close to the UK average so I am technically overweight. I also feel overweight. And I understand that this increases my risk of disease (morbidity). However, it also reduces the risk that I will die from it (mortality). Nothing in life is as simple as we would like it to be!

Happy New Year.

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