Obese most likely to die early but those classed as overweight have better survival rate.

Overweight people have surprisingly beaten out your normal Joe Average on the mortality scale, a statistical survey of medical studies has shown - despite a well-established link between weight and sickness.

When talking of health, "death is a rather crude tool", said Auckland District Health Board clinical director Robyn Toomath, who is sceptical of the paper.

The survey, published in the Journal of the American Medical Association, collated 93 studies tracking population groups over several years.

It compared how often participants died based on BMI - or body-mass index, a ratio between height and weight - using World Health Organisation categories that predict Type 2 diabetes.


People in the "overweight" BMI category were found to have a death rate 6 per cent less frequent than those whose BMI was "normal".

The "obese", however, were 18 per cent more likely to have died.

The authors of the paper suggest that overweight people might be more likely to seek and receive medical help.

Dr Toomath said the findings had little relation to public health. Diseases had already been shown to be more likely in overweight people - but "disease isn't necessarily the same as death".

The study also mixed the death rates of people of different ages. For people older than 75, body weight could be a positive sign of being well nourished, Dr Toomath said.

The best way to reduce public health costs for the country was still to help people eat healthy and stay slim, by restricting the marketing and value of junk foods or promoting nutritious foods, she said.

Dr Steven Hymsfield, of the Pennington Biomedical Research Centre in Louisiana, told National Public Radio in the US of some chance scenarios where fat could help you live.

"If you fall and you fall on vulnerable bone, like the hip, having a little extra fat there might protect you from hip fracture," Dr Hymsfield said.

Or if an illness left you unable to eat, extra body fat could be useful, he said.

Helen Walls, a research fellow at Australian National University, wrote in the Herald yesterday that the biggest mortality risks were associated with the heaviest fifth of the population, rather than those in the overweight bracket.

Roughly a third of New Zealanders fit each of the categories of normal, overweight and obese.

About 1 per cent are considered underweight.

On the scales:
34 per cent of NZ adults
=BMI 18.5-25, for

160cm: 47-64kg

170cm: 53-72kg

180cm: 60-81kg

37 per cent of NZ adults
-6 per cent lower chance of death
=BMI 25-30, for

160cm: 64-77kg

170cm: 72-87kg

180cm: 81-97kg

28 per cent of NZ adults
+18 per cent higher chance of death
=BMI 30+, for

160cm: 77kg+

170cm: 87kg+

180cm: 97kg+

Source: Journal of the American Medical Association