Men who are overweight or obese face a much higher risk of premature death than overweight or obese women, researchers say.

The risk of premature death among overweight or obese people is three times as great in men as in women, a new study has found.

A global study of 3.9 million adults published in journal The Lancet has found being overweight or obese is associated with an increased risk of premature death.

The risks of coronary heart disease, stroke, respiratory disease and cancer are all increased.

Overall, the risk of death before the age of 70 is greatest among men.

WHO estimates that 1.3 billion adults worldwide are overweight, and that a further 600 million are obese.

In Australia, approximately 60 per cent of the population is overweight or obese based on the body-mass index (BMI), which relates weight to height.

According to the new study at the University of Cambridge in the UK, on average overweight people lose about one year of life expectancy, and moderately obese people lose about three years of life expectancy.

Dr Emanuele Di Angelantonio, lead author, says they also found that men who were obese were at much higher risk of premature death than obese women. This is consistent with previous observations that obese men have greater insulin resistance, liver fat levels, and diabetes risk than women.

Where the risk of death before age 70 would be 19 per cent and 11 per cent for men and women with a normal BMI respectively, the study found that the risk would be 29.5 per cent and 14.6 per cent for moderately obese men and women.

This corresponds to an absolute increase of 10.5 per cent for men, and 3.6 per cent for women - or three times as great.

The authors say that assuming that the associations between high BMI and mortality are largely causal, and those who were overweight or obese lost enough weight to bring them into the normal levels of BMI, then the proportion of premature deaths decreases to about one in seven people.