According to the research, severe obesity shortens life by a decade and even moderate obesity will shorten life by about three years. The findings are published in The Lancet and are the results of research on almost a million people around the world.
Researchers used body mass index (BMI) as a measure of obesity. BMI is useful for assessing the extent to which fatty tissue causes ill health.
It is calculated by dividing a person's weight in kilograms by the square of their height in metres. A person 1.70m tall would be considered moderately obese if they weighed 90kg rather than the ideal 70kg.
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Each incremental rise in BMI above the healthy zone of 20-25 increased premature death risk, the Clinical Trial Service Unit concluded. Severe obesity - a BMI of 40 to 50, which applies to about 2% of the UK population - reduced life expectancy by about 10 years.
Moderate obesity - a BMI of 30-39, which applies to one in four UK adults - reduced life expectancy by three years. Much of the obesity-related risk is down to heart disease and stroke, and to a lesser extent cancer.
Amongst middle-aged people in the UK, as many as one in four deaths from heart attack or stroke and one in 16 cancer deaths are due to being overweight or obese, the researchers estimate.
