Those with a body mass index (BMI) of 21-25 were associated with the lowest risk of dying from cancer and heart disease, according to a peer-reviewed analysis of 3.6 million people and nearly 370,000 deaths.
The London School of Hygiene and Tropical Medicine, BMI – a measure of body fat – has long been a key indicator of health BMI could increase susceptibility to a shorter life expectancy.
Lead author, associate professor Krishnan Bhaskaran, said: "We know that BMI is linked to the risk of dying overall, but surprisingly little research has been conducted on the left to deaths from specific causes.
As well as cancer and respiratory disease and liver disease.
"We found important associations between BMI and most causes of death, highlighting body weight relative to height.
"BMI in the range 21-25 is linked to the lowest risk of dying from most diseases."
The report found BMI was linked to death from every major cause except transport-related incidents.
The causes included cancer, cardiovascular disease, neurological issues and self-harm.
The highest risk of cardiovascular death in those with a BMI of 25. Every 5-unit increase in BMI above this is associated with a 29 per cent higher risk, said the report, published in The Lancet Diabetes and Endocrinology Journal.
BMI of 21 – with every 5-unit increase associated with a 13 per cent higher risk.
BMI of at least 30 years. BMI of at least 30 years.
The report said the age of death for a 40-year-old healthy weight who had never smoked was 82.2 years for men, and 84.3 for women.
Obesity was associated with knocking 4.2 years ago that figure in men, and 3.5 years in women.
Class three obesity – those with a BMI of at least 40 – who associated with shortening life expectancy by 9.1 years in men and 7.7 years in women.
BMI calculators use factors such as age, weight and height to determine whether a person is of a healthy weight.
Responding to the study, Dr Michelle McCully, head of research evidence and interpretation at the World Cancer Research Fund, said: "Our research shows that overweight and obesity increases the risk of developing 12 cancers evidence that body weight affects both risk and survival from cancer.
"WCRF calls for action in creating health-enabling environments that support people in following our cancer prevention recommendations, of which one is maintaining a healthy weight."
In April this year, experts on the BBC's The Truth About Obesity revealed a way of telling if you're storing too much fat in your middle, using a piece of string.
Dr Margaret Ashwell said start by cutting a piece of string to the length of your height.
The next step, is to fold the piece of string in half and wrap it around your middle.
If the two ends of the struggle to meet, your visceral fat level is too high.