Being severely obese can knock up to eight years off your life and cause decades of ill health, a report says.
The analysis showed being obese at a young age was more damaging to health and life expectancy. The team, at McGill University in Canada, said heart problems and type 2 diabetes were major sources of disability and death.
Experts said people were frequently "ignorant" of the consequences of obesity. The health problems caused by obesity are well known.
The report, in the Lancet Diabetes and Endocrinology, used a computer model to take those risks and calculate the impact of weight on life expectancy throughout life.
In comparison with 20 to 39-year-olds with a healthy weight, severely obese men of the same age lost 8.4 years of life and women lost 6.1.
Men also spent 18.8 more years living in poor health while women spent 19.1 in that state.
Moving up an age group to those in the forties and fifties, men lost 3.7 years and women 5.3 years to obesity.
Men and women in their sixties and seventies lost just one year of life to obesity, but still faced seven years in ill health.