It seems intuitive (at least in American culture) that obesity isn't healthy, but no observation is too obvious to be worth confirming scientifically. And a study by epidemiologists at the McGill University Health Centre provides new evidence that obesity can shorten a person's life by years — eight, to be exact (or even more, depending on how you count obesity's effects).
In a collaborative effort including researchers from several Canadian universities, the epidemiologists developed a computer model to make sense of data on almost 4,000 Americans collected between 2003 and 2010. The data came from the National Health and Nutrition Examination Survey, an important source because it reflects information from both interviews and physical examinations (whereas merely self-reported data on weight would be much less reliable).
Their findings basically corroborate conventional thinking on excessive weight and its ill effects on health:
Individuals who were very obese could lose up to 8 years of life, obese individuals could lose up to 6 years, and those who were overweight could lose up to three years. In addition, healthy life-years lost were two to four times higher for overweight and obese individuals compared to those who had a healthy weight, defined as 18.5-25 body mass index (BMI). The age at which the excess weight accumulated was an important factor and the worst outcomes were in those who gained their weight at earlier ages.