When considering the impact on life expectancy and long-term health the data tells us that obesity and smoking are in the same ballpark. Here is a recent research publication that puts some numbers to the very real costs of being overweight. The results are similar to those produced in past studies:
Researchers used data from the National Health and Nutrition Examination Survey (from years 2003 to 2010) to develop a model that estimates the annual risk of diabetes and cardiovascular disease in adults with different body weights. This data from almost 4,000 individuals was also used to analyze the contribution of excess body weight to years of life lost and healthy years of life lost.
Their findings estimated that 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). When one considers that these individuals may also develop diabetes or cardiovascular disease earlier in life, this excess weight can rob them of nearly two decades of healthy life. 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. "The pattern is clear - the more an individual weighs and the younger their age, the greater the effect on their health. In terms of life-expectancy, we feel being overweight is as bad as cigarette smoking."