Obesity shaves two to four years off the average lifespan , while being very obese can shorten your lifespan by 8 to 10 years , according to a new analysis of 57 studies including nearly 900,000 people . Men and women with BMIs between 22.5 and 25 were the least likely to die during the study 's follow-up period . `` This is scary and something that we should pay close attention to , '' says Ali Mokdad , Ph.D. , a professor of global health at the Institute for Health Metrics and Evaluation at the University of Washington in Seattle . The new findings actually underestimate the true impact of obesity on society because they do n't address the costs of obesity-related illness and other factors , says Mokdad , who was not involved with the current study . The study , published online March 18 in the journal The Lancet , was conducted in part by the eminent epidemiologist Sir Richard Peto of the University of Oxford . Peto and his colleagues in the Prospective Studies Collaboration , a team of dozens of researchers from around the world , say they did the new study to figure out exactly how body mass index ( BMI ) relates to mortality . Researchers also investigated how smoking influenced this relationship and how excess weight affected death risk from specific causes . Their analysis included 894,576 people , mostly from North America and Western Europe . Most were age 46 when the study started and were recruited in 1979 ; the average BMI for all participants was 25 . The researchers eliminated deaths during the first five years of their analysis to avoid including people who were excessively thin because of illness . A BMI of 18.5 to 24.9 is normal ( that translates to weighing between 114 and 149 pounds if you 're 5 feet 5 inches tall ) ; overweight is 25 to 29.9 ( 150 to 179 pounds if you 're 5 feet 5 inches tall ) ; and obese is 30 or more ( 180 pounds-plus on a 5-foot-5-inch frame . ) You can figure out your BMI at the National Institutes of Health Web site . Men and women in the new analysis who had BMIs between 22.5 and 25 were the least likely to die during the follow-up period , which averaged eight years . But every additional 5 BMI points boosted mortality risk by 30 percent . The increase was strongest for deaths due to cardiovascular disease , diabetes , kidney , and liver disease ; cancer deaths also went up with increasing BMI , but not as much as other diseases . Health.com : How to find your healthiest body mass index . People with BMIs below 22.5 had a higher mortality risk during the study than those who weighed slightly more , largely because of respiratory illnesses , such as lung cancer . The researchers say this is probably the result of skinny people who were smokers . The researchers calculate that having a BMI of 30 to 35 takes to two to four years off the average lifespan compared with having a BMI of 22.5 to 25 . Having a BMI between 40 and 45 ( for example , being 5 feet 5 ' and weighing 240 to 270 pounds ) , they say , reduces one 's lifespan by eight to 10 years . This reduction in lifespan is on par with being a heavy smoker . Health.com : Dietary fats can help -- or harm -- your heart . This is n't too far out of line with research conducted by Katherine M. Flegal , Ph.D. , a senior research scientist and distinguished consultant with the Centers for Disease Control and Prevention 's National Center for Health Statistics . In a 2005 study , Flegal and her team reported that while being obese ( having a BMI of 30 or above ) shortened lifespan , those who were overweight ( a BMI of 25 to 29.9 ) were at no greater risk of death , and may actually have had a lower mortality rate in a given time period than their normal-weight peers . Health.com : How to cut up to 900 calories with simple substitutions . While the study kicked up a lot of controversy -- some people thought the findings minimized the health effects of excess weight -- several other studies have also found no greater mortality risk associated with being overweight ( but not obese ) , and possibly lower mortality , Flegal notes . Given the difficulty of losing weight , the authors of the new study say , it may be best if people are motivated to prevent the weight gain in the first place . For example , a person who held their BMI steady at 28 rather than going up to 32 ( typical of the increase seen in middle age ) could extend their life by two years , the researchers say , while a young adult who maintained a BMI of 24 rather than going up to 32 could add three years to his lifespan . Health.com : BMI success story : How one woman lost 44 pounds . For this to happen here , Mokdad notes , the United States government is going to have to do a much better job of supporting prevention efforts . A `` bailout '' for such efforts that translated to healthier American and workers could be a pretty effective economic stimulus , he added . Try a FREE TRIAL issue of Health - CLICK HERE ! Copyright Health Magazine 2009 .
Study : Obesity shortens life by 2-4 years ; the very obese could lose up to 10 years . Higher mortality because of diabetes , cardiovascular , kidney and liver disease . Cancer deaths also went up with increasing BMI , but not as much as other diseases . Another study had found that being overweight , but not obese , did n't shorten life .