Being moderately overweight could actually be good for you, say researchers.
Obesity puts people at risk of many diseases, warn experts
People who are a little overweight are likely to live longer than people who are underweight or obese, a study shows.
But experts pointed out that the study only looked at how long people lived and not at obesity-related diseases.
The American Centres for Disease Control research appears in the Journal of the American Medical Association.
The US team looked at data from three US surveys about health and nutrition carried out in the 70s, 80s and 90s.
Weight was assessed using a measurement called Body Mass Index - calculated by divide a person's weight in kilograms by the square of their height in metres.
A BMI of 18.5 to 25 is considered normal. One below 18.5 is considered underweight and 30 or above is considered obese.
The researchers found that the people who had BMIs higher than 25 but lower than 30, which meant they were moderately overweight but not obese, did not have a reduced life expectancy.
The people who lived the longest of all were those with BMIs of 25, which lies between the ideal and overweight margins.
In comparison, there were 112,000 extra deaths among the obese category and nearly 34,000 extra deaths among the underweight category.
When the researchers compared the trends over the three decades studied, they found the death risk linked with obesity had decreased over time.
They said this might be down to people being healthier and getting medical treatment for obesity-related conditions such as heart disease.
US researchers recently estimated that, based on the current obesity levels, life spans could fall by between four months and nine months.
If the rise in obesity - 50% a decade in both the 1980s and 1990s in the US - was not stopped, the team said it could fall by two to five years within decades.
Dr William Cochran, a nutritionist for Pennsylvania's Geisinger Health System in the US, said the new research could cause confusion about whether being overweight is unhealthy.
"I think like most things, it's a mixed bag and the truth is not always black and white.
"But there is positively, absolutely, undeniably no doubt that being obese is not good for you."
In the UK it is estimated that one in five men and a quarter of women are obese.
Dr David Haslam, chair of the National Obesity Forum, said: "These findings should certainly set us thinking.
"Even though we are getting fatter, in a society that is putting more emphasis on a healthier lifestyle, the impact may be lessened.
"In this study the risk of death from heart disease does not appear to be as high as a generation ago, however, the risk of developing diabetes has not decreased.
"This shows that while medical management of diseases associated with obesity have improved the need for concerted public health campaigns and best practice in treatment of obesity must be paramount."