'Weight is healthy' study criticised
A study which suggests being overweight can lead to a longer life has caused controversy among obesity experts.
One labelled the findings a "pile of rubbish" while another said it was a "horrific message" to put out.
The research, in the Journal of the American Medical Association, suggested the overweight were less likely to die prematurely than people with a "healthy" weight.
Being underweight or severely obese did cut life expectancy.
The researchers at the US National Centre for Health Statistics looked at 97 studies involving nearly 2.9 million people to compare death rates with Body Mass Index (BMI) - a way of measuring obesity using a person's weight and height.
A healthy BMI is considered to be above 18.5 and below 25. However, overweight people (with a BMI between 25 and 30) were 6% less likely to die early than those considered to have a healthy weight, the study reports.
Mildly obese people (BMI between 30 and 35) were no more likely to die prematurely than people with a healthy BMI.
The study said being "overweight was associated with significantly lower all-cause mortality".
Possible explanations included overweight people getting medical treatment, such as to control blood pressure, more quickly or the extra weight helping people survive being severely ill in hospital.
However, the researchers point out they looked only at deaths and not years spent free of ill-health.
On Tuesday, the Royal College of Physicians called for the UK to rethink the way it tackles obesity.
Prof John Wass, vice-president of the college, said: "Have you ever seen a 100-year-old human being who is overweight? The answer is you probably haven't."
He said the largest people will have died years before and pointed to health problems and higher levels of Type 2 diabetes.
"Huge pieces of evidence go against this, countless other studies point in the other direction."
Other experts criticised the research methods.
"Some portion of those thin people are actually sick, and sick people tend to die sooner," according to Donald Berry, from the University of Texas
Dr Walter Willett, from the Harvard School of Public Health said: "This is an even greater pile of rubbish" than a study conducted by the same group in 2005.
Tam Fry, from the National Obesity Forum in the UK, said: "It's a horrific message to put out at this particular time.
"We shouldn't take it for granted that we can cancel the gym, that we can eat ourselves to death with black forest gateaux."