The US health watchdog has reaffirmed that being overweight is unhealthy, dismissing a controversial report that suggested that adding a few extra kilos was no cause of concern.

"It is not OK to be overweight. People need to be fit, they need to have a healthy diet, they need to exercise. I'm very sorry for the confusion that these scientific discussions have had," Centres for Disease Control and Prevention (CDC) chief Julie Gerberding told a new conference in Atlanta Thursday

She said obesity and overweight had many adverse consequences including increased risk of heart disease, some cancers, and diabetes, reports Xinhua.

Gerberding acknowledged potential flaws in a recent controversial study by the CDC scientists that had suggested that being overweight may not be as life threatening as once thought.

The study, published in April, linked obesity with 25,814 deaths a year in the US, dramatically lower than the 365,000 deaths estimated some months earlier. It also said the risk of death was 20 percent lower for mildly overweight people in comparison with those who were slim.

Many scientists from the Harvard School of Public Health, the American Heart Association and the American Cancer Society had objected to the conclusions of the study.