Among the 500,000 US adults who were evaluated, those who were just slightly overweight in their 50s were 20-40 percent more likely to die in the next decade, researchers reported. Similar results were drawn from a Korean study of more than a million adults. Both studies are published in the New England Journal of Medicine.

The latest conclusions are likely to leave many Americans -- particularly Baby Boomer who are experiencing middle-aged weight gain en masse -- confused. Earlier research by the US Centers for Disease Control and Prevention and the National Cancer Institute concluded that being slightly overweight lowered the risk of death

Some critics are already dismissing the analysis as flawed and needlessly alarming.

One of the new studies is an analysis of 500,000 AARP members who self-reported their weight, which casts some doubt on the accuracy of the findings. Overall, the risk of death was higher for slightly overweight women but not for men who carried a few extra pounds.

However, when the researchers looked at the data on 186,000 healthy men and women who had never smoked, they found that being overweight raised the risk of death 20-40 percent for both men and women, compared to people within the normal weight range.

Obese people were two to three times more likely to die prematurely than normal-weight people.

What is indisputable is that Americans are steadily getting heftier, with about two-thirds of the adult population considered overweight and a third tagged as obese. Obesity has been linket to increased risk of heart disease, diabetes, cancer and arthritis.