4 in 10 US women now classed as obese

Rates of obesity between men and women have been largely comparable in recent years, but females have now surged ahead to around 40 per cent, compared to 35 per cent of males.

The figures, which were obtained by the Centers for Disease Control and Prevention and were published in two articles published by the Journal of the American Medical Association, are largely based on a small government survey considered the best measure of the country's obesity problem.

Dana Hunnes, a dietician who sees obese patients at Ronald Reagan UCLA Medical Center in Los Angeles, said the figures should come as a warning to the whole nation.

"It's a really alarming figure, and it's alarming that it's continuing to go up despite government calls to action on weight loss and healthy eating," she said.

Ms Hunnes added that the reason for men not seeing the same rising levels of obesity was currently unclear, although the World Health Organisation insists women are more likely to be seriously overweight than men.

Side effects from obesity include diabetes, heart disease and other serious health problems, although experts insist the growth of the problem has stalled.

Nevertheless, the new figures suggest the problem is not improving, with black women (57 per cent) found to be the most affected when the figures were broken down, ahead of Hispanics (47 per cent),  whites (38 per cent) and Asians (12 per cent).

The problem is not increasing as dramatically as it was, but the new numbers show it is clearly not improving, said Dr. Felipe Lobelo, an Emory University researcher who focuses on obesity and physical activity.