Council scientists say that's why preventing weight gain after dieting is so difficult, The Copenhagen Post reported Monday. And the scientists say that proves more than 90 percent of dieters are back to their original weight two years after having stopped dieting.

Professor Bjorn Richelsen explained: "Weight loss has always been a threat to humanity. You cannot say the same about weight gain. This is where we find the explanation for why the body has mechanisms for regaining the weight."

And Richelsen says it doesn't make a difference what diet is used, the body's metabolism and muscles start working effectively together to regain the fat. Richelsen believes that reaction is due to the body's ancient defense-mechanism against hunger.

He advises people to keep an eye on their weight, and if there is a slight increase then respond immediately. "Those kinds of weight increases are manageable," he said.