BAKERSFIELD, Calif. -- Earlier research has shown that shedding pounds tends to put people in a good mood, no matter what diet they are on, but little research has been done on the long-term effects a diet can have on a person's mood.

Researchers in Australia compared the moods of dieters on the traditional low-fat, low-calorie diet to those on a low-carb diet over the course of a year of dieting.

They found that weight loss was the same for both groups and both experienced a boost in positive mood during the first few weeks of dieting, but the good mood was short-lived for those on the low-carb diet.

While those on the low-fat diet sustained their elevated mood throughout the year, moods began to decline for low-carbers after the first 8 weeks.

Researchers speculated that this may be because low-carb diets have less flexibility than low-fat diets and they tend to be socially difficult to keep up.

Also, carbohydrates have been linked with the production of positive mood chemicals in the brain, so researchers said it's possible that the lack of carbohydrates themselves affected dieter's mood.