Motivation and keeping a journal of what you eat are key components for shedding excess weight, according to new research.

Scientists at the University of Kentucky and the University of North Carolina at Chapel Hill found that the type of motivation for dieting and techniques to boost it when it dips could mean the difference between success and failure.

"Motivation has an impact on weight loss but the impact is really mediated by adherence to self-monitoring," said Kelly H. Webber, an assistant professor at the University of Kentucky. "If you are going to self-monitor your diet and exercise every day you are going to lose more weight.

Webber, who along with her colleagues reported the findings in the Journal of Nutrition Education and Behavior, said the best way to self-monitor is to keep a journal of everything you eat and how much you exercise.

The researchers studied two types of motivation, autonomous and controlled, during a 16-week weight-loss program involving 66 overweight women. Autonomous motivation is driven by personal reasons, while controlled motivation is based more on pressure from others and feelings of guilt.

They found that dieters who were self motivated and who kept a journal tended to be more successful.

"People who actually write down everything they eat and drink during the weight loss program are going to do better. And that is probably why commercial programs like Weight Watchers are very successful," said Webber.

All of the dieters were given questionnaires and asked to describe their motivation. Their weight loss and motivation were measured every four weeks during the program. They also measured their own progress with an online self-monitoring program.

"The importance of motivation is that it gets you to self motivate, which is the behavior that matters in weight loss," Webber explained.

Sustaining motivation was also essential because once it began to drop, usually between weeks four to eight, successful dieters who dropped 5 percent of their body weight were those who managed to keep the motivation going.

Webber suggested that if motivation starts to fall after about four weeks it would be a good time to boost it with initiatives.

"We think that contact with a counsellor is always helpful with motivation and contact with other people trying to lose weight," she said.

"Seek support. I think we need support to keep continually motivated. Some people are successful on their own but most of us need support."