If you want to keep trim, forget the diet books and gym membership - you may be better off just brushing your teeth more often, according to a Japanese study.

In a survey of the everyday habits of nearly 14,000 people whose average age was in their mid-40s, Dr. Takashi Wada of Jikei University in Tokyo found that those who managed to stay slim tended to brush their teeth after every meal.

Overweight men sometimes went more than a day without brushing their teeth, according to the study, published in the Journal of the Japan Society for the Study of Obesity.

Wada and his team compared the lifestyles of people whose body mass index (BMI) was over 25 - the level doctors define as overweight - with those of slimmer people. The survey covered eating and drinking habits, sleep, work and exercise.

The results do not mean that brushing in itself constitutes a fat-burning exercise, the authors say.

“It’s a sign that these people are careful about their health - they want to maintain the appearance of their teeth and prevent bad breath,” the paper said. “We think actively encouraging the habit of toothbrushing would play a role in maintaining health and would help prevent Obesity.”