LONDON (Reuters) - People who eat quickly until full are three times more likely to be overweight, a problem exacerbated by the availability of fast food and the decline of orderly dining habits, Japanese researchers said on Wednesday.

The findings, published in the British Medical Journal, highlight how eating styles, and not just what or how much is eaten, can contribute to an obesity epidemic fueled by the spread of Western-style affluence in many parts of the world.

The World Health Organization classifies around 400 million people as obese, 20 million of them under the age of five. The condition raises the risk of diseases like type 2 diabetes and heart problems.

For their study, Hiroyasu Iso and colleagues at Osaka University asked more 3,000 Japanese volunteers aged 30 to 69 about their eating. About half of the men and a little more than half of the women said they ate until full. About 45 percent of the men and 36 percent of the women said they ate quickly.

Those who said they ate until full and ate quickly were three times more likely to be fat than people in the "not eating until full and not eating quickly" group, the researchers found.

They cited as causes both the availability of cheap food in big portions and habits like watching television while eating.

To counteract the "supra-additive effect" of speedy or glut eating among children prone to obesity, parents should encourage them to eat slowly and in calm surroundings, the study found.