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People who chew their food more take in fewer calories, mainly because more chewing is related to the levels of hormones that regulate appetite, according to a Chinese study.

Chewing food 40 times instead of a typical 15 times caused the study participants to eat nearly 12 per cent fewer calories, according to a study published in the American Journal of Clinical Nutrition .

"Compared with lean participants, obese participants had a higher ingestion rate and a lower number of chews per one gram of food," wrote lead researcher Jie Li and colleagues from Harbin Medical University in China.

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"Regardless of status, the subjects ingested 11.9 per cent less after 40 chews than after 15 chews."

Dr. Li's team gave a typical breakfast to 14 obese young men and 16 young men of normal weight to see if there were differences in how they chewed their food.

They also looked to see if chewing more would lead subjects to eat less and would affect the levels of blood sugar or certain hormones that regulate appetite.

Several previous studies have found that eating faster and chewing less are associated with obesity, while others have found no such link.

But in the current study, the team found a connection between the amount of chewing and levels of several hormones that "tell the brain when to begin to eat and when to stop eating," co-author Shuran Wang said in an e-mail.

More chewing was associated with lower blood levels of ghrelin, a hormone that stimulates appetite, as well as higher levels of CCK, a hormone believed to reduce appetite.

These hormones may represent "useful targets for future obesity therapies," Dr. Wang added, since regulating their levels may help people control their appetites.

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The authors found no difference between the size of bites taken by obese or normal-weight men, and no link between chewing duration and blood sugar or insulin levels in any of the men.

Since the study was small and included only young men, it does not necessarily predict how extended chewing will affect the calorie intake of other people, the authors noted.

But the 12-per-cent calorie reduction for the people who chewed their food 40 times could potentially translate into significant weight loss - with average people who cut their calorie intake by that much losing nearly 25 pounds in a year, said Adam Drewnowski, director of the University of Washington Center for Obesity Research in Seattle.

But since the typical diet includes foods that are not chewed, such as soup and ice cream, the actual amount of weight one is likely to lose by chewing more is much less, he warned.

"I suppose that if you chew each bite of food 100 times or more you may end up eating less, However, I am not sure that this is a viable obesity-prevention measure," said Dr. Drewnowski, who was not involved in the study.

However, the authors said the relationship between eating behaviours and obesity is worth studying further.

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