The typical person chews their food 15 times. A study published in the American Journal of Clinical Nutrition found that when chewing was increased to 40 times, study participants ate less; 12% fewer calories. 

Why does chewing more cause you to eat less? It has to do with hormone balance. When you take time to chew your food, your body can regulate your appetite and hunger more efficiently. Chewing more caused a decrease in the hormone ghrelin, an appetite  stimulant, and a increase in the hormone CCK, an appetite suppressant. In other words, when you chew more, your brain knows that food is coming in and tamps down your hunger so that you don’t over-eat.

If you eat too fast your body doesn’t have time to register the fact that there is food coming in. You may still feel hungry, but that is because you didn’t give your brain enough time to send out appetite suppressing hormones, so the response is delayed and you eat more than your body needs.

You can use this information to your advantage and regulate your own hormone levels to control your appetite. Take time to eat and chew your food, you’ll have a better idea of your body’s needs and your own hunger cues.

Also, back to that 12% calorie reduction in people who took time to chew more — If the average person cut out 12% of their calorie intake, they would lose 25 pounds in one year. Wow! Not only could chewing aid in weight loss, it also helps with digestion. Proper digestion starts in the mouth. Chewing your food completely makes it easier for you to absorb nutrients and your gut doesn’t have to work as hard.

source: Can Chewing More Help You Eat Less