It has been known that chemical properties of foods control feeding behavior. For example, when animals are deficient in nutrition, they choose the foods which contain deficient nutrition selectively. On the other hand, neophobia and conditioned taste aversion work to avoid the food poisoning. Recently we found physical properties of foods, such as hardness and temperature, also affect the food choice. In this review, we demonstrate how chemical and physical properties of foods control feeding behavior.

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The goal of this study is to evaluate mastication quantities for the entire meal using electromyography (EMG). Using the EMG and video techniques, we analyzed mastication behaviors while two Japanese-style and two Western-style meals were being eaten. The mastication quantities of rice and bread, the staple foods in the meals, were compared.
Bread was softer in mechanical test than rice, but EMG activity of bread was higher than that of rice. Balance in mastication quantities was good in Japanese-style menus, while in Westernstyle menus including bread, more mastication was required for bread.
In the case of French bread, the hardness determined by the standards of the Ministry of Health, Labour and Welfare was appropriately low for elderly persons, however French bread required quite high amount of chewing. As mastication quantity in bread is high, westernized food would not reduce mastication.
Rice gruel is cooked to soften the cooked rice. As a larger volume of gruel is required to provide the equivalent energy of rice, more chewing with long mastication was needed to intake the required energy. This fact suggests that softer food is not always easier to chew.

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It is well known that insulin secretion is affected by inheritance, obesity, aging and the other factors, but quite a few studies have been made on the relation between mastication and insulin secretion. Since mastication is the first process of ingestion, we took it into consideration, especially occlusal conditions. Our previous research revealed that the occlusal conditions made a significant difference between normal-occlusion subjects and mal-occlusion subjects in insulin secretion and insulin sensibility.
However, it was not clear whether this result was due to the difference of crushing ability of food or mastication ability. To investigate the influence of the stimulation of masticating on insulin secretion, we measured the plasma insulin while healthy and non-obesity subjects were masticating gum base that did not include sweetener and flavor.
As a result, there was no change in plasma glucose level from pre-mastication to 15 min after masticating, and interaction was not shown between control group and gum-masticating group. There were significant difference in plasma insulin level from pre-mastication to 15 min after masticating, and interaction was shown between control group and gum-masticating group.
This result suggested that the stimulation by the mastication participate the insulin secretion.

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