Assessment of mastication and food items
Mastication was evaluated by attaching an earphone-type masticatory meter called “earable” (eRCC, Hiroshima, Japan) to the outer ear opening. It is plugged into the opening of the external auditory canal and utilizes infrared light. In addition, an optical distance sensor (LED and phototransistor) was installed to determine the number of chews and chewing duration by measuring the minute changes in the external auditory canal. The measured changes are displayed as waveforms; a proprietary algorithm is used to detect mastication and displays the mastication data on a tablet screen in real-time. Since the user is only required to wear an earphone, the device can measure masticatory indices under conditions closer to those experienced in everyday life than the conventional masticatory meters that are worn on the chin (Fig. 
Structure of the “earable” device and tablet screenThis device has a precision of at least 0.958 and a recall of at least 0.937; therefore, it can accurately measure the number of chews [For the evaluation of mastication, we used three food items [(1) A salad (39 kcal, 1.2 g of protein, 0.5 g of fat, 6.2 g of carbohydrate, and 0.2 g of salt equivalent) contains ingredients, such as shredded cabbage, that are high in fiber. (2) Rice ball (188 kcal, 5.6 g of protein, 1.6 g of fat, 37.8 g of carbohydrate, and 0.9 g of salt equivalent) is a staple food in Japanese. (3) Donuts (214 kcal, 3.0 g of protein, 10.4 g of fat, 27.4 g of carbohydrate, 26.9 g of sugar, 0.5 g of dietary fiber, and 0.5 g of salt equivalent) are readily available snacks.