Lifestyle related disease is a generic term for diseases such as cardiovascular diseases, diabetes mellitus and cancer caused by life style or life habit, and one of its fundamental causes is obesity. The reason why most people put on weight after their middle age is mainly because of the increase of visceral fat by the decrease in basal metabolism and the amount of momentum despite of unchanging appetite. Due to this sequence of weight gain, after middle age upper respiratory tract becomes narrower, and it worsens obstructive sleep apnea syndrome (OSAS). Since mastication is to provoke and maintain arousal, OSAS patients, who especially feel strong sleepiness, tend to encourage them to be obesity by frequent mastication that leads them to the tendency to overeat. Two main symptoms of OSAS are snoring and sleepiness; however, the essence of sleepiness is the worse quality of sleep due to apnea. In addition, a vicious circle is eventually generated because sleep deprivation and sleep disorders affects hypertension and glucose intolerance, and those worsen lifestyle disease. In order to break this off, it is necessary to review life style and habit, and improve not only on diet and exercise therapy but also on sleep.