title: Hardness (difficulty of chewing) of the habitual diet in relation to body mass index and waist circumference in free-living Japanese women aged 18-22 y.
abstract: BACKGROUND
  Animal studies suggest the beneficial effect of hardness of diet on body weight and adiposity. No human studies have examined hardness of diet in relation to obesity.
  
  
  OBJECTIVE
  We examined cross-sectional associations of hardness of the habitual diet with body mass index (BMI; in kg/m(2)) and waist circumference in free-living humans.
  
  
  METHODS
  Subjects were 454 female Japanese dietetic students aged 18-22 y. Dietary hardness was assessed as an estimate of masticatory muscle activity for the habitual diet (ie, the difficulty of chewing the food). The consumption of a total of 107 foods was estimated by means of a self-administered, comprehensive diet history questionnaire, and masticatory muscle activity during the ingestion of these foods was estimated according to published equations. Waist circumference was measured at the level of the umbilicus.
  
  
  RESULTS
  Mean BMI was 21.4 (95% CI: 21.1, 21.6), and mean waist circumference was 73.6 (72.9, 74.3) cm. Mean dietary hardness was 178 (175, 181) mV x s/1000 kcal. Dietary hardness was not significantly associated with BMI. However, it was negatively associated with waist circumference (P for trend = 0.005). This association remained after adjustment not only for potential confounding factors (P for trend = 0.028) but also for BMI (P for trend = 0.002).
  
  
  CONCLUSIONS
  Whereas no association between dietary hardness and BMI was seen, increasing dietary hardness was associated with lower waist circumference even after adjustment for BMI in free-living young Japanese women. This finding could make innovative contributions to the literature and raise issues for future studies regarding diet and obesity.
authors.affiliation: Nutritional Epidemiology Program, National Institute of Health and Nutrition, Tokyo, Japan.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Murakami
authors.forename: Satoshi
authors.initials: S
authors.lastname: Sasaki
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Uenishi
authors.forename: Mitsuyo
authors.initials: M
authors.lastname: Yamasaki
authors.forename: Hitomi
authors.initials: H
authors.lastname: Hayabuchi
authors.forename: Toshinao
authors.initials: T
authors.lastname: Goda
authors.forename: Jun
authors.initials: J
authors.lastname: Oka
authors.forename: Keiko
authors.initials: K
authors.lastname: Baba
authors.forename: Kazuko
authors.initials: K
authors.lastname: Ohki
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Kohri
authors.forename: Kanako
authors.initials: K
authors.lastname: Muramatsu
authors.forename: Mika
authors.initials: M
authors.lastname: Furuki
mesh_terms: D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D004032:Diet; D005260:Female; D006801:Humans; D007564:Japan / Q000453:epidemiology; D016014:Linear Models; D008409:Mastication / Q000502:physiology*; D009765:Obesity / Q000453:epidemiology / Q000209:etiology; D011795:Surveys and Questionnaires