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.
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.
Murakami
Kentaro
K
Nutritional Epidemiology Program, National Institute of Health and Nutrition, Tokyo, Japan.
Sasaki
Satoshi
S
Takahashi
Yoshiko
Y
Uenishi
Kazuhiro
K
Yamasaki
Mitsuyo
M
Hayabuchi
Hitomi
H
Goda
Toshinao
T
Oka
Jun
J
Baba
Keiko
K
Ohki
Kazuko
K
Kohri
Toshiyuki
T
Muramatsu
Kanako
K
Furuki
Mika
M
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