Dietary fat in midlife has not been associated with breast cancer risk in most studies, but few have followed women beyond one decade. The authors examined the relation of dietary fat, assessed by repeated questionnaires, to incidence of postmenopausal breast cancer in a cohort of 80,375 US women (3,537 new cases) prospectively followed for 20 years between 1980 and 2000. The multivariable relative risk for an increment of 5% of energy from total dietary fat intake was 0.98 (95% confidence interval: 0.95, 1.00). Additionally, specific types of fat were not associated with an increased risk of breast cancer. Furthermore, secondary analyses indicated no differences in breast cancer risk by estrogen receptor or progesterone receptor status. However, stratification by waist circumference indicated a significant decrease in breast cancer risk for participants with a waist circumference of 35 inches (88.9 cm) or greater (p-trend = 0.04). None of the latency intervals investigated were associated with an increased risk of breast cancer. In addition, fat intake before menopause was not related to risk of postmenopausal breast cancer. These results suggest a reduction in breast cancer risk for women with insulin resistance syndrome who consume high-fat diets and no association between specific sources of fat during midlife and risk of postmenopausal breast cancer.
There is an increasing awareness of the link between food breakdown during chewing and its nutrient release and absorption in the gastrointestinal tract. However, how oral processing behaviour varies among different ethnic groups, and how such difference further impacts on bolus characteristics and consequently glycemic response (GR) are not well understood. In this study, we recruited a group of Asian (Chinese) subjects in China (n = 32) and a group of Caucasian subjects in New Zealand (n = 30), both aged between 18 and 30 years, and compared their blood glucose level (BGL) over 120 min following consumption of a glucose drink and cooked white noodles. We also assessed their chewing behaviour, unstimulated saliva flow rate, and ready-to-swallow bolus characteristics to determine whether these measures explain the ethnic differences in postprandial glycaemia. Compared to New Zealand subjects, the Chinese subjects showed 35% slower saliva flow rate but around 2 times higher salivary α-amylase activity in the unstimulated state. During consumption of noodles, Chinese subjects on average took a larger mouthful size, chewed each mouthful for longer and swallowed a larger number of particles with a smaller particle size area. Total GR measured by area under the curve (IAUC) was higher among the Chinese subjects. They also experienced higher BGL at 15 min, as well as higher peak BGL. There were strong correlations observed between oral processing and GR parameters. Results of this study confirmed the significance of oral processing in determining food digestion, and will provide new insights on the role of ethnicity in influencing people's physiological response to food.
It is important to understand variability in consumer chewing behavior for designing food products that deliver desired functionalities for target consumer segments. In this study, we selected 29 participants, representing the large range of chewing variation we had observed in 142 healthy young adults, and investigated the influence of chewing behavior on gastrointestinal digestion and colonic fermentation, using in vitro models and brown rice as a model food. Chewing behavior measured by video observations and chewing outcome differed widely between participants, resulting in large differences in the digestibility of carbohydrates. Inter-individual differences in chewing behavior and chewing outcome also significantly affected in vitro patterns of microbial composition and the production of organic acid metabolites, resulting from colonic fermentation, which is increasingly recognized to be important for human health. These digestion/fermentation outcomes were largely related with the chewing time per mouthful, proportion of bolus particles bigger than 2 mm and amount of saliva added to the bolus during chewing. No significant relationships were found with other chewing trajectory and oral physiological measures. These results suggest that modification of chewing may be an effective strategy to control blood glucose levels and to shape gut microbiota and their metabolites, without altering diets, and that further in vivo studies are warranted to confirm these in vitro findings.
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