The effect of whole wheat and wheat milling fractions on metabolic parameters of adiposity, glucose control, and lipid metabolism using a rat model of obesity with type 2 diabetes

Obesity prevalence is at an all-time high, with 1 in 3 Americans now classified as obese (1). Obesity is a debilitating condition that is associated with various co-morbidities, including type 2 diabetes (T2D), cardiovascular disease, pulmonary dysfunction, gastrointestinal disease, various cancers, and osteoarthritis. T2D is one of the most significant co-morbidities of obesity, as it often leads to other diseases such as non-alcoholic fatty liver disease (NAFLD) and hyperlipidemia.;Several epidemiological studies suggest that whole grain consumption is associated with a lower risk of obesity and T2D. Whole grain consumption has been found to have an inverse association with fat mass and insulin resistance in both humans and rats, possibly through several different mechanisms, involving mechanical, hormonal, and anti-inflammatory processes. The mechanical mechanism focuses on alterations in caloric density and absorption of nutrients, the hormonal mechanism on changes in hormone synthesis and secretion due to nutrient availability, and lastly, anti-inflammatory and anti-oxidative components in the whole grain. However, it is unclear which milling fraction of the whole grain, the bran, germ, or endosperm, may be responsible for these health benefits.;Therefore, the aim of this study was to examine the effects of whole wheat and wheat milling fractions, specifically bran, germ, and endosperm, on glucose control, insulin resistance, fatty liver, and adiposity using an animal model of obesity with T2D, the Zucker Diabetic Fatty (ZDF) rat. Male ZDF rats were fed either a cornstarch-based diet (AIN-93G; obese control ), or diets containing 64% whole wheat flour, 54% refined wheat, 9.4% wheat bran, 1.6% normal wheat germ, or high 15% wheat germ for 5 weeks. Lean ZDF littermates fed a standard AIN-93G diet served as a negative control. All animals were fed ad libitum. The refined wheat, wheat bran, and wheat germ were present in the diets in the same concentration as would be found in the whole wheat diet. The high wheat germ diet had amounts of germ 10 times that of the normal wheat germ diet. It was found that after 5 weeks, the whole wheat, refined wheat, and high and normal wheat germ groups all showed a significant improvement (p<0.05) in area under the curve during glucose and insulin tolerance tests. There were no differences in body weight or fat pad weight among the ZDF groups; however, there was a significant difference (p=0.031) in fat mass % between the whole wheat group and the obese control. The whole wheat group and all wheat fraction groups decreased the concentration of liver lipids compared to the obese control, and the bran and germ groups also had lower liver cholesterol concentration. Only the whole wheat group had a significantly lower cecum pH (p<0.0001) and greater cecal weight (p<0.0001) compared to the obese control, indicating greater fermentation of the diet. There were no significant differences in plasma adiponectin and resistin levels among the ZDF diet groups. In conclusion, the results of this study suggests that none of the wheat milling fractions stand out as responsible for the metabolic effects seen with consumption of whole wheat and that individual milling fractions of wheat are just as effective in improving insulin resistance and fatty liver as whole wheat. (Abstract shortened by UMI.).