Dietary fibers with high viscosities may promote greater satiety and weight loss than fibers with low viscosities suggesting that the physicochemical properties of a fiber contribute to its satiety promoting effects. We measured physicochemical properties of arabinoxylans both separate and incorporated in a flaked cereal, and related these properties to appetite in two clinical trials. The impact of a steam pressure-cooking process on physicochemical properties of ready-to-eat (RTE) cereal with 15% added fiber as an intact arabinoxylan from flax (FLAX) or an enzyme hydrolyzed arabinoxylan from wheat (AXOS) versus a low fiber control RTE cereal was evaluated. Peak molecular weights of intact and hydrolyzed fibers were ~2.9x106 and ~800 g/mol, respectively, with a ~400-fold higher viscosity for intact fiber. As a result of the steam pressure-cooking process used, the molecular weight of intact (FLAX) fiber was reduced to approximately the molecular weight of hydrolyzed (AXOS) fiber. Consistent with molecular weight reduction, there was only a 2-fold difference in viscosity between the 2 high-fiber RTE cereals. The low fiber (4%) control RTE cereal, due to greater starch content, had higher viscosity than either of the 2 high fiber RTE cereals. Effects of these two high-fiber RTE breakfast cereals as compared with a lower fiber RTE cereal on perceived appetite, hormone responses, and lunch meal energy intake in overweight women (BMI 25.0-29.9 kg/m2) were evaluated. Two randomized, double-blind, crossover design trials (n=30, n=35 subjects, respectively) were completed. All 3 breakfast meals (100 g RTE cereal) were standardized for a total mass of 500 g with milk and water. Perceived appetite was assessed before and after breakfast, at specific times throughout the testing day. No differences in perceived appetite were observed among breakfast meals in either trial. At 240 min, the subjects were provided with an ad libitum macaroni and cheese lunch. Subsequent lunch energy intake was not different after any of the breakfast meals in either trial. In addition to the previous procedures, blood samples were collected up to 4 h after breakfasts in trial 2 for assessments of plasma glucose, insulin, active ghrelin, active GLP-1, and total PYY concentrations. Both high-fiber breakfast meals increased post-breakfast GLP-1 and PYY concentrations compared with the low-fiber RTE cereals possibly due to fermentation and production of short chain fatty acids. Cereal processing reduced the molecular weight of intact fiber and viscosity of the RTE cereal from a predicted >160,000 to ~5,000 mPa∙s. This viscosity was lower than in the control RTE cereal (~9,000 mPa∙s), and significantly less than viscosity demonstrated in beverages to affect satiety. Fifteen grams of soluble low molecular weight fiber added to RTE cereal did not increase viscosity enough to affect perceived appetite or energy intake at lunch despite differences in satiety hormone signaling in overweight females. Subjects were not sensitive enough to the different satiety hormone signaling cues to affect their perceived appetite or lunch energy intake.
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