Factors Affecting Viscosity of Select Dietary Fibers, Complete Food Matrices, and Canine Ileal Digesta
Little data exist on the influence of dietary factors on viscosity of gastrointestinal tract contents. In addition, a standardized method of gastrointestinal tract viscosity measurement has not been established. In Study 1, fibers were subjected to a two-stage in vitro gastric and small intestinal simulation model. Viscosities were measured at multiple shear rates. Viscosities of all fiber solutions were dependent on shear rate and were concentration-dependent. During gastric simulation, viscosity was higher at 2 and 4 h compared with 0 h for all fibers except psyllium that had higher viscosities at 6 h (P<0.05). During small intestinal simulation, viscosities peaked between 6 and 15 h; however wood cellulose solution viscosity did not change over time. In Study 2, mixer viscometry was applied to canine ileal digesta to determine the effect of various diets on canine ileal and simulated gastric and small intestinal digesta viscosity. Ileal digesta averaged 15.938 and 9,746 cP when dogs were fed a standard diet or test diets, respectively. High-fat, high-protein diets promoted high viscosities at 0 and 2 h compared with diets containing high total dietary fiber during gastric digestion simulation. Viscosity peaked between 6 and 9 h of small intestinal digestion simulation. During Study 3, four experiments were conducted to determine dietary factors affecting digesta viscosity of dogs. Ileal digesta viscosity tended to be higher (P=0.07) for full-fed (10,251 cP) compared with restricted-fed dogs (6,677 cP). Ileal digesta viscosities were 6,561, 11,074, 13,830, and 15,967 cP for dogs consuming insoluble dietary fiber, soluble dietary fiber, animal protein, and plant protein diets, respectively. Ileal digesta viscosities ranged from 1,326 to 46,641 cP and 7,748 to 10,208 cP for canned and dry diets, respectively. Collectively, these data suggest that consumption of viscous fibers and other dietary factors such as food intake, and diet matrix affect viscous characteristics of gastrointestinal tract contents. The next step is to couple knowledge of gastrointestinal tract viscosity characteristics with desired physiological outcomes. Data indicate that mixer viscometry is useful for measuring viscosity of canine ileal digesta.
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