Abstract
It has been suggested recently that high-fiber diets may be beneficial for diabetics since they reduce the postprandial blood glucose and serum lipid levels, but their exact mechanisms of action have not yet been clarified.
We have studied the treatment of diabetics with Konjac Mannan (Glucomannan). Like Guar Gum, Glucomannan has proved useful in the treatment of diabetics. We therefore compared the effects of Glucomannan and Guar Gum on the blood glucose and serum insulin levels after test meals, in particular examining the effects of their viscosity.
When 3.9 g of Glucomannan was mixed into the test meals of 6 non-insulin dependent diabetics, the mean blood glucose level was significantly below that of the control at 30 and 60 min. However, when 3.9 g of Guar Gum was given in the same way as Glucomannan, no significant reduction in mean blood glucose level was seen during the observation period.
It appeared that the viscosity of the fiber within the gastrointestinal tract might be an important factor in flattening the curves of the postprandial blood glucose levels. The viscosities of three kinds of fibers were therefore examined. The viscosity of 1 % highly purified Glucomannan solution reached 194, 800 cps, whereas those of 1 % Guar Gum and 3 % Pectin solution were only 7, 700 and 2, 429 cps, respectively, as measured with a B-type viscometer. Glucomannan's viscosity was thus the highest among the three.
The effects of differences in viscosity were examined using two types of Glucomannan. When highly purified high viscosity Glucomannan (194, 800 cps) was added to the test meals and given to 9 normal subjects, no significant rise in the mean postprandial blood glucose level was observed. On the other hand, when low viscosity Glucomannan (55, 000 cps) was given in the same way, the mean rate of postprandial rise in glucose level was almost the same as in the control. Glucomannan was thus more effective at high viscosity than at low. Xylose absorption tests showed that viscous forms of dietary fiber prolonged the time required for absorption and reduced the postprandial rise of glucose, rather than causing malabsorption. Thus, the most viscous of the dietary fibers, purified Glucomannan, was the most effective in suppressing the postprandial rise of blood glucose and this suppression appeared to be related to its very high viscosity.
