Sucrose contains 50 grams of glucose and 50 grams of fructose per 100 grams but the two sugars are joined together by a chemical bond making it one molecule called sucrose. The bond has to be broken in digestion in order to separate glucose from fructose. Sucrose is absorbed in the small intestine. The glucose and fructose molecules are not released as individual molecules until they reach the blood stream. It rarely reaches the colon.
Potato & wheat starch are similar to corn starch. They contain similar amounts of glucose which is close to 99%. By definition starch is a carbohydrate consisting of a large number of glucose molecules joined together by chemical bonds.
Glucose is rapidly absorbed small intestine. In the amounts normally consumed it rarely, if ever, reaches the colon. An IV given in a hospital frequently contains glucose as well as electrolytes and water. It is an important fuel for the body. It is not known to directly have negative effects on IBS symptoms.
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