A potato holds no glucose you can use. Starch is thousands of glucose rings chained together, and only single rings cross the intestinal wall — so between the plate and the bloodstream sits a chain of enzymes, each one cutting a bond the last one couldn't. Walk the route from mouth to blood, then run the numbers on a meal and watch grams of starch become grams of glucose.
The route
Starch to glucosechoose a station on the route
Enzyme—
pH here—
Absorbable?—
Starch broken down to free glucose0%
Starch in the mealgrams, as eaten50 g
Resistant fractionescapes the small intestine8%
Free glucose released51.1g
Approximate portions — tap to load
Portion figures are rough averages for a typical serving, not measurements of any particular food. Cooking, cooling, ripeness and processing all shift the resistant fraction.