Potatoes are rich in starch. During digestion, starch breaks down into glucose, which enters the bloodstream. This process is measured using the glycaemic index, or GI. Foods with a high GI raise blood sugar quickly, while low-GI foods raise it more slowly, as per Medlineplus. Potatoes naturally sit in the medium-to-high GI range, but cooking style can push them higher or pull them down.
