Why does fructose have a low glycemic index?

• A. Because it converts to fat in the liver instead of going to the bloodstream
• B. Because it is rapidly absorbed into the bloodstream
• C. Because it raises insulin levels more than glucose
• D. Because it is metabolized by the brain without affecting blood sugar

Answer: (D)

Glycemic index measures how quickly a carbohydrate raises blood glucose after eating. Fructose yields a low response because its path in the body is different from glucose: after absorption, most fructose is taken up by the liver via the portal vein, not released into the bloodstream as glucose right away. In the liver, fructose is converted into intermediates that can become glucose, glycogen, lactate, or fat, but this happens without causing a rapid spike in blood glucose. Since blood sugar doesn’t rise quickly, insulin secretion isn’t strongly triggered either, contributing to a low GI. The idea that fructose is metabolized by the brain to avoid affecting blood sugar isn’t accurate—the brain relies primarily on glucose for energy, and fructose isn’t used by the brain in a way that would drive a low blood sugar response.