In general, it takes around 50 hours for fruit to completely digest and move through the entire digestive tract. However, sugar from ingested fruit can move from the digestive tract to the bloodstream in only 15 minutes, particularly if the fruit is taken as juice.
The glycemic index indicates how long it takes for sugars from a fruit to be absorbed and start to affect blood sugar levels. The higher the glycemic index, the faster the sugar is digested. Bananas have a very high glycemic index and grapefruits have a low one.
The time required to digest foods is also affected by the composition of the meal. For example, a meal rich in fat, fiber and protein delays gastric emptying.