Primarily made up of carbohydrates, fruit digests relatively quickly. That's because carbohydrates are the most quickly digested of the three macronutrients -- protein, fat and carbs. Some carb foods digest more quickly than others, however, depending on their nutrient makeup. Fruits higher in fiber will digest more slowly, while fruits higher in sugar will digest more rapidly.
Your first bite of fruit marks the beginning of digestion. Your salivary glands release a specialized enzyme called salivary amylase that goes to work on the bonds holding together the sugars making up carbohydrates. The fruit then passes through your esophagus to your stomach and then to your small intestine, where another enzyme called pancreatic amylase is released and continues to break down the carbohydrates. Enzymes that line the small intestine complete the breakdown of carbohydrates into a small enough form to be absorbed through the wall of the small intestine into the bloodstream.
The Fiber Factor
One type of carbohydrate, called fiber, is not completely broken down during digestion and passes through your system mostly unchanged. It also works to slow digestion, meaning a food with more fiber takes longer to digest than a food without much fiber. Most fruits are a good source of fiber, but the amount they contain will affect how quickly they are digested. For example, a small apple without the skin contains 1.7 grams of fiber, but a small apple with its skin still intact contains 3.6 grams, so the skin-on apple will digest more slowly. Other high-fiber fruits include raspberries, blackberries and blueberries. Fruits with less fiber include very ripe apricots, cantaloupe, honeydew melon and watermelon. Canned fruits without skin are also slightly lower in fiber.
Simple vs. Complex Carbs
All carbs, except fiber, are made up of sugars. Some are made up of one or two sugars, while others are composed of many sugars linked together. The more sugars a carbohydrate has, the more "complex" it is and the longer it will take to be broken down. In addition to their fiber content, fruits contain mostly the "simple" types of carbs in the form of the fruit sugar fructose. Fructose is a monosaccharide, which means it's composed of a simple sugar. Your body doesn't have to do much to break down the sugars in fruits -- they are almost immediately absorbed into your bloodstream for energy. A few fruits are higher in starches, which are polysaccharides, and will take longer to digest. An example is the plantain, which contains 22 grams of starch per cup of sliced fruit.
When to Eat Certain Fruits
Fruit can make an excellent pre- or post-workout snack, depending on its transit time and when you eat it. You can eat fruit as part of a meal about two to three hours prior to your workout for a quick source of energy. Eating a piece of fruit -- especially one with a lot of fiber -- too close to your workout may cause you to experience stomach upset because the fruit has not fully digested. Right before a workout, the Precision Nutrition website recommends blending fruit into a smoothie -- once in liquid form, the fruit is more quickly digested.
- Merck Manuals: Carbohydrates, Proteins, and Fats
- Wisc-online: Carbohydrate Digestion
- MedlinePlus: Soluble vs. Insoluble Fiber
- USDA National Nutrient Database: Apples, Raw, Without Skin
- USDA National Nutrient Database: Apples, Raw, With Skin
- USDA National Nutrient Database: Plantains, Raw
- Precision Nutrition: Workout Nutrition Explained
- Today's Dietitian: The Top Fiber-Rich Foods List
- MedlinePlus: Low-Residue Fiber Diet