The average meal requires a lot sorting out once it enters the stomach and small intestine. It's unlikely that you consume just one type of food at a time, or a food that contains just one type of carbohydrate, protein or fat. Yet even though the entire meal enters on the same timetable, different parts absorb at different times, because they require varying amounts of digestion.
Carbohydrate Types
Carbohydrates require the least digestion of any type of food, with foods that contain simple carbohydrates, also known as simple sugars or monosaccharides, absorbing through the digestive tract faster than any other food. Glucose, a simple sugar, absorbs into the bloodstream in less than a minute. Foods that contain complex carbohydrates, such as whole grains, take longer to digest and assimilate than simple sugars, but less time than proteins or fats. One type of carbohydrate, fiber, found in fruits, vegetables and whole grains, doesn't break down for absorption at all. Fiber passes undigested through the intestine in the stool.
Carbohydrate Breakdown
Foods that consist of simple sugars, like candies or soda, eaten alone digest rapidly; 100 g of maltose digests within five minutes, 100 g of sucrose within seven minutes, and 100 g of lactose within 10 minutes, according to Steve Denham of Monsanto. Starches take around 75 minutes to pass through the small intestine; by the time they reach the end, between 80 to 90 percent will have digested.
Proteins and Fats
Proteins break down for absorption more quickly than fats, which remain in your digestive tract for the longest amount of time, since they're absorbed in the farthest end of the small intestine, the ileum. Amino acids in proteins are normally used to repair tissues, not to serve as an energy source. Fats supply an alternative fuel source if you don't have enough carbohydrates on hand to supply your needs.
Considerations
If you eat a meal consisting of nothing but simple sugars, your blood sugar levels may rise higher than they would if you added protein and fats to your meal, a situation that over time can make you susceptible to type 2 diabetes. You're more likely to feel hunger pangs within a shorter amount of time after an all-carb meal that doesn't include complex carbs or fiber. If you're diabetic and have low blood sugar levels, medically termed hypoglycemia, eating a simple sugar will raise your blood glucose very quickly.
References
- National Institute of Diabetes and Digestive and Kidney Diseases; Your Digestive System and How It Works; April 2008
- Ask Dr. Sears: What Is Digestion?
- MadSci Network; How Long Does It Take Carbohydrates to Be Digested?; Steve Denham; April 2005
- Children's Hospital and Regional Medical Center; Short Gut Syndrome; Lori S. Brizee, R.D.
- "The Merck Manual Home Health Handbook"; Carbohydrates, Proteins, and Fats; Margaret Mary Wilson, M.D.; July 2008
