Carbohydrate digestion time varies. Slow-digesting carbs, called complex carbs, include whole grains and vegetables; while fast-digesting carbs include refined grains and sugary foods. Bread, pasta, donuts and other baked goods made with white flour are refined grains.
Complex carbohydrates like green vegetables take approximately five hours to digest.
Overview of Digestion
Digestion is an amazingly orchestrated process that involves multiple body parts. The digestive tract includes the mouth, esophagus, stomach and small and large intestines. However the pancreas, liver and gall bladder, as well as hormones and nerves, also play a role in digesting food, says the National Institute of Diabetes and Digestive and Kidney Diseases.
Twenty-four to 72 hours are required for digestion, states the University of California at Santa Barbara. Food passes through the stomach and small intestine in six to eight hours. Afterward, it enters the large intestine, where further digestion and absorption of water occurs. Elimination of undigested food through the large intestine typically starts after 24 hours, but complete elimination can take several days.
Digestion time varies with the meal composition and the individual. Although the approximate time for sugars and fruits is two hours, the time required for mildly starchy food and green vegetables, which are nonstarchy, is five hours, states UCSB. Fats and proteins take about 12 hours to digest.
Overview of Carbohydrate Digestion
Experts at the North American Society for Pediatric Gastroenterology, Hepatology and Nutrition describe the process of carbohydrate digestion. They explain that the goal is to break down carbohydrates into components that the cells can use as an energy source.
Digestion of the foods begins in the mouth, where salivary enzymes are released during chewing. Minimal carbohydrate digestion occurs in the stomach. Once the food reaches the small intestine, digestion continues with the aid of pancreatic enzymes and other enzymes found in the small intestinal lining.
Simple carbohydrates contain either monosaccharides, which contain one type of sugar, or disaccharides, which contain two types of sugar, says the Harvard T. H. Chan School of Public Health. Because of their simple structure, they are digested quickly and easily. They cause blood sugar to spike and trigger increased insulin secretion by the pancreas, which can lead to adverse health effects.
Complex carbohydrates have a more elaborate chemical structure. These slow-digesting carbs are made of three or more sugars, called polysaccharides or oligosaccharides. Many of these foods contain vitamins, minerals and fiber, so they take longer to digest. Consequently, they don't produce an immediate effect on blood sugar, which causes it to rise more slowly rather than spike.
Read more: How Long After Eating Does Blood Sugar Peak?
How to Choose Healthy Carbs
According to the American Cancer Society, complex carbs are good-for-you carbs. Food sources include vegetables and beans. They also involve whole grains such as brown rice, oats and barley, along with bread and other baked goods made of 100 percent whole-grain or whole-wheat flour.
For the most part, simple carbs are unhealthy because they lack fiber, vitamins and minerals. Exceptions are the naturally occurring sugars found in fruit and milk, states the American Heart Association. Since fruit contains fiber and nutrients, it won't spike blood sugar like other simple sugars. Likewise, milk contains nutrients the body needs, so the sugar content doesn't have harmful effects.
Many foods are sources of simple carbs. They include white sugar, brown sugar, maple syrup, high-fructose corn syrup, sodas and candy. They also involve refined grains such as pasta, white rice and white bread, as well as products made with white flour. Most crackers, donuts, cakes, cookies and pastries are simple carbs. In addition, a host of food products contain added sugars like high-fructose corn syrup.
What do healthy carb choices look like in the diet? To start your day with a nutritious breakfast, forget about sugary pastries and go for a whole-grain food like oatmeal or whole-wheat muffins. Include a sliced banana in the oatmeal, or have a piece of fruit on the side.
To increase your intake of whole grains, select brown rice over white rice. Add bulgur wheat to salads and casseroles, and include barley in soups, suggests the American Cancer Society. When buying grain products, read labels to ensure they're made completely from whole grains rather than white flour or a mixture of the two.
Benefits of Slow-Digesting Carbs
The T.H. Chan School reports that diets rich in fruits and vegetables, which are slow-digesting complex carbs, can help protect against an array of diseases. Benefits include lowering blood pressure, suppressing appetite, improving blood sugar and preventing some types of cancer. The foods also decrease the risk of digestive maladies, eye disorders, heart attacks and strokes.
Whole grains contain bran, which is high in fiber, vitamins, minerals and phytochemicals. Fiber slows the breakdown of carbohydrates into glucose, which fosters healthier levels of blood sugar. The food constituent also reduces cholesterol, facilitates the movement of wastes through the digestive tract and helps prevent the formation of blood clots, which can lead to heart attacks and strokes.
Read more: A Complete Guide to Complex Carbohydrates
Health Effects of Simple Carbs
Eating simple carbs can lead to weight gain. The lack of fiber and nutrients cause the body to metabolize these foods into glucose rapidly which, in turn, stimulates an increase in the production of insulin, a hormone that boosts fat storage. These effects account for why such foods make weight management challenging.
Refined carbs may increase the symptoms of Type 2 diabetes. In a November 2014 study published in M_ediators of Inflammation_, researchers linked consumption of refined grains to an increased risk of insulin resistance, which is one of the main conditions associated with the disease. A March 2014 study featured in the British Journal of Nutrition found that a large intake of noodles and white rice was tied to insulin resistance and high blood glucose.
Eating too many refined carbs is also connected with an increased risk of heart issues. A December 2017 study published in Open Heart suggested that a high sugar and refined carbohydrate intake may heighten the likelihood of coronary heart disease.
- National Institute of Diabetes and Digestive and Kidney Diseases: "Your Digestive System & How It Works"
- University of California at Santa Barbara ScienceLine: "Can You Please Tell Me the Digestive Timeline for Protein, Fat, and Starch?"
- North American Society for Pediatric Gastroenterology, Hepatology and Nutrition: "Carbohydrate Digestion and Absorption"
- Harvard T.H. Chan School of Public Health: "Carbohydrates and Blood Sugar"
- American Cancer Society: "Good-for-You Carbohydrates"
- American Heart Association: "Carbohydrates"
- Harvard T.H. Chan School of Public Health: "Vegetables and Fruits"
- Cleveland Clinic: "Carbohydrates"
- Mediators of Inflammation: "Excessive Refined Carbohydrates and Scarce Micronutrients Intakes Increase Inflammatory Mediators and Insulin Resistance in Prepubertal and Pubertal Obese Children Independently of Obesity"
- British Journal of Nutrition: "Rice and Noodle Consumption Is Associated With Insulin Resistance and Hyperglycaemia in an Asian Population"
- Open Heart: "Markedly Increased Intake of Refined Carbohydrates and Sugar Is Associated With the Rise of Coronary Heart Disease and Diabetes Among the Alaskan Inuit"