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Carbohydrate Digestion

Starch to Sugar

Diagram of corn digesting to starch to maltose to glucose. Corn digests to sugar
To discuss carbohydrate digestion, let's start with the example of corn starch being broken down into glucose. You can see this process by looking at the diagram to the right (click the image to enlarge).

Inside the corn kernel is starch. Starch is represented by the blue hexagonal shapes linked together. Remember, starch is essentially glucose (sugar) linked together. Starch digestion starts in the mouth with the enzyme salivary amylase. The enzyme is like a little hacksaw, chopping off fragments of the large starch molecule into smaller segments. Very little starch digestion occurs in the stomach, but amylase stays activated until low pH, essentially the acidity of  the stomach denatures (inactivates) it. More on this later!

Once the starch fragments leave the stomach, they enter the small intestines. The starch segments, which are essentially glucose chains, are further broken down to maltose and then glucose. Maltose is a disaccharide and a simple carbohydrate (CHO). Glucose is a single sugar unit, or monosaccharide, also known as a simple carbohydrate (CHO).

Let's take a look at the various types of carbohydrates and how they are digested. Looking at the diagram below:
Candy digested to sucrose then glucose and fructose; milk digested to lactose then glucose and galactose; bagel digested to starch then malose and glucose
Let's start with the image on the left, a piece of candy. Candy is mostly made up of sucrose. Sucrose breaks down to glucose and fructose. Next, look at the center diagram. Milk breaks down to lactose which then breaks down to glucose and galactose. Lastly, on the far right we have a bagel. Just like the corn discussed above, the carbohydrates in a bagel are mostly starch. Remember, starch is a chain of glucose, strung together and then stacked and branched. Starch breaks down to shorter glucose chains. This process starts in the mouth with salivary amylase. The process slows in the stomach and then goes into overdrive in the small intestines. The short glucose chains are broken down to maltose and then to glucose. 

Carbohydrate Digestion and Absorption Video

< Carbohydrates
Carbohydrate Absorption >

References

  1. Groff. J, Gropper S. Chapter 4 Carbohydrates. In: Advanced Nutrition and Human Metabolism 3rd ed. Belmont, CA. Wadsworth; 2000.
  2. Sizer FS. Whitney E. Chapter 4 Carbohydrates. In: Nutrition Concepts and Controversies 13th ed. Belmont, CA. Wadsworth; 2014.
  3. Candy, milk and bagel digestion by Christine Dobrowolski using milk by Hector Gomez, bagel modified from johnny_automatic and candy by pitr on OpenClipArt, CC0 1.0
  4. Corn to glucose diagram by Christine Dobrowolski using corn by gnokii on OpenClipArt, CC0 1.0.
Last updated April 8, 2016

Nutritional Doublethink

Nutritional Doublethink™ is the simultaneous acceptance of two contradictory beliefs about a food, "unhealthy is healthy". This website explores these contradictions and their impact on health. The information on this website is not meant to replace the advice from your doctor or dietitian.

Copyright Nutritional Doublethink™, 2017

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  • Home
  • About
  • Blog
  • Chart
  • Gallery
  • Nutrition Topics
    • Nutrition Basics >
      • Food Label
      • Nutritious Diet
      • Whole vs Processed
      • Food Choices
      • Nutrition and Disease
    • Dietary Guidelines >
      • Determining Intakes
      • Portion Size
      • Food Groups
    • Digestive Tract >
      • Digestion & Absorption
    • Carbohydrates >
      • Carbohydrate Digestion
      • Carbohydrate Absorption
      • Sugar
      • Foods with Sugar
      • Fiber
      • Glucose Regulation
      • Carbohydrate Recommendations
    • Lipids >
      • Lipid Digestion
      • Cholesterol
      • Essential Fatty Acids
      • Trans Fatty Acids
      • Lipid Recommendations
    • Protein >
      • Protein Structure
      • Protein Functions
      • Protein Digestion
      • Protein Digestibility
      • Protein Recommendations
    • Vitamins >
      • Vitamin A
      • Vitamin D
      • Vitamin E
      • Vitamin K
      • Vitamin C
      • B-Vitamins
      • Vitamin B1: Thiamin
      • Vitamin B2: Riboflavin
      • Vitamin B3: Niacin
      • Vitamin B6: Pyridoxine
      • Vitamin B9: Folate
      • Vitamin B12: Cobalamin
    • Minerals >
      • Calcium
      • Sodium
      • Potassium
      • Iron