Part Three: Carbohydrate Digestion, Absorption, and Use

Overview of Carbohydrate Digestion

• Carbohydrates consumed in food are broken down into glucose, the body's preferred form of fuel.

• The digestive process involves several steps.

Stages of Carbohydrate Digestion

1. Mouth

   • Digestion begins with mechanical and chemical processes.

     • Mechanical digestion due to chewing.

     • Chemical digestion utilizes salivary amylase, an enzyme in saliva that partially digests starch.

2. Stomach

   • No carbohydrate digestion occurs here.

   • Salivary amylase is inactivated by stomach acid.

3. Small Intestine

   • Upon entry, the pancreas releases digestive enzymes.

   • Enzymes primarily break down starch into:

     • Monosaccharides

     • Disaccharides

     • Oligosaccharides

   • Enzymes located on the brush border of the small intestine convert disaccharides into monosaccharides.

   • Monosaccharides are absorbed into capillaries lining the small intestine and transported to the liver through the bloodstream.

   • Liver converts:

     • Galactose and fructose into glucose.

4. Large Intestine

   • Fiber and resistant starch travel undigested.

   • Some fibers and resistant starches are fermented by gut microbes, producing gases and odors.

   • Insoluble fibers remain unchanged as they pass through the digestive tract.

Lactose Intolerance vs. Milk Allergy

• Lactose

  • A disaccharide found in milk and dairy products.

  • Lactase is the enzyme required to digest lactose.

• Lactose Intolerance:

  • Impaired ability to digest lactose due to insufficient lactase production.

  • Symptoms include:

    • Nausea

    • Pain

    • Diarrhea

    • Gas (from fermentation of lactose by gut microbes)

  • Nutritional concerns arise in populations reliant on milk for calcium and vitamin D.

  • Dietary strategies include:

    • Consumption of lactose-reduced or lactose-free products.

    • Calcium and vitamin D fortified products.

    • Non-dairy calcium sources.

• Milk Allergy:

  • An immune response to proteins in milk, potentially life-threatening.

  • Distinct from lactose intolerance as it involves immune system reaction rather than enzyme deficiency.

Glucose: The End Product of Digestion

• Glucose is crucial for various body functions and is the primary energy source for:

  • Brain

  • Nervous system

  • Red blood cells

• The body regulates glucose levels through:

  • Internal glucose supply management.

  • Blood glucose control.

Uses of Glucose in the Body

1. Energy Provision:

   • Cells oxidize glucose for immediate energy.

2. Storage:

   • Excess glucose converted to glycogen and stored in:

     • Liver - for general use across the body.

     • Muscles - exclusively for local muscle use.

3. Conversion to Fat:

   • Remaining glucose after glycogen stores are full can be converted to fat.

   • Most fat in adipose tissue stems from excess dietary fat, not glucose.

Response to Low Carbohydrate Intake

• Insufficient dietary carbohydrates prompt the body to:

  1. Deplete glycogen stores in liver and muscles (up to 6 hours of energy, depending on activity).

  2. Break down proteins for glucose, reducing available proteins for essential functions.

  3. Break down fats, though inefficiently, producing ketone bodies which can lead to ketosis, disrupting blood pH balance and associated with health risks.

Hormonal Regulation of Blood Glucose

• Pancreas responds to blood glucose levels, secreting:

  • Insulin: Eases glucose entry into cells; released when glucose levels rise.

  • Glucagon: Triggers liver to release glucose into bloodstream; secreted when glucose levels drop.

• The brain maintains an emergency glucose reserve during severe deprivation.

Flatulence Related to Vegetable Consumption

• Some individuals experience flatulence and bloating post-consumption of certain vegetables, notably beans.

• Causes:

  • Presence of non-digestible carbohydrates known as resistant starch or nondigestible carbohydrates (NDCs).

  • These are related to raffinose, which is not digestible by humans due to the lack of the enzyme alpha-galactosidase.

  • Indigestible carbohydrates ferment in the large intestine, causing gas production by microbes.

Vegetables Linked to Flatulence

• Common vegetables that can cause gas include:

  • Cabbage

  • Brussels sprouts

  • Kohlrabi

  • Jerusalem artichokes

  • Garlic

  • Onions

  • Parsnips

  • Scallions

  • Beetroot

  • Broccoli

  • Chicory

  • Fennel bulbs

• Despite flatulence concerns, these foods are beneficial sources of vitamins and minerals.

Strategies to Reduce Flatulence from Vegetables

1. Gradually increase intake of gas-causing vegetables, coupled with sufficient water intake.

2. Soak legumes overnight, reducing nondigestible carbs by 10%-40%.

3. Choose fermented legume products (e.g. miso, tempeh) as fermentation breaks down nondigestible carbs.

4. Add baking soda to soaking water (do not cook in it) to reduce nondigestible carbs.

5. Cook legumes adequately, achieving a reduction of 25%-35% in nondigestible carbohydrates.

6. Utilize enzyme products like Bino and Bene Assist to aid in digesting nondigestible carbs, ensuring these are taken with the food for effectiveness.