Carbohydrates Overview

Types of Carbohydrates

• Simple Sugars:
  • Small, ring-shaped molecules made of carbon, hydrogen, and oxygen.
  • Include monosaccharides (one sugar molecule) and disaccharides (two sugar molecules linked).
• Complex Carbohydrates:
  • Formed from linked simple sugars into long chains.
  • Include oligosaccharides (3-9 sugar molecules) and polysaccharides (10 or more sugar molecules).

Roles of Carbohydrates

• Provide calories/energy.
• Simple sugars:
  • Sweeten foods (e.g., lemonade, jams).
  • Balance flavors (e.g., miso soup).
  • Fuel yeast in rising dough and alcohol production.

Sources of Sugars

• Natural Sugars: Found in fruits, vegetables, grains, and animal products (milk, cheese).
• Added Sugars: Sugars added to processed foods (e.g., cereals, salad dressings).
  • Even natural sources (e.g., sugar cane, honey) are considered added sugars when processed.

Sugar Family

• Monosaccharides:
  • Glucose: Main energy source; crosses blood-brain barrier.
  • Fructose: Found in honey, fruits, root vegetables.
  • Galactose: Found in milk (as part of lactose).
• Disaccharides:
  • Sucrose: Glucose + fructose (table sugar).
  • Maltose: Two glucose molecules (found in molasses).

Complex Carbohydrates

• Oligosaccharides: Short chains (e.g., galacto-oligosaccharides in soybeans).
• Polysaccharides:
  • Starches: Important calorie source; found in rice, potatoes, wheat.
  • Dietary Fibers: Indigestible carbohydrates that aid digestion and health.

Fiber's Importance

• Slows absorption of glucose, helps maintain healthy blood sugar levels.
• Increases stool weight, prevents constipation.
• Some fibers (e.g., beta-glucan) promote heart health.

Glycosidic Bonds

• Monosaccharides link through glycosidic bonding:
  • Example Bonds:
    • Maltose: Alpha 1-4 glycosidic bond.
    • Lactose: Beta 1-4 glycosidic bond.
    • Sucrose: Alpha 1-2 glycosidic bond.

Digestion of Carbohydrates

• Enzymes break down disaccharides, oligosaccharides, and polysaccharides into monosaccharides for absorption.
• Enzymes include amylases (for starch) and specific enzymes for disaccharides (lactase, sucrase, maltase).

Metabolism of Monosaccharides

• Glucose: Stimulates insulin release, stored as glycogen.
• Galactose: Converted to glucose in the liver.
• Fructose: Broken down and converted into energy.
• All digestible carbohydrates are eventually broken down into monosaccharides for energy use or storage.

Recommended Carbohydrate Intake

• National Academies recommend carbohydrates should make up 45-65% of total calorie intake.
• Example: For a 2000 calorie diet, aiming for 1100 calories from carbohydrates (55%).
• Fiber recommendation: 28 grams/day in a 2000 calorie diet.
• Added sugars: Less than 10% of total calories (WHO, US Dietary Guidelines).
• Total sugars: Updated Canadian labels suggest about 100 grams/day (20% of a 2000 calorie diet).

Healthy Eating Tips

• Choose nutrient-rich foods: fruits, vegetables, whole grains, and dairy with fiber, starch, and natural sugars.
• Limit added sugars by reading nutrition labels and making informed choices.

Quick Recap

• Types of Carbohydrates:
  • Simple sugars (monosaccharides, disaccharides)
  • Starches (polysaccharides)
  • Fibers (partially absorbable polysaccharides)
• A healthy diet includes a variety of carbohydrates from different sources, including minimal added sugars.