In-Depth Notes on Carbohydrates

Overview of Carbohydrates

• Definition: Carbohydrates are a class of energy-yielding nutrients composed of carbon, hydrogen, and oxygen (often abbreviated as CHO).
• Classification:
  • Simple Carbohydrates: Contain one or two sugar molecules.
  • Complex Carbohydrates: Composed of many sugar molecules, include starch, glycogen, and fiber.

Types of Carbohydrates

• Monosaccharides:

  • Simplest form of carbohydrates with individual sugar molecules.
  • Common types:
  • Glucose:
    • Also known as dextrose, key component of all disaccharides, and the primary sugar produced from digestible carbohydrates.
  • Fructose:
    • Known as fruit sugar, the sweetest natural sugar, and found in high-fructose corn syrup (HFCS).
  • Galactose:
    • Not found in significant quantities in foods; combines with glucose to form lactose.

• Disaccharides:

  • Composed of two linked monosaccharides.
  • Examples include:
  • Sucrose:
    • Composed of glucose and fructose; naturally occurring in fruits and vegetables.
  • Maltose:
    • Made of two glucose molecules; not typically found in natural foods.
  • Lactose:
    • Milk sugar, composed of glucose and galactose; natural source in milk, the least sweet disaccharide.

• Polysaccharides:

  • Complex carbohydrates that do not have a sweet taste and are abundant in large quantities:
  • Starch:
    • Form in which glucose is stored in plants; major part of diets from grains and legumes.
  • Glycogen:
    • Animal form of starch; stored in liver to release glucose into the bloodstream.
  • Fiber:
    • Indigestible polysaccharides; crucial for digestive health, categorized into dietary and functional fiber.

Sources of Carbohydrates

• Natural Sources: Grains, legumes, certain vegetables, and naturally occurring sugars in milk and fruits.
• Added Sugars: Sugar incorporated during processing, can contribute to increased calorie intake without additional nutrients.

Digestion and Absorption

• Process:

  • Begins in the mouth with salivary amylase acting on cooked starch.
  • Most digestion occurs in the small intestine.
  • Monosaccharides are absorbed through intestinal cells and transported to the liver.
  • Undigested starches pass to the colon and are excreted.

• Fiber's Role:

  • Non-digestible fibers reach the large intestine, attract water to soften stools, and some are fermented to produce short-chain fatty acids used for energy.

Metabolism of Carbohydrates

• Glucose Formation: Fructose and galactose convert to glucose in the liver, which regulates blood sugar levels.
• Insulin and Glucagon:
  • Insulin released by the pancreas lowers blood glucose levels after meals.
  • Glucagon maintains blood glucose levels during fasting periods by stimulating liver glucose release.

Functions of Carbohydrates

• Energy:
  • Carbohydrates provide 4 kcal/g; essential for cellular processes, particularly in the brain which relies solely on glucose.
• Protein Sparing:
  • Adequate carbohydrate intake prevents muscle breakdown for energy.
• Preventing Ketosis:
  • Adequate glucose prevents the production of ketone bodies that can lead to ketoacidosis and related symptoms like nausea and fatigue.

Dietary Recommendations

• Recommended Daily Allowance (RDA):
  • 130 g of carbohydrates for adults and children, representing 45%-65% of total calorie intake.
• Fiber Intake:
  • 14 g per 1000 calories; approximately 25 g/day for women and 38 g/day for men.

Health Promotion and Tips

• Carbohydrate Choices:
  • Focus on whole grains over refined grains, limit added sugars, and consume a variety of fruits and vegetables.
• Increasing Fiber Intake:
  • Substitute refined grains with whole grains, choose fiber-rich cereals, and gradually increase fiber consumption along with fluid intake.
• Reduced Added Sugars:
  • Choose sugar alternatives (like sugar alcohols) that provide sweetness without spikes in blood glucose.

Managing Carbohydrates in Diabetes

• Diabetic diets now focus on consistent total carbohydrate intake with flexibility regarding types of carbohydrates, allowing for some sweets within healthy diets.

• Key Changes:

  • Emphasis on overall carbohydrate management rather than restricting simple sugars solely.