Chapter 3

Title: Carbohydrates Overview

Chapter 3: Carbohydrates

  • Authors: Linda Debruyne, Kathryn Pinna

  • Edition: Seventh Edition

  • Source: © 2020 Cengage. All rights reserved.

Learning Objectives

  • Identify Carbohydrates:

    • Monosaccharides, disaccharides, polysaccharides, and their food sources.

  • Digestion and Absorption:

    • Summarize how carbohydrates are digested and absorbed in the body.

  • Blood Glucose Control:

    • Explain the role of hormones in regulating blood glucose levels.

  • Health Problems Related to Sugars:

    • Describe health issues from added sugars and the role of alternative sweeteners.

  • Health Benefits of Starches and Fibers:

    • Identify benefits and recommendations regarding starches and fibers.

  • Glycemic Index:

    • Discuss the glycemic index and its controversial role in disease prevention.

Introduction to Carbohydrates

  • Energy Source:

    • Carbohydrates are essential for energy, especially for the brain.

    • Recommended sources include grains, vegetables, legumes, fruits, and milk.

The Chemist’s View of Carbohydrates

Types of Carbohydrates

  • Sugars:

    • Monosaccharides: Single sugars (e.g., glucose, fructose, galactose)

    • Disaccharides: Two linked sugars (e.g., sucrose, lactose, maltose)

    • Polysaccharides: Chains of monosaccharide units (e.g., starch, glycogen, fibers)

Monosaccharides Detailed

  • Glucose:

    • Key energy source, particularly for the brain and nervous system.

  • Fructose:

    • Found in fruits, honey; sweetest sugar.

  • Galactose:

    • Part of lactose, found mainly in milk.

Disaccharides Explained

  • Sucrose:

    • Composed of glucose and fructose (table sugar).

  • Lactose:

    • Made of glucose and galactose (milk sugar).

  • Maltose:

    • Contains two glucose units; formed during starch breakdown.

Polysaccharides and Their Functions

  • Major Types:

    • Glycogen: Stored in muscles and liver; serves as energy reserve.

    • Starch: Plant-derived energy storage; major carbohydrate in diet.

    • Fibers: Indigestible components of plant cell walls; beneficial for digestion and health.

Fiber Types and Their Health Effects

  • Soluble Fibers:

    • Dissolve in water; help lower cholesterol and glucose absorption.

    • Sources: oats, fruits, legumes.

  • Insoluble Fibers:

    • Do not dissolve; promote fecal bulk and help prevent constipation.

    • Sources: whole grains, vegetables.

Digestion and Absorption of Carbohydrates

  • Process Overview:

    • Goal is to break down carbohydrates into monosaccharides for absorption.

  • Digestive Pathway:

    1. Saliva in the mouth begins breakdown with enzymes.

    2. Stomach halts carbohydrate digestion.

    3. Pancreas releases enzymes in the small intestine to further digest carbs.

    4. Monosaccharides absorbed by intestinal cells.

  • Fiber:

    • Not digested but beneficially alters nutrient absorption and digestion speeds.

Blood Glucose Regulation

  • Insulin and Glucagon:

    • Hormones that maintain blood sugar levels; insulin lowers and glucagon raises blood glucose.

Health Effects of Sugars

  • Obesity and Heart Disease:

    • High added sugar intake linked to obesity and lipid buildup in arteries.

  • Dental Health:

    • Sugars promote cavity-causing bacterial growth.

Recommendations for Sugar Intake

  • Moderation is Key:

    • Limit added sugars to less than 10% of total caloric intake; ideally less than 5%.

Alternative Sweeteners

  • Sugar Alcohols:

    • Provide fewer calories than sugars; beneficial in sugar-free foods.

  • Nonnutritive Sweeteners:

    • Provide sweetness without calories; some concerns exist regarding long-term health effects.

Dietary Fiber Recommendations

  • Increase Fiber Intake:

    • Promote whole grains, legumes, fruits, and vegetables for overall health.

  • Limit Excessive Fiber:

    • Can interfere with nutrient absorption and create digestive issues.

Glycemic Index

  • Definition:

    • Measures absorption speed of carbohydrates; informs dietary choices for blood sugar management.

  • Considerations:

    • Low-GI foods may reduce chronic disease risk; however, more research is warranted.

Conclusion

  • Balanced Diet:

    • Carbohydrates should comprise 45-65% of daily caloric intake; focus on healthy sources.

  • Food Sources:

    • Include grains, fruits, vegetables, and legumes to ensure adequate carbohydrate and fiber intake for health benefits.