ASIN500_Lecture_3_-_Carbohydrates_moodle

Introduction to Carbohydrates

• Carbohydrates play a critical role in nutrition.

Lecture Objectives

• After this lecture, you should be able to:

  • Outline the three major types of carbohydrates: monosaccharides, disaccharides, polysaccharides.

  • Discuss types of fiber: their classification and health benefits.

  • Explain hormonal regulation of blood glucose: understanding how insulin and glucagon work.

  • Discuss the glycemic index (GI): how it's used and factors that affect it.

  • Describe the impact of carbohydrates on health: both positive and negative effects.

Types of Carbohydrates

• Monosaccharides:

  • Glucose, Fructose, Galactose.

• Disaccharides:

  • Sucrose, Lactose, Maltose.

• Polysaccharides:

  • Starch, Cellulose, Glycogen.

Monosaccharides

• Definition: Single sugar units.

  • Glucose:

    • Found in fruits, vegetables, honey.

    • Known as "blood sugar"; primary energy source.

  • Fructose:

    • Found in fruits, honey, corn syrup (HFCS).

    • Known as "fruit sugar".

  • Galactose:

    • Part of lactose in milk.

Disaccharides

• Definition: Two linked sugar units.

  • Sucrose: (glucose + fructose)

    • Commonly known as table sugar from sugar cane/beets.

  • Lactose: (glucose + galactose)

    • Known as milk sugar, found in dairy products.

  • Maltose: (glucose + glucose)

    • Found in germinating grains; product of starch breakdown.

Polysaccharides

• Definition: Many sugar units.

  • Starch:

    • Found in plants as long chains of glucose.

      • Amylose: Straight chains.

      • Amylopectin: Branched chains.

  • Glycogen:

    • Animal storage form of carbohydrate, highly branched chains of glucose; stored in muscle and liver.

Dietary Fiber

• Recommended Intake: 25-30g per day.

• Types of Fiber:

  1. Soluble Fiber:

     • Includes pectins, gums, mucilages; lowers cholesterol and glucose absorption.

     • Found in fruits, oats, barley, legumes.

  2. Insoluble Fiber:

     • Includes lignins, cellulose; increases gut transit time and fullness.

     • Found in vegetables, wheat, grains.

Fiber in Foods

• Grains: Around 1-2g of fiber per serving.

  • Examples: Whole-grain bread, cereals, cooked barley.

• Vegetables: Around 2-3g fiber.

  • Examples: Broccoli, carrots, spinach.

• Fruits: Around 2g fiber.

  • Examples: Apples, bananas, berries.

• Legumes: 6-8g fiber.

  • Examples: Baked beans, lentils, black beans.

Maximizing Fiber Intake

• Aim for 30g or more daily.

• Recommendations by meal:

  • Include whole grains and legumes several times weekly.

• Examples of fiber-rich foods:

  • Chia seeds, wholegrain cereals, fruits (such as pears), legumes (like chickpeas).

Fate of Glucose

• Pathway of Glucose Utilization:

  • Pancreatic islet cells detect glucose.

  • Insulin released to facilitate glucose uptake by fat and muscle cells.

Blood Glucose Disposal

• Skeletal Muscle: Main site for glucose storage and disposal.

Hyperglycemia

• High blood sugar levels linked to:

  • Increased insulin levels.

  • Risks include coronary heart disease (CHD) and other health issues.

Hypoglycemia

• Low blood sugar symptoms include:

  • Lethargy, confusion, anxiety, and shaking.

  • Often due to inadequate carbohydrate intake or high physical activity levels.

• Remedy: Use quick sources of sugars to elevate blood glucose.

Glycemic Index (GI)

• Definition: A ranking of carbohydrate foods (0-100) of how they affect blood sugar levels compared to a standard.

  • High GI Foods: Rapid increase in blood glucose.

  • Low GI Foods: Slower increase and more sustained effect.

Factors Affecting GI

• Type of sugar (glucose vs fructose).

• Starch type (amylose vs amylopectin).

• Cooking methods and processing.

• Presence of fiber.

• Content of fat and protein in food.

• Acidity level in the food.

Carbohydrates in the Diet

• Daily CHO requirements vary by individual factors (e.g., gender, body size).

• Recommended intake: Minimum of 80-100g daily.

• For minimal activity: 2-4g/kg/d is sufficient.

• Prolonged restriction of carbohydrates (<50g/day) may lead to negative side effects.

20g Carbohydrate Portions

• Examples of serving sizes that equal ~20g CHO:

  • ½ cup corn, 1 medium potato, 1 large fruit.

  • 1 slice of thick bread, ½ cup of pasta or rice.

Carbohydrates and Health

• Negative Effects of High Sugar Intake:

  • Tooth decay, obesity, elevated insulin levels, increased risk of cardiovascular diseases (CVD).

• Positive Benefits of High Fiber Intake:

  • Improved blood glucose control, reduced bowel cancer risk, healthier GI tract.

• Recommendations to increase fiber:

  • Incorporating whole grains, fruits, and vegetables into daily diet.

Summary

• Carbohydrates are categorized into monosaccharides, disaccharides, and polysaccharides.

• Understanding carbohydrates' impacts on health, fiber types, and their health benefits is vital.