Carbohydrates: Sugars, Starches, and Fiber

Carbohydrates in the Modern Diet

• Basis of Modern Diets: Carbohydrates make up more than half of the calories consumed by Americans.
• Energy Source: Provide a readily available source of energy with 4 kcal per gram.
• Nutrient Variety: Whole food sources of carbohydrates are rich in essential nutrients needed for health.

Sources of Carbohydrates

• Various food items provide carbohydrates, ranging from oils to fruits and vegetables. Examples include:
• Fruits: Orange, Kiwi, Banana
• Vegetables: Carrot, Broccoli, Potato, Corn
• Grains: Oatmeal, Spaghetti, Whole-wheat bread
• Legumes/Nuts: Kidney beans, Walnuts, Peanut butter
• These foods differ in carbohydrate content and nutritional value.

Whole versus Refined Carbohydrates

• Whole Grains: Contain bran, germ, and endosperm, providing more nutrients (fiber, vitamins).
• Refined Grains: Often stripped of nutritious parts, may be enriched but lack many nutrients found in whole grains.
• Nutritional Trade-off: Refined grains may miss out on magnesium, vitamin E, and B vitamins.

Types of Carbohydrates

1. Simple Carbohydrates:

• Monosaccharides: Single sugar units (e.g., Glucose, Fructose, Galactose).
• Disaccharides: Two sugar units linked together (e.g., Sucrose).

1. Complex Carbohydrates:

• Oligosaccharides: Chains of 3-10 monosaccharides.
• Polysaccharides: Long chains, includes starch and fiber in plants, and glycogen in animals.

Monosaccharides and Their Importance

• Common Monosaccharides: Glucose (blood sugar), Fructose (fruit sugar), Galactose.
• Glucose: Most important fuel for body cells, sourced from diet and synthesized in the body.

Fiber and Its Types

• Dietary Fiber: Cannot be digested; important for digestive health.

1. Soluble Fiber: Dissolves in water; helps lower cholesterol and glucose levels.
2. Insoluble Fiber: Does not dissolve; aids in preventing constipation.

• Recommended Fiber Intake: 25g/day for women, 38g/day for men.

Carbohydrate Digestion and Absorption

• Mouth: Salivary amylase breaks starch into shorter polysaccharides.
• Stomach: No carbohydrate digestion occurs due to acidic environment.
• Small Intestine: Pancreatic amylase breaks starch further into disaccharides and oligosaccharides, which are then converted into monosaccharides for absorption.
• Large Intestine: Fiber is broken down partially by bacteria; the remainder is excreted.

Lactose Intolerance

• Caused by insufficient lactase enzyme; leads to symptoms like bloating, cramping, and diarrhea when consuming dairy products.
• Prevalence varies by ethnicity; higher rates in certain populations (e.g., Native Alaskans, African Americans).

Blood Glucose Regulation

• Body maintains blood glucose levels through insulin and glucagon secretion.
• Insulin: Lowers blood glucose after meals; promotes glucose uptake in cells.
• Glucagon: Raises blood glucose during fasting; stimulates glycogen breakdown and gluconeogenesis.

Cellular Respiration

• Purpose: Glucose metabolized to produce ATP.
• Process: 1 glucose + 6 O₂ → 6 CO₂ + 6 H₂O + 38 ATP.
• Requires oxygen; also known as aerobic metabolism.

Diabetes Overview

• Types:

1. Type 1: Insulin not produced.
2. Type 2: Insulin present but cells are resistant.

• Symptoms and Complications: Excessive thirst/urination, long-term risks include heart disease, kidney failure, nerve damage.

Dietary Carbohydrates and Health

• Whole grains can lower the risk of heart disease; high fiber intake is associated with a lower incidence of colon cancer.
• Nonnutritive Sweeteners: Alternatives like aspartame and sucralose provide sweetness without calories but require safety evaluations.

Nutritional Labeling on Carbohydrates

• Labels typically show total carbohydrates, fiber content, and sometimes distinguish between naturally occurring sugars and added sugars.
• Recent proposals for clearer labeling of added sugars can help consumers make informed choices about carbohydrate intake.