Overview
This lecture provides an in-depth examination of carbohydrates, their classifications, chemical structures, and the nutritional significance of different types, including sugars, starches, and fibers.
Carbohydrate Basics
- Carbohydrates are organic compounds with a 1:2:1 ratio of carbon, hydrogen, and oxygen atoms.
- Their main function is to provide energy to cells, especially the brain and nervous system.
- The basic unit of carbohydrates is the monosaccharide (single sugar molecule).
Classification of Carbohydrates
- Carbohydrates are divided into fast-releasing (sugars) and slow-releasing (starches and fibers) types.
- Fast-releasing carbohydrates include monosaccharides and disaccharides.
- Slow-releasing carbohydrates are polysaccharides, which are long chains of sugar units.
Fast-Releasing Carbohydrates
- Monosaccharides include glucose (primary energy source), galactose (converted to glucose), and fructose (found in fruit).
- Sugar alcohols (like xylitol) are modified sugars that provide fewer calories and do not cause tooth decay.
- Disaccharides are composed of two monosaccharides, such as sucrose (table sugar), lactose (milk sugar), and maltose.
Slow-Releasing Carbohydrates
- Polysaccharides include starches (amylose and amylopectin) found in plants and glycogen found in animals.
- Cooking makes plant starches more digestible; some remain as resistant starch, aiding gastrointestinal health.
- Glycogen is the energy storage form of glucose in liver and muscle tissues.
Dietary Fibers
- Dietary fibers are complex polysaccharides that cannot be digested by human enzymes but are partly broken down by gut bacteria.
- Soluble fibers (like pectin) dissolve in water and are found in oats, beans, and barley; insoluble fibers (like cellulose) are found in whole grains and vegetables.
- Functional fibers are added to foods for health benefits, such as lowering blood cholesterol.
Key Terms & Definitions
- Monosaccharide — Simple sugar molecule (e.g., glucose, fructose, galactose).
- Disaccharide — A carbohydrate made of two monosaccharide units (e.g., sucrose, lactose).
- Polysaccharide — Long-chain carbohydrate made of many monosaccharides (e.g., starch, fiber).
- Sugar alcohol — Modified carbohydrate with fewer calories, used as a sweetener.
- Starch — Energy-storing polysaccharide in plants.
- Glycogen — Storage form of glucose in animals.
- Dietary fiber — Indigestible plant polysaccharide promoting health benefits.
- Functional fiber — Added fibers in foods with proven health effects.
Action Items / Next Steps
- Reflect on whether your diet is higher in sugars, starches, or fibers.
- Bring bread packaging to class and compare ingredient lists for whole grain content and added sugars.
- Visit the Whole Grains Council website to learn how to identify whole grain products.