Carbohydrates Overview

Overview

This lecture explains the types, sources, digestion, and dietary recommendations for carbohydrates, including simple sugars, starches, and fibers.

Simple sugars (monosaccharides and disaccharides) are small ring-shaped molecules made of carbon, hydrogen, and oxygen.
Monosaccharides include glucose (main energy source), fructose (in fruits, honey), and galactose (in milk).
Disaccharides are two linked monosaccharides: sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose).
Oligosaccharides are short chains (3-9 sugars), e.g., galacto-oligosaccharides in soybeans.
Polysaccharides are long chains (10+ sugars), e.g., starches and dietary fibers.

Sugars are found naturally in plants (fruits, vegetables, grains) and animal products (milk, cheese).
Added sugars are put into foods during processing, regardless of their source (e.g., honey, cane sugar).
Carbohydrates provide calories and energy, sweeten foods, help preservation, and support fermentation.

Enzymes like amylase, maltase, sucrase, and lactase break down polysaccharides and disaccharides into monosaccharides.
Monosaccharides are absorbed into the bloodstream for energy or storage.
Insulin helps glucose enter cells and promotes storage as glycogen in the liver.
Galactose is converted to glucose in the liver; fructose is mostly broken down to enter glycolysis.

Dietary fibers are polysaccharides indigestible by human enzymes but partially broken down by gut bacteria.
Fiber slows glucose absorption, helps prevent constipation, and supports heart health.
Fibers increase stool weight and promote regular bowel movements.

45-65% of total calories should come from carbohydrates.
About 28g of fiber per 2000-calorie diet is recommended.
Added sugars should be less than 10% of total calories (World Health Organization and US guidelines).
Choose nutrient-rich carbohydrate sources (fruits, vegetables, dairy, grains) and limit added sugars.

Monosaccharide — single sugar molecule (e.g., glucose, fructose, galactose).
Disaccharide — two monosaccharide molecules linked together (e.g., sucrose, lactose, maltose).
Oligosaccharide — carbohydrate with 3-9 linked monosaccharide units.
Polysaccharide — carbohydrate with 10 or more linked monosaccharide units (e.g., starch, fiber).
Glycosidic bond — chemical bond linking monosaccharides in carbohydrates.
Glycogen — storage polysaccharide of glucose in the liver and muscles.

Review nutrition labels to compare carbohydrate, fiber, and added sugar content.
Aim to meet daily fiber and carbohydrate recommendations with nutrient-rich foods.
Limit added sugar intake to less than 10% of daily calories.