Carbohydrates: Mono, Di, and Polysaccharides

• Carbohydrates are organic compounds containing carbon, hydrogen, and oxygen, with a basic formula of (CH2O)n, where n is the number of carbon atoms
• They are a major source of energy for the body
• Carbohydrates are classified into monosaccharides, disaccharides, and polysaccharides, based on the number of sugar units

Monosaccharides

• Monosaccharides are the simplest form of carbohydrates, also known as simple sugars
• Examples include glucose, fructose, and galactose
• Glucose is the primary source of energy for cells
• Fructose is found in fruits and honey and is the sweetest monosaccharide
• Galactose is a component of lactose, or milk sugar

Disaccharides

• Disaccharides are formed when two monosaccharides are joined together by a glycosidic bond
• Common examples include sucrose, lactose, and maltose
• Sucrose (table sugar) is composed of glucose and fructose
• Lactose (milk sugar) is composed of glucose and galactose
• Maltose is composed of two glucose molecules

Polysaccharides

• Polysaccharides are complex carbohydrates made up of many monosaccharide units linked together
• Starch, glycogen, and cellulose are important polysaccharides
• Starch is the primary storage form of glucose in plants
  • It consists of amylose (linear chains) and amylopectin (branched chains)
• Glycogen is the storage form of glucose in animals, found mainly in the liver and muscles
• Cellulose is a structural component of plant cell walls and is a form of dietary fiber

Functions of Carbohydrates

• Providing energy is a key function
  • Glucose is metabolized through glycolysis, the Krebs cycle, and oxidative phosphorylation to produce ATP
• Carbohydrates also act as an energy reserve
  • Glycogen is stored in the liver and muscles for later use
• Carbohydrates are structural components of cells
  • For example, cellulose in plant cell walls and glycoproteins in animal cell membranes
• They are precursors for other biomolecules
  • Carbohydrates can be converted into amino acids and fats
• They are important for digestion
  • Fiber promotes healthy bowel movements and helps regulate blood sugar levels

Digestion and Absorption

• Carbohydrate digestion begins in the mouth with salivary amylase breaking down starch into smaller polysaccharides
• In the small intestine, pancreatic amylase continues to break down starch into disaccharides
• Enzymes like maltase, sucrase, and lactase break down disaccharides into monosaccharides
• Monosaccharides are absorbed into the bloodstream through the intestinal cells
• Glucose is transported to cells throughout the body for energy
• Excess glucose is stored as glycogen in the liver and muscles, or converted into fat

Dietary Recommendations

• The recommended daily intake of carbohydrates is about 45-65% of total daily calories
• Emphasis should be placed on consuming complex carbohydrates like whole grains, fruits, and vegetables
• Intake of added sugars should be limited to less than 10% of total daily calories
• Fiber intake should be around 25-30 grams per day

Health Implications

• Carbohydrates affect blood sugar levels
  • Simple carbohydrates can cause rapid spikes in blood sugar
  • Complex carbohydrates are digested more slowly, resulting in a more gradual increase in blood sugar
• High intake of added sugars is associated with weight gain, type 2 diabetes, and heart disease
• Adequate fiber intake helps prevent constipation, lowers cholesterol levels, and reduces the risk of chronic diseases
• Low-carbohydrate diets can lead to ketosis, where the body relies on fat for energy

Carbohydrate Metabolism

• Glucose metabolism involves several key pathways
  • Glycolysis breaks down glucose into pyruvate
  • The Krebs cycle (citric acid cycle) oxidizes pyruvate to produce energy carriers
  • Oxidative phosphorylation uses these carriers to produce ATP
• Glycogenesis is the synthesis of glycogen from glucose
• Glycogenolysis is the breakdown of glycogen into glucose
• Gluconeogenesis is the synthesis of glucose from non-carbohydrate sources
• Insulin and glucagon are key hormones regulating glucose metabolism
  • Insulin promotes glucose uptake and storage
  • Glucagon promotes glycogen breakdown and glucose release

Carbohydrates and Exercise

• Carbohydrates are a crucial fuel source during exercise
• Muscle glycogen is the primary fuel for moderate to high-intensity exercise
• During prolonged exercise, glycogen stores can be depleted, leading to fatigue
• Consuming carbohydrates during exercise helps maintain blood glucose levels and delay fatigue
• Carbohydrate loading, increasing carbohydrate intake before endurance events, can enhance glycogen stores and improve performance
• Post-exercise carbohydrate consumption helps replenish glycogen stores and promote recovery

Types of Dietary Fiber

• Dietary fiber is classified into soluble and insoluble fiber
• Soluble fiber dissolves in water and forms a gel-like substance in the digestive tract
  • It helps lower cholesterol levels and regulate blood sugar levels
  • Sources include oats, beans, and fruits
• Insoluble fiber does not dissolve in water and adds bulk to the stool
  • It promotes regular bowel movements and prevents constipation
  • Sources include whole grains, vegetables, and wheat bran

Glycemic Index and Glycemic Load

• The glycemic index (GI) measures how quickly a food raises blood glucose levels compared to pure glucose
  • High GI foods cause a rapid increase in blood glucose
  • Low GI foods cause a slower, more gradual increase
• The glycemic load (GL) takes into account both the GI and the amount of carbohydrate in a serving of food
  • GL provides a more accurate measure of a food's impact on blood glucose
• Foods with a low GI and GL are generally preferred for better blood sugar control

Alternative Sweeteners

• Alternative sweeteners are used as sugar substitutes
• Examples include artificial sweeteners and natural sweeteners
• Artificial sweeteners are synthetic compounds that provide sweetness without calories
  • Common ones include aspartame, saccharin, and sucralose
• Natural sweeteners are derived from natural sources but are processed
  • Examples include stevia and erythritol
• These sweeteners can be useful for people with diabetes or those trying to reduce their sugar intake
• They can have different effects on blood sugar and gut health compared to traditional sugars