Carbohydrates

General Chemical Formula

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, typically with the general formula:

• General formula:

Classification of Carbohydrates

• Monosaccharides: Simple sugars such as glucose, galactose, and fructose.

• Disaccharides: Composed of two monosaccharides; examples include lactose, maltose, and sucrose.

• Polysaccharides: Long chains of monosaccharides; examples include starches (amylose/amylopectin), glycogen (animal storage), and fiber (cellulose).

Caloric Content

• Carbohydrates provide:

Glycemic Index

The glycemic index (GI) measures how quickly a carbohydrate-containing food raises blood glucose levels. Foods with a high GI cause rapid increases in blood sugar, while low GI foods result in slower, more gradual increases.

• Reference sugar for GI: Glucose (GI = 100)

• Application: Used to guide dietary choices for blood sugar management.

Fiber

• Definition: Indigestible carbohydrates found in plant foods.

• Role: Aids in digestion, helps regulate cholesterol, and promotes satiety.

• Examples: Whole grains, fruits, vegetables.

Glycogen Storage

• Location: Primarily stored in the liver and skeletal muscles.

• Duration: Glycogen stores can last from several hours to a day, depending on activity and diet.

Digestion and Accessory Organs

Digestive Organs and Their Functions

• Mouth: Mechanical breakdown, salivary amylase begins carbohydrate digestion.

• Stomach: Protein digestion begins, minimal carbohydrate digestion.

• Small Intestine: Major site for digestion and absorption; enzymes break down carbohydrates, proteins, and lipids.

• Liver: Produces bile for fat emulsification.

• Pancreas: Secretes digestive enzymes and insulin.

• Gallbladder: Stores and releases bile.

Digestive Enzymes

• Amylase: Breaks down starches into sugars.

• Lipase: Breaks down lipids into fatty acids and glycerol.

• Protease: Breaks down proteins into amino acids.

Hormonal Regulation of Blood Sugar

Insulin and Glucagon

• Insulin: Secreted by beta cells of the pancreas; lowers blood glucose by promoting uptake into cells.

• Glucagon: Secreted by alpha cells of the pancreas; raises blood glucose by stimulating glycogen breakdown in the liver.

Hormonal Control

• Insulin: Released after meals; promotes storage of glucose as glycogen.

• Glucagon: Released during fasting; promotes release of glucose from glycogen stores.

Diabetes Mellitus

• Type I Diabetes: Autoimmune destruction of beta cells; requires insulin therapy.

• Type II Diabetes: Insulin resistance; often associated with obesity and lifestyle factors.

Carbohydrates vs. Lipids

Metabolic Pathways

• Carbohydrates: Primary energy source; metabolized via glycolysis and the citric acid cycle.

• Lipids: Secondary energy source; metabolized via beta-oxidation.

Preferred Fuel for the Brain

• Glucose: The brain primarily uses glucose for energy.

Lipids

Classification of Lipids

• Saturated vs. Unsaturated: Saturated fats have no double bonds; unsaturated fats have one or more double bonds.

• Trans Fats: Unsaturated fats with trans double bonds; associated with increased cardiovascular risk.

Structural Formulas of Lipids

• Triglycerides:

• Phospholipids:

• Sterols: Four-ring structure (e.g., cholesterol).

Essential vs. Non-Essential Nutrients

• Essential Nutrients: Must be obtained from the diet; the body cannot synthesize them.

• Non-Essential Nutrients: Can be synthesized by the body.

• Examples of Essential Lipids: Linoleic acid (omega-6), alpha-linolenic acid (omega-3).

Cholesterol and Lipoproteins

Role of Cholesterol

• Function: Component of cell membranes, precursor for steroid hormones and vitamin D.

• Energy Content: (for lipids in general)

Lipoproteins

• Chylomicrons: Transport dietary lipids from intestines to tissues.

• VLDL (Very Low-Density Lipoprotein): Transports triglycerides from liver to tissues.

• LDL (Low-Density Lipoprotein): Delivers cholesterol to cells; high levels associated with cardiovascular risk.

• HDL (High-Density Lipoprotein): Removes excess cholesterol from tissues; protective effect.

"Good" vs. "Bad" Cholesterol

• "Good" Cholesterol: HDL

• "Bad" Cholesterol: LDL

Energy Calculation

Calculating Total Energy Content

To calculate the total energy content of a food item, use the following formula:

• Formula:

Summary Table: Lipoproteins and Their Functions

Additional info:

• Some content inferred from standard nutrition curriculum (e.g., details on fiber, essential fatty acids, and lipoprotein functions).

• Table reconstructed for clarity and completeness.