Carbohydrates: Plant-Derived Energy Nutrients

What Are Carbohydrates?

Carbohydrates are organic molecules composed primarily of carbon, hydrogen, and oxygen, typically in a 1:2:1 ratio. They are the body's primary source of energy and are mostly derived from plants.

• General Formula: Carbohydrates often follow the formula CnH2nOn (e.g., C6H12O6 for glucose).

• Saccharides: The basic units of carbohydrates are saccharides (sugars).

• Primary Energy Source: Carbohydrates are the main fuel for most bodily functions.

Example: Glucose (C6H12O6) is the most biologically important carbohydrate.

Types of Carbohydrates

Carbohydrates are classified as simple or complex based on their structure and function.

• Simple Carbohydrates:

  • Monosaccharides: Single sugar units. Examples: Glucose (primary energy source, stored as glycogen), Fructose (fruit sugar), Galactose (part of lactose).

  • Disaccharides: Two sugar units. Examples:

    • Sucrose: Glucose + Fructose

    • Lactose: Glucose + Galactose

    • Maltose: Glucose + Glucose

  • Lactase: Enzyme that breaks lactose into glucose and galactose.

• Complex Carbohydrates:

  • Polysaccharides: Many sugar units. Examples:

    • Starch: Plant storage form of glucose (includes amylose and amylopectin).

    • Glycogen: Animal storage form (not a major dietary source).

    • Fiber: Non-digestible carbohydrate.

Fiber

Fiber is a type of complex carbohydrate that is not digested by human enzymes.

• Dietary Fiber: Naturally present in foods.

• Functional Fiber: Added to foods for health benefits.

• Soluble Fiber: Dissolves in water, forms gels, slows digestion, lowers cholesterol. Examples: Oats, apples.

• Insoluble Fiber: Does not dissolve, adds bulk to stool, prevents constipation. Examples: Whole grains, vegetables.

• Digestibility: Humans lack the enzyme to digest fiber.

Why We Need Carbohydrates

Carbohydrates are essential for energy and metabolic functions.

• AMDR: 45–65% of total calories should come from carbohydrates.

• Functions:

  • Primary energy source

  • Prevent ketoacidosis

  • Spare protein for other uses

  • Provide fiber benefits

Glucose & Energy

Glucose is vital for energy, especially for red blood cells and the brain.

• RBCs: Rely exclusively on glucose.

• Brain: Primarily depends on glucose.

• Exercise: High intensity uses more carbohydrates; low intensity uses more fat.

Ketoacidosis

When carbohydrate intake is too low, the body produces ketones, which can lead to dangerous ketoacidosis if excessive.

• Ketoacidosis: Excess ketones lower blood pH, causing health risks.

• Ketosis: Normal metabolic state; not dangerous.

Fats: Essential Energy-Supplying Nutrients

What Are Lipids?

Lipids are hydrophobic molecules that serve as a major energy source and structural component in the body. There are three main types:

• Triglycerides

• Phospholipids

• Sterols

Triglycerides

Triglycerides are the most abundant dietary lipid, consisting of three fatty acids and one glycerol molecule.

• Storage: Stored in adipose tissue.

• Energy: Provide 9 kcal per gram.

Phospholipids

Phospholipids contain two fatty acids and a phosphate group, making them amphipathic. They are key components of cell membranes and act as emulsifiers.

• Not essential: The body can synthesize them.

Sterols

Sterols have a four-ring structure. Cholesterol is the most well-known sterol, found only in animal foods.

• Functions: Precursor to vitamin D, bile, testosterone, and estrogen.

• Health Risk: High LDL cholesterol increases cardiovascular disease risk.

Why We Need Fat

Fats are essential for energy storage, insulation, organ protection, and cellular functions.

• AMDR: 20–35% of total calories should come from fat.

• Functions:

  • Energy storage

  • Insulation

  • Organ protection

  • Cell membrane structure

  • Transport of fat-soluble vitamins (A, D, E, K)

Fatty Acids

Fatty acids are hydrocarbon chains with a carboxyl group (-COOH) at one end.

Saturation

The degree of saturation affects the physical properties and health effects of fats.

• Saturated Fat: No double bonds; solid at room temperature; mostly from animal sources; higher health risk.

• Monounsaturated: One double bond.

• Polyunsaturated: Two or more double bonds.

Trans Fats

Trans fats have hydrogen atoms on opposite sides of the double bond, resulting in a straight structure. They are the most harmful type of fat.

• Health Risk: Increase cardiovascular disease risk.

• Source: Created by hydrogenation; partially hydrogenated oils (PHOs) are banned.

Essential Fatty Acids

Essential fatty acids cannot be synthesized by the body and must be obtained from the diet.

• Omega-6

• Omega-3

• Functions: Important for eicosanoid production and inflammation regulation.

Proteins: Crucial Components of All Body Tissues

What Are Proteins?

Proteins are chains of amino acids joined by peptide bonds. They contain nitrogen and provide 4 kcal per gram.

• Sources: Meat, dairy, legumes, nuts, whole grains.

Amino Acids

There are 20 amino acids, 9 of which are essential. Each amino acid has an amine group, an acid group, and a unique side chain (R group).

Protein Structure

Protein function depends on its structure, which is organized into four levels:

• Primary: Sequence of amino acids.

• Secondary: Alpha helices and beta sheets.

• Tertiary: Three-dimensional shape.

• Quaternary: Multiple polypeptide chains.

Example: Sickle cell anemia results from a mutation in the primary structure.

Denaturation

Denaturation is the loss of protein shape and function due to heat, acid, or mechanical agitation. The primary structure remains intact.

• Example: Boiling an egg denatures its proteins.

Protein Synthesis

Protein synthesis involves two main steps:

• Transcription: DNA is transcribed to mRNA.

• Translation: mRNA is translated into an amino acid chain by ribosomes, which form peptide bonds.

Epigenetics & Nutrigenomics

Epigenetics refers to changes in gene expression without altering DNA. Nutrigenomics studies how diet affects gene expression.

Why We Need Protein

Proteins serve many vital functions in the body.

• AMDR: 10–35% of total calories should come from protein.

• Functions:

  • Enzymes

  • Hormones

  • Antibodies

  • Structural support (e.g., collagen)

  • Muscle contraction

  • Fluid balance

  • Acid-base balance

  • Backup energy source

Deamination

Deamination is the removal of the amine group from amino acids, resulting in nitrogen excretion as urea and the use of the remaining carbon skeleton for energy, glucose, or fat.

• Protein: Used as an energy source only as a last resort.

Protein Digestion

Protein digestion occurs in the stomach and small intestine.

• Stomach: HCl denatures proteins; pepsin breaks them down.

• Small Intestine: Proteases further digest proteins to amino acids, which are absorbed into the bloodstream.

Most Tested Concepts

• AMDR ranges: Carbs (45–65%), Fat (20–35%), Protein (10–35%)

• Ketoacidosis vs ketosis: Know the difference and health implications.

• Fiber types: Soluble vs insoluble, dietary vs functional.

• Saturated vs unsaturated fats: Health risks and sources.

• Trans fats: Structure, sources, and health risks.

• Essential fatty acids: Omega-3 and Omega-6 functions.

• Cholesterol functions: Precursor roles and health risks.

• Protein structure levels: Primary to quaternary.

• Denaturation: Causes and effects.

• Deamination: Process and significance.

• RBC uses only glucose: Importance for energy.

• Energy values: Fat = 9 kcal/g, Protein/Carb = 4 kcal/g

Energy Values Table

AMDR Table

Key Chemical Formulas

• Glucose:

• Sucrose:

Summary Table: Types of Carbohydrates

Summary Table: Types of Fats

Summary Table: Protein Structure Levels