Carbohydrates: Sugars, Starches, and Fibers

Types and Structures of Carbohydrates

Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen. They are classified based on the number of sugar units present.

• Monosaccharides: Single sugar units such as glucose (primary energy source for the body), fructose, and galactose.

• Disaccharides: Two monosaccharides joined by a condensation reaction (releases water). Examples:

  • Sucrose = glucose + fructose

  • Lactose = glucose + galactose

  • Maltose = glucose + glucose

• Oligosaccharides: 3–10 sugar units; found in beans and legumes; often fermented in the colon, causing gas.

• Polysaccharides: Long chains of glucose units. Major types include:

  • Starch: Storage form in plants. Two forms:

    • Amylose: Straight chain; digested more slowly.

    • Amylopectin: Branched; digested more rapidly.

  • Glycogen: Highly branched storage form in animals, stored in liver and muscle.

  • Fiber: Non-digestible carbohydrate; provides health benefits.

Types and Functions of Fiber

• Insoluble Fiber: Adds bulk to stool, prevents constipation, lowers risk of diverticulosis.

• Soluble Fiber: Forms a gel in the digestive tract, lowers LDL cholesterol, slows glucose absorption.

• Health Benefits: Improved bowel regularity, lower cholesterol, improved blood glucose control, reduced risk of heart disease and type 2 diabetes.

Carbohydrate Digestion and Metabolism

• Condensation Reaction: Joins molecules together, releasing water.

• Hydrolysis: Breaks bonds using water.

• Insulin: Lowers blood glucose by moving glucose into cells.

• Glucagon: Raises blood glucose by stimulating glycogen breakdown.

• Gluconeogenesis: Production of glucose from protein or fat when carbohydrate intake is low.

Dietary Recommendations and Indices

• DRI (Dietary Reference Intake): Minimum 130g carbohydrate/day for brain function.

• Fiber: 25g/day for women, 38g/day for men.

• AMDR (Acceptable Macronutrient Distribution Range): 45–65% of total calories from carbohydrates.

• Glycemic Index (GI): Measures how quickly a food raises blood glucose.

• Glycemic Load (GL): GI multiplied by the amount of carbohydrate in a serving.

Diabetes and Blood Glucose Disorders

• Type 1 Diabetes: Autoimmune destruction of pancreatic beta cells; no insulin production.

• Type 2 Diabetes: Insulin resistance and eventual decreased insulin production; associated with obesity and inactivity.

• Prediabetes: Elevated blood glucose not high enough for diabetes diagnosis; reversible with lifestyle changes.

• Gestational Diabetes: Develops during pregnancy; increases risk of type 2 diabetes later in life.

• A1c ≥ 6.5%: Indicates diabetes; reflects 3-month average blood glucose.

• Hypoglycemia: Blood glucose <70 mg/dL; symptoms include shakiness and confusion.

• Hyperglycemia: Fasting blood glucose >125 mg/dL; symptoms include thirst and frequent urination.

• Long-term complications: Neuropathy, nephropathy, retinopathy, cardiovascular disease.

Whole Grains

• Bran: Contains fiber.

• Germ: Contains vitamins and minerals.

• Endosperm: Contains starch.

Fats, Oils, and Other Lipids

Types and Functions of Lipids

• Triglycerides: Three fatty acids attached to a glycerol backbone; main storage form of fat in the body.

• Phospholipids: Contain a phosphate group; major component of cell membranes.

• Sterols: Include cholesterol; important for hormone and vitamin D production.

Fatty Acids: Classification and Health Effects

• Saturated Fatty Acids: No double bonds; solid at room temperature; found in animal fats and tropical oils; raise LDL cholesterol.

• Unsaturated Fatty Acids: One or more double bonds; liquid at room temperature; heart-healthy when replacing saturated fat.

• Monounsaturated Fats: One double bond (e.g., olive oil, avocado); lower LDL cholesterol.

• Polyunsaturated Fats: Multiple double bonds (e.g., omega-3 and omega-6 fatty acids); reduce heart disease risk.

• Essential Fatty Acids: Must be obtained from the diet:

  • Linoleic acid (omega-6)

  • Alpha-linolenic acid (omega-3)

• Hydrogenation: Adds hydrogen to unsaturated fats, making them more solid; creates trans fats which raise LDL and lower HDL cholesterol.

Lipid Transport and Blood Lipids

• Lipoproteins: Transport lipids in the blood.

  • Chylomicrons: Carry dietary fat from intestine to tissues.

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

  • LDL (Low-Density Lipoprotein): Delivers cholesterol to cells; high levels increase heart disease risk.

  • HDL (High-Density Lipoprotein): Removes cholesterol from cells and returns it to the liver; high levels are protective.

• Desirable Blood Lipid Levels:

  • Total cholesterol: <200 mg/dL

  • LDL: <100 mg/dL

  • HDL: >60 mg/dL

• AMDR for Fat: 20–35% of total calories; saturated fat <10%; avoid trans fats.

Heart Disease and Lipids

• Atherosclerosis: Plaque buildup in arteries leading to heart disease.

• Prevention: Healthy fats, high fiber intake, regular exercise.

Proteins and Amino Acids

Structure and Types of Amino Acids

• Proteins: Polymers of amino acids linked by peptide bonds; contain carbon, hydrogen, oxygen, and nitrogen.

• 20 amino acids: 9 essential (must be obtained from diet), 11 nonessential (can be synthesized by the body).

• Conditionally essential amino acids: Required in greater amounts during illness or stress.

Protein Structure and Function

• Primary structure: Sequence of amino acids.

• Secondary structure: Alpha helix or beta sheet formation.

• Tertiary structure: 3D folding of the polypeptide.

• Quaternary structure: Multiple polypeptide chains combined.

• Denaturation: Loss of protein shape due to heat, acid, or agitation.

Protein Metabolism

• Deamination: Removal of nitrogen from amino acids.

• Transamination: Transfer of nitrogen to form new amino acids.

• Nitrogen balance: Positive (growth, pregnancy), negative (illness, starvation).

Protein Quality and Dietary Sources

• Complete proteins: Contain all essential amino acids (animal sources, soy dairy)).

• Incomplete proteins: Lack one or more essential amino acids (most plant sources).

• Complementary proteins: Combining plant proteins to provide all essential amino acids (e.g., beans + rice).

• PDCAAS (Protein Digestibility Corrected Amino Acid Score): Measures protein quality based on amino acid content and digestibility.

Protein-Energy Malnutrition (PEM)

• Marasmus: Severe wasting due to deficiency of protein and calories.

• Kwashiorkor: Edema and fatty liver due to protein deficiency with adequate energy intake.

Alcohol

Alcohol Structure and Metabolism

• Ethanol (C2H5OH): Provides 7 kcal/gram; not an essential nutrient.

• Standard drink: 12 oz beer, 5 oz wine, 1.5 oz distilled spirits.

• Absorption: Occurs in the stomach and small intestine; metabolized mainly in the liver.

• Metabolic Pathways:

  • Alcohol dehydrogenase: Converts ethanol to acetaldehyde.

  • Acetaldehyde dehydrogenase: Converts acetaldehyde to acetate.

  • MEOS (Microsomal Ethanol Oxidizing System): Used in heavy drinking.

Blood Alcohol Concentration (BAC) and Effects

• BAC: Percentage of alcohol in the blood; women typically have higher BAC than men after the same intake.

• Short-term effects: Impaired coordination, slowed reaction time, dehydration.

• Long-term effects: Fatty liver → alcoholic hepatitis → cirrhosis.

• Fetal Alcohol Syndrome: Growth restriction, facial abnormalities, brain damage in infants exposed to alcohol in utero.

Key Equations

• Energy from Alcohol:

Example: A 14g (standard drink) serving of alcohol provides kcal.