Carbohydrates: Structure, Function, and Health Implications

Classification and Nomenclature of Carbohydrates (CHO)

• Monosaccharides: The simplest carbohydrates, consisting of a single sugar unit. Examples include glucose, fructose, and galactose.

• Disaccharides: Composed of two monosaccharide units. Examples: sucrose (glucose + fructose), lactose (glucose + galactose), maltose (glucose + glucose).

• Oligosaccharides: Chains of 3–10 monosaccharide units. Found in foods like beans and legumes; often not fully digestible, contributing to gas production.

• Polysaccharides: Long chains of monosaccharide units. Includes starches (amylose, amylopectin), glycogen (animal storage form), and fibers (cellulose, hemicellulose, pectin).

Starches

• Amylose: Linear chain of glucose units.

• Amylopectin: Branched chain of glucose units; more easily digested.

Glycogen

• The storage form of glucose in animals, highly branched for rapid mobilization.

Dietary Fiber

• Insoluble Fiber: Does not dissolve in water; promotes bowel regularity (e.g., cellulose, some hemicelluloses).

• Soluble Fiber: Dissolves in water to form gels; can lower blood cholesterol and glucose (e.g., pectin, gums).

• Health Benefits: Reduces risk of heart disease, improves digestive health, aids in weight management.

Chemical Reactions

• Condensation: Formation of a bond between two molecules with the release of water (e.g., forming disaccharides).

• Hydrolysis: Breaking a bond by adding water (e.g., digestion of polysaccharides).

Dietary Recommendations

• DRI for Carbohydrates: 130 g/day minimum for adults.

• AMDR for Carbohydrates: 45–65% of total daily calories.

• Fiber: 25 g/day for women, 38 g/day for men (varies by age).

Digestion and Absorption

• Begins in the mouth (salivary amylase), continues in the small intestine (pancreatic amylase).

• Monosaccharides absorbed into the bloodstream via the small intestine.

Lactose Intolerance

• Inability to digest lactose due to low lactase enzyme; leads to GI symptoms after dairy consumption.

Blood Glucose Regulation

• Insulin: Lowers blood glucose by promoting uptake into cells.

• Glucagon: Raises blood glucose by stimulating glycogen breakdown.

• Other Hormones: Epinephrine, cortisol, and growth hormone can also raise/maintain blood glucose.

Diabetes Mellitus

• Type 1: Autoimmune destruction of pancreatic beta cells; requires insulin therapy.

• Type 2: Insulin resistance; often associated with obesity.

• Prediabetes: Elevated blood glucose, not yet diabetic.

• Gestational Diabetes: Develops during pregnancy.

• Symptoms: Polyuria, polydipsia, polyphagia, unexplained weight loss (Type 1).

• A1c: Glycated hemoglobin; reflects average blood glucose over 2–3 months.

• Long-term Complications: Cardiovascular disease, neuropathy, nephropathy, retinopathy.

• Prevention: Healthy diet, physical activity, weight management.

Ketones

• Produced during fat breakdown when carbohydrate is insufficient; can lead to ketosis.

Added Sugars and Sugar Substitutes

• Added Sugars: Sugars added during processing (e.g., sucrose, HFCS).

• High Fructose Corn Syrup (HFCS): Common sweetener in processed foods.

• Sugar Substitutes: Non-nutritive sweeteners (e.g., aspartame, sucralose).

Dietary Fiber and Cholesterol

• Soluble fiber can lower LDL cholesterol by binding bile acids in the intestine.

Whole Grains and High-Fiber Foods

• Examples: Oats, brown rice, whole wheat, barley, legumes, fruits, and vegetables.

Diverticulosis and Diverticulitis

• Diverticulosis: Formation of pouches in the colon wall.

• Diverticulitis: Inflammation/infection of these pouches.

Glycemic Index and Glycemic Load

• Glycemic Index (GI): Ranks foods by their effect on blood glucose.

• Glycemic Load (GL): GI adjusted for serving size. Formula:

Lipids: Structure, Function, and Health

Lipid Classifications and Functions

• Triglycerides (TG): Main form of dietary and stored fat; composed of glycerol + 3 fatty acids.

• Phospholipids (PL): Major component of cell membranes; amphipathic structure.

• Sterols: Includes cholesterol; precursor for steroid hormones, vitamin D, bile acids.

• Phytosterols & Stanols: Plant sterols that can lower cholesterol absorption.

Fatty Acids: Types and Characteristics

• Saturated Fatty Acids (SFA): No double bonds; solid at room temperature (e.g., butter, lard).

• Unsaturated Fatty Acids (UFA): One or more double bonds; liquid at room temperature.

• Monounsaturated Fatty Acids (MUFA): One double bond (e.g., olive oil).

• Polyunsaturated Fatty Acids (PUFA): Two or more double bonds (e.g., corn oil, fish oil).

• Omega-3 (α-linolenic acid) and Omega-6 (linoleic acid): Essential fatty acids; must be obtained from diet.

Digestion and Absorption of Lipids

• Emulsification by bile in the small intestine forms micelles for absorption.

• Lipases break down triglycerides into fatty acids and monoglycerides.

Lipoproteins

• Chylomicrons: Transport dietary lipids from intestine to tissues.

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

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

• HDL (High Density Lipoprotein): Removes cholesterol from cells; protective against heart disease.

Dietary Recommendations

• AMDR for Fat: 20–35% of total calories.

• Saturated Fat: Less than 10% of calories.

• Trans Fat: As low as possible.

• Linoleic Acid (Omega-6): 17 g/day (men), 12 g/day (women).

• Alpha-linolenic Acid (Omega-3): 1.6 g/day (men), 1.1 g/day (women).

Heart Disease and Lipids

• High LDL and low HDL increase risk.

• Prevention: Limit saturated/trans fats, increase fiber, exercise, maintain healthy weight.

• Desirable blood lipid levels:

  • Total cholesterol (TC): <200 mg/dL

  • LDL: <100 mg/dL

  • HDL: >60 mg/dL

Hydrogenation

• Process of adding hydrogen to unsaturated fats to make them more solid; creates trans fats.

Rancidity

• Oxidative spoilage of fats, especially PUFAs; antioxidants can delay rancidity.

Proteins: Structure, Function, and Nutrition

Protein Structure and Building Blocks

• Amino Acids: 20 total; 9 essential (must be obtained from diet), 11 non-essential (can be synthesized).

• Conditionally Essential: Required in diet under certain conditions (e.g., illness).

• Peptide Bonds: Link amino acids together to form peptides and proteins.

• Protein Structure:

  • Primary: Sequence of amino acids

  • Secondary: Alpha helices and beta sheets

  • Tertiary: 3D folding

  • Quaternary: Multiple polypeptide chains

Protein Digestion and Absorption

• Begins in the stomach (pepsin), continues in the small intestine (proteases).

• Amino acids absorbed into the bloodstream via the small intestine.

Protein Synthesis

• Transcription: DNA to mRNA in the nucleus.

• Translation: mRNA to protein at the ribosome.

• Elongation: Addition of amino acids to the growing chain.

• Sequencing Errors: Can result in nonfunctional proteins (e.g., sickle cell anemia).

Protein Functions

• Structural (muscle, skin, hair), enzymes, hormones, immune function, fluid balance (albumin), transporters.

Protein Needs and Nitrogen Balance

• RDA: 0.8 g/kg body weight for adults.

• Nitrogen Balance: Intake vs. loss; positive (growth), negative (illness), equilibrium (healthy adult).

• Calculation: where UUN = urinary urea nitrogen

Protein Quality

• Complete Proteins: Contain all essential amino acids (e.g., animal proteins, soy).

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

• Amino Acid Score, PDCAAS: Methods to evaluate protein quality.

Protein-Energy Malnutrition (PEM)

• Marasmus: Severe energy and protein deficiency; wasting.

• Kwashiorkor: Protein deficiency with adequate energy; edema, fatty liver.

Vegetarian Diets

• Types: Lacto-ovo, lacto, ovo, vegan, pescatarian.

• Benefits: Lower risk of heart disease, hypertension, type 2 diabetes.

• Risks: Potential deficiencies in vitamin B12, iron, zinc, omega-3s.

Alcohol: Metabolism and Health Effects

Alcohol Structure and Standard Drink

• Alcohol (Ethanol): 2-carbon compound; psychoactive substance.

• Standard Drink: 14 g pure alcohol (e.g., 12 oz beer, 5 oz wine, 1.5 oz spirits).

Dietary Guidelines

• Moderation: Up to 1 drink/day for women, 2 for men.

Absorption, Circulation, and Metabolism

• Absorbed in stomach and small intestine; no digestion required.

• Metabolized primarily in the liver via:

  • Alcohol dehydrogenase (ADH)

  • Acetaldehyde dehydrogenase

  • MEOS (Microsomal Ethanol-Oxidizing System)

Blood Alcohol Concentration (BAC)

• Expressed as %; affected by sex, genetics, body composition.

Short- and Long-Term Effects

• Short-term: Impaired judgment, coordination, risk of accidents.

• Long-term: Liver disease (fatty liver, alcoholic hepatitis, cirrhosis), brain damage, increased cancer risk.

Alcohol Use Disorders

• Alcoholism: Chronic dependence on alcohol.

• Alcohol Abuse: Harmful use without dependence.

Fetal Alcohol Syndrome

• Caused by alcohol exposure during pregnancy; leads to birth defects and developmental disorders.

Water: Balance, Regulation, and Health

Water and Electrolyte Balance

• Na-K Pump: Maintains sodium and potassium gradients across cell membranes; essential for nerve and muscle function.

Water and Blood Pressure Regulation

• Hormones:

  • ADH (Vasopressin): Promotes water reabsorption in kidneys.

  • Angiotensin II: Stimulates vasoconstriction and aldosterone release.

  • Aldosterone: Increases sodium and water retention.

• Enzyme: Renin: Initiates the renin-angiotensin-aldosterone system (RAAS).

• Organs: Brain (hypothalamus), kidneys, liver, lungs all play roles in water and BP regulation.

Water Recommendations

• Men: ~3.7 L/day; Women: ~2.7 L/day (from all beverages and foods).

• Needs vary with physical activity, diet, environment.

Sources of Water

• Drinking water, beverages, fruits, vegetables.

Caffeine, Alcohol, and Water Balance

• Caffeine: Mild diuretic; increases urine output but not usually dehydrating in moderate amounts.

• Alcohol: Inhibits ADH, leading to increased water loss and risk of dehydration.

• Diuretic: Substance that increases urine production.

Sodium and Potassium

• Key electrolytes for fluid balance, nerve transmission, muscle contraction.

Hyponatremia

• Low blood sodium; can result from excessive water intake or loss of sodium.

Dehydration

• First sign: Thirst.

• Other signs: Dry mouth, fatigue, decreased urine output, confusion.

Monitoring Water Intake

• To avoid dehydration/overhydration: Weigh before and after exercise; consume 16 oz (480 mL) for every pound lost.