Comprehensive Study Guide: Carbohydrates, Lipids, Proteins, Enzymes, Vitamins, and Minerals

Carbohydrates

Definition and Sources

Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen, primarily serving as the body's main source of energy. They are found in foods such as grains, fruits, vegetables, legumes, and dairy products.

• Definition: Carbohydrates are sugars, starches, and fibers present in food.

• Sources: Plants (via photosynthesis), dairy products, and processed foods.

Functions of Carbohydrates

• Primary energy source for the brain and muscles during exercise.

• Protein sparing: Prevents the use of protein for energy.

• Promotes digestive health through dietary fiber.

Monosaccharides

• Definition: The simplest form of carbohydrates, consisting of a single sugar unit.

• Types:

  • Glucose: Main energy source for cells.

  • Fructose: Found in fruits and honey; sweetest natural sugar.

  • Galactose: Part of lactose in milk.

• Corn syrup and high fructose corn syrup: Sweeteners derived from corn starch; high fructose corn syrup contains more fructose and is linked to increased risk of obesity and metabolic diseases.

Disaccharides

• Definition: Carbohydrates composed of two monosaccharide units.

• Types and Composition:

  • Sucrose: Glucose + Fructose (table sugar)

  • Lactose: Glucose + Galactose (milk sugar)

  • Maltose: Glucose + Glucose (product of starch digestion)

• Lactose intolerance: Caused by lactase deficiency; symptoms include bloating, gas, and diarrhea after consuming dairy.

• Added sugars: Sugars added during processing; excessive intake linked to chronic diseases.

• Alternative sweeteners: Non-nutritive or low-calorie sweeteners (e.g., aspartame, sucralose). Aspartame is unsafe for individuals with PKU (phenylketonuria).

Polysaccharides

• Definition: Complex carbohydrates made of many monosaccharide units.

• Types:

  • Starch: Storage form in plants; digestible by humans.

  • Glycogen: Storage form in animals; stored in liver and muscles.

  • Fiber: Indigestible plant material; promotes gut health.

• Glycogen storage: Stored in liver (regulates blood glucose) and muscles (energy for activity); released via glycogenolysis when energy is needed.

• Fiber:

  • Function: Promotes bowel regularity, lowers cholesterol, controls blood glucose.

  • Types: Soluble (dissolves in water, e.g., oats) and insoluble (adds bulk, e.g., wheat bran).

  • Benefits: Reduces risk of heart disease, diabetes, and certain cancers.

Carbohydrate Digestion, Absorption, and Transport

• Digestion Pathway: Begins in mouth (salivary amylase), continues in small intestine (pancreatic amylase, brush border enzymes).

• Enzymes: Amylase (saliva, pancreas), maltase, sucrase, lactase (small intestine).

• Absorption: Occurs in small intestine; monosaccharides absorbed into bloodstream.

• Transport: Glucose transported to liver via portal vein.

Regulating Blood Glucose Levels

• Hormones: Insulin (lowers blood glucose), glucagon (raises blood glucose).

• Secretion: Both secreted by pancreas; insulin from beta cells, glucagon from alpha cells.

• Diabetes:

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

  • Type 2: Insulin resistance; managed with diet, exercise, medication.

  • Gestational: Occurs during pregnancy.

  • Testing: Fasting blood glucose, oral glucose tolerance, HbA1c (glycated hemoglobin; reflects average glucose over 2-3 months).

  • Normal range: Fasting glucose 70-99 mg/dL; HbA1c < 5.7%.

  • Glycemic index: Ranks foods by effect on blood glucose; used to manage diabetes.

Lipids

Functions of Fats in the Body

• Energy storage and supply

• Insulation and protection of organs

• Component of cell membranes

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

Triglycerides

• Definition: Main form of fat in food and body; composed of glycerol and three fatty acids.

Saturated vs Unsaturated Fats

• Saturated fats: No double bonds; solid at room temperature; found in animal fats, butter.

• Unsaturated fats: One or more double bonds; liquid at room temperature; found in plant oils, nuts, fish.

Unsaturated Fats

• Essential: Omega-3 (alpha-linolenic acid), Omega-6 (linoleic acid)

• Non-essential: Omega-9 (oleic acid)

• Monounsaturated: Omega-9 (olive oil)

• Polyunsaturated: Omega-3 (flaxseed, fish), Omega-6 (corn oil)

Trans Fats

• Production: Created by hydrogenation of unsaturated fats.

• Health effects: Increase LDL ("bad") cholesterol, decrease HDL ("good") cholesterol; raise risk of heart disease.

Other Lipids: Phospholipids and Cholesterol

• Phospholipids: Major component of cell membranes; emulsifiers in food.

• Cholesterol: Component of cell membranes, precursor for steroid hormones and vitamin D; found only in animal products.

Lipid Digestion

• Begins: In mouth (lingual lipase), continues in stomach (gastric lipase), mainly in small intestine (pancreatic lipase).

• Bile: Produced by liver, stored in gallbladder; emulsifies fats for digestion.

• Micelles: Small fat droplets formed by bile, aid in absorption.

Lipid Absorption

• Absorption: Fatty acids and monoglycerides absorbed into enterocytes (intestinal cells).

• Chylomicrons: Lipoproteins formed in enterocytes; transport dietary lipids via lymphatic system.

Lipid Transport

• Initial transport: Lymphatic system, then bloodstream.

• Chylomicrons: Deliver dietary triglycerides to tissues.

• Liver: Processes chylomicron remnants; produces VLDL (very low-density lipoprotein), LDL (low-density), HDL (high-density).

• VLDL: Transports endogenous triglycerides; becomes LDL after triglyceride removal.

• HDL: Removes cholesterol from tissues; protective against heart disease.

Cardiovascular Disease

• Heart attack: Blockage of coronary arteries.

• Stroke: Blockage or rupture of brain blood vessels.

• Peripheral Artery Disease: Narrowing of arteries in limbs.

• Risk factors: High LDL, low HDL, hypertension, smoking, diabetes, obesity.

Proteins

Functions of Proteins

• Structural support (muscle, skin, hair)

• Enzymes and hormones

• Immune function (antibodies)

• Transport (hemoglobin)

• Fluid and pH balance

Structure and Composition

• Proteins: Polymers of amino acids linked by peptide bonds.

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

• Distinguishing feature: Side chain (R group) gives each amino acid unique properties.

Protein Structure

• Primary: Sequence of amino acids.

• Secondary: Local folding (alpha-helix, beta-sheet).

• Tertiary: 3D shape of a single polypeptide.

• Quaternary: Multiple polypeptide chains.

• Denaturation: Loss of structure due to heat, pH, or chemicals; affects function.

Protein Digestion

• Begins: In stomach (pepsin, HCl denatures proteins).

• Continues: In small intestine (pancreatic proteases, brush border enzymes).

• Absorption: Amino acids absorbed in small intestine.

Protein Metabolism

• Excess amino acids: Deaminated; carbon skeleton used for energy or stored as fat.

• Protein turnover: Continuous breakdown and synthesis of proteins.

• Nitrogen balance: Balance between nitrogen intake and loss; positive in growth, negative in illness.

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

• Deamination: Removal of amino group for excretion.

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

• High-protein diets: May aid weight loss but can stress kidneys.

• Undernutrition: Marasmus (severe energy deficiency), Kwashiorkor (protein deficiency with adequate energy).

• Food protein disorders: Celiac disease (autoimmune reaction to gluten), non-celiac gluten sensitivity.

Enzymes in Digestion

Carbohydrate-Digesting Enzymes

• Salivary amylase (mouth)

• Pancreatic amylase (small intestine)

• Brush border enzymes: maltase, sucrase, lactase (small intestine)

Lipid-Digesting Enzymes

• Lingual lipase (mouth)

• Gastric lipase (stomach)

• Pancreatic lipase (small intestine)

Protein-Digesting Enzymes

• Pepsin (stomach)

• Trypsin, chymotrypsin, carboxypeptidase (pancreas, active in small intestine)

• Brush border peptidases (small intestine)

Brush Border Enzymes

• Located on microvilli of small intestine epithelial cells.

• Digest disaccharides and small peptides.

Vitamins and Minerals

Vitamins

• Description: Organic compounds required in small amounts for normal metabolism.

• Function: Coenzymes, antioxidants, hormone synthesis.

• Classification:

  • Water-soluble: B-complex, vitamin C

  • Fat-soluble: Vitamins A, D, E, K

Minerals

• Description: Inorganic elements essential for body functions.

• Function: Bone structure, fluid balance, nerve transmission.

• Classification:

  • Major minerals: Needed in larger amounts (e.g., calcium, potassium, sodium)

  • Trace minerals: Needed in small amounts (e.g., iron, zinc, iodine)

Free Radicals and Antioxidants

• Free radicals: Unstable molecules that can damage cells.

• Antioxidants: Compounds (e.g., vitamins C, E, selenium) that neutralize free radicals.

• Imbalance: Excess free radicals cause oxidative stress, linked to aging and chronic diseases.

Phytochemicals

• Definition: Non-nutrient compounds in plants with health benefits.

• Function: Antioxidant, anti-inflammatory, may reduce risk of chronic diseases.

Key Calculations and Concepts

• AMDR (Acceptable Macronutrient Distribution Ranges):

  • Carbohydrates: 45-65% of total calories

  • Fats: 20-35% of total calories

  • Proteins: 10-35% of total calories

• Protein requirement calculation:

  • For an adult: $\text{Protein (g)} = \text{Body weight (kg)} \times 0.8$

Sample Table: Comparison of Macronutrients

Macronutrient	Primary Function	Energy Yield (kcal/g)	AMDR (%)
Carbohydrates	Energy	4	45-65
Fats	Energy, cell structure	9	20-35
Proteins	Structure, enzymes	4	10-35

Chronic Diseases and Deficiency Disorders

• Excess macronutrients: Obesity, type 2 diabetes, cardiovascular disease.

• Deficiency diseases:

  • Protein: Marasmus, kwashiorkor

  • Vitamins: Scurvy (vitamin C), rickets (vitamin D), anemia (vitamin B12, iron)

  • Minerals: Osteoporosis (calcium), goiter (iodine)

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard academic knowledge in nutrition science.