Chapter 18

Chapter 18: Nutrition and Metabolism

18.1 Overview of Nutrition and Metabolism

  • Nutrition: Study of nutrients and how the body uses them.

  • Nutrients: Chemicals from the environment needed for survival; provide energy and building blocks for molecules.

    • Macronutrients: Required in large quantities (carbohydrates, lipids, proteins); provide energy.

    • Micronutrients: Required in smaller amounts (vitamins, minerals); help extract energy from macronutrients.

  • Essential Nutrients: Nutrients that cannot be synthesized by the body or cannot be produced in sufficient quantity; must be obtained from the diet.

  • Calories: Units of heat used to express the amount of energy in foods.

18.2 Carbohydrates

  • Carbohydrates: Organic compounds (sugars, starches) used for energy.

    • Sources:

      • Polysaccharides: Complex carbohydrates like starch and glycogen.

      • Disaccharides: Include milk sugar, cane sugar, beet sugar.

      • Monosaccharides: Simple sugars from honey and fruits. GLUCOSE

  • Digestion: Breaks down complex carbohydrates into monosaccharides for absorption.

  • Cellulose: Complex carbohydrate providing fiber, not digestible by humans.

Carbohydrate Use

  • Different monosaccharides absorbed: fructose, galactose, glucose.

  • Glucose is the primary energy source; other monosaccharides convert to glucose.

  • Glycolysis: Breakdown of glucose into CO2, H2O, and energy.

  • Glycogenesis: Conversion of excess glucose to glycogen for storage in liver/muscle cells.

  • Glycogenolysis: Breakdown of glycogen back into glucose when energy is needed.

  • Lipogenesis: Conversion of excess glucose to fats for storage.

  • Gluconeogenesis: Conversion of noncarbohydrates (amino acids, glycerol) into glucose when needed.

18.3 Lipids

  • Lipids: Organic compounds including fats, oils, phospholipids, and cholesterol.

    • Provide energy and structural components (e.g., cell membranes).

    • Triglycerides: Composed of glycerol and three fatty acids; main dietary lipid.

Lipid Sources

  • Saturated Fats: Found in animal products and certain plant oils; linked to cardiovascular disease.

  • Unsaturated Fats: Found in seeds, nuts, and plant oils; healthier fats.

  • Cholesterol: Present in animal products; absent in plant-based foods.

Lipid Use

  • Function mainly to supply energy; higher energy content per gram compared to carbohydrates and proteins.

  • Triglycerides broken down into glycerol and fatty acids for energy release.

  • Lipids make the most calories.

  • Essential Fatty Acids: Must be obtained from diet; liver cannot synthesize them.

  • Lipoproteins formed by combining lipids with proteins, aiding in lipid transport.

  • VLDLs (very low density lipoproteins): high triglyceride content

  • LDLs (low density lipoproteins): high cholesterol content

  • HDLs (high density lipoproteins): high protein content

18.4 Proteins

  • Proteins: Chains of amino acids with various functions (structural, enzymatic, hormonal, etc.).

    • Provide energy after being broken down into amino acids.

    • CHON - nitrogen think urea, waste, which is produced during the breakdown of proteins and excreted by the kidneys.

  • Deamination: Removal of amino groups from amino acids to form urea.

  • Excess amino acids can be converted into glucose or fat.

Nitrogen Balance

Negative nitrogen balance: develops from starvation (excretion exceeds intake)

Positive nitrogen balance: develops in growing children, pregnant woman, athletes (protein being built into new tissue exceeds energy usage and excretion)

Protein Sources

  • High-Quality Proteins: Complete proteins provide all essential amino acids; found in animal products.

  • Low-Quality Proteins: Incomplete proteins are low in essential amino acids; found in plant sources.

  • Combining different plant proteins can create a complete amino acid profile.

  • Energy Balance: When calorie intake equals expenditure, body weight remains stable.

    • Positive Energy Balance: Excess caloric intake leading to weight gain.

    • Negative Energy Balance: Caloric expenditure exceeding intake, causing weight loss.

18.6 Appetite Control

  • Appetite: Drive to seek food controlled by the hypothalamus and influenced by hormones (insulin, leptin, neuropeptide Y, ghrelin).

    • Insulin: Promotes fat storage and suppresses appetite post-meal. (from pancreas)

    • Leptin: Secreted by adipose tissues; inhibits appetite. (from adipocytes)

    • Ghrelin: Secreted by the stomach; stimulates appetite. (from stomach)

    • Neuropeptide Y: Responds to the hormone Ghrelin and stimulates appetite, as well. (from hypothalamus)

18.7 Vitamins

  • Vitamins: Organic compounds necessary in small amounts for metabolic processes.

    • Fat-Soluble Vitamins: A, D, E, and K.

    • Water-Soluble Vitamins: B (bones, blood) complex and vitamin C (collagen).

Fat-Soluble Vitamins

  • Stored in bodily tissues; excessive intake leads to toxicity.

Water-Soluble Vitamins

  • Require careful intake to avoid deficiencies; cooking may destroy some.

18.8 Minerals

  • Minerals: Inorganic elements necessary for various metabolic processes, primarily obtained from plants and animal products.

    • Major Minerals: Include calcium, phosphorus, potassium, etc.

    • Trace Elements: Include iron - hemoglobin, zinc, copper, etc.