Nutrition and Metabolism

Nutrition and Metabolism

Nutrition

• Process of obtaining/providing nutrients for health and growth.

• Nutrition significantly influences body weight.

• Most nutrients provide calories:

  • Caloric intake should match expenditure to maintain stable body weight.

  • Excess caloric intake without matched expenditure leads to weight gain.

• Body weight is affected by genetics, lifestyle, and microbiome.

Appetite

• Definition: Desire to eat.

• Regulation of Appetite:

  • Short-term hormones trigger hunger and satiety:

    • Ghrelin: Produced by parietal cells of the stomach, stimulates hunger.

    • Peptide YY: Secreted by enteroendocrine cells in the ileum and colon, inhibits hunger.

    • CCK (Cholecystokinin): Released from enteroendocrine cells in the duodenum and ileum, suppresses appetite.

    • Amylin: Released by beta cells of the pancreas, complements satiety signals.

  • Long-term hormones regulate appetite by modulating energy balance.

Long-term Appetite Regulation Hormones

• Leptin:

  • Released by adipocytes, signals fullness.

  • Levels proportional to fat content in the body.

  • Stimulates epinephrine release, promoting fat breakdown.

  • High levels can lead to unresponsive receptors, causing hyperphagia and obesity.

• Insulin:

  • Secreted by beta cells of the pancreas.

  • Promotes glucose utilization, glycogenesis, and lipogenesis in cells.

Brain Centers Regulating Eating

• Hypothalamus: Contains arcuate nucleus crucial for appetite regulation.

  • Neuropeptide Y: Appetite stimulant, blocked by insulin, Peptide YY, and leptin.

  • Melanocortin: Appetite suppressant, stimulated by leptin.

• Appetite control is complex and involves numerous factors.

Calorie Definition

• Definition: A calorie is the amount of heat needed to increase 1 gram of water by 1 degree centigrade.

• 1 Calorie (C) = 1000 Kilocalories (Kcal).

• Food labels typically display calories in kilocalories.

Caloric Content Per Gram of Nutrients

• Carbohydrates: 4 calories

• Proteins: 4 calories

• Fats: 9 calories

• Alcohol: 7 calories (considered "empty calories")

Nutrients

• Nutrients are categorized into two groups:

  • Macronutrients (needed in large amounts):

    • Carbohydrates

    • Proteins

    • Lipids (fats)

    • Water

  • Micronutrients (needed in small amounts):

    • Vitamins (organic):

      • Water-soluble (B vitamins, Vitamin C)

      • Fat-soluble (Vitamins A, D, E, K)

    • Minerals (inorganic): from earth's crust.

Vitamins Requirements for Adults (Selected)

• B-complex vitamins:

  • B1 (Thiamine): Meat, nuts, whole grains (1.1-1.2 mg) - Deficiency: Beriberi

  • B2 (Riboflavin): Meat, greens (1.1-1.3 mg) - Deficiency: Ariboflavinosis

  • B3 (Niacin): Meat, liver (14-16 mg) - Deficiency: Pellagra

  • B12 (Cyanocobalamin): Dairy, meat (2.4 mg) - Deficiency: Pernicious anemia

• Fat-Soluble Vitamins:

  • Vitamin A: (700-900 mg) - Deficiency: Night blindness

  • Vitamin D: (15 mg) - Deficiency: Rickets

Minerals Requirements for Adults (Selected)

• Major Minerals:

  • Calcium: Green vegetables, dairy (1000-1300 mg) - Deficiency: Osteoporosis

  • Potassium: Meat, fruits (4700 mg) - Deficiency: Muscle weakness

• Trace Minerals:

  • Iron: Red meat, dark leafy greens (8-18 mg) - Deficiency: Anemia

  • Zinc: Meat, seeds (8-11 mg) - Deficiency: Immune dysfunction

Essential vs Non-Essential Nutrients

• Essential Nutrients: Must be obtained from the diet.

  • Essential Fatty Acids: Linoleic and linolenic acids (omega 3 and omega 6).

  • Essential Amino Acids: 10 of 20 amino acids; complete proteins (animal sources) vs incomplete proteins (plant sources).

• Non-Essential Nutrients: Produced by the body from essential nutrients.

Carbohydrates

• Primary source of fuel for the body.

• Excess carbohydrates are converted into fat.

• Types of Carbohydrates:

  • Monosaccharides: Glucose, fructose, galactose.

  • Polysaccharides: Glycogen (storage form) and cellulose (fiber).

Lipids

• Function: Energy storage (triglycerides).

• Structure: Phospholipids, cholesterol required for fat-soluble vitamin absorption.

• Cholesterol is vital for plasma membranes, steroid hormones, bile salts, and Vitamin D synthesis.

• Hydrophobic nature: Needs transport molecules (lipoproteins).

Lipoproteins

• Types of Lipoproteins:

  • Chylomicrons: From intestines.

  • VLDL: From liver.

  • LDL: Derived from VLDL (bad cholesterol).

  • HDL: Initiates from the liver (good cholesterol).

Lipid Profiles

• Desirable Cholesterol Level: < 200 mg %.

• LDL: Negative health implications (bad cholesterol).

• HDL: Protective effects (good cholesterol).

Proteins

• Vital for numerous functions in the body.

• Differentiation between complete proteins (contain all essential amino acids) and incomplete proteins.

• Nitrogen Balance:

  • Positive Balance: More nitrogen intake than excretion, typical in growth phases, pregnancy.

  • Negative Balance: Indicator of muscle wasting.

Oxidation of Organic Molecules

• Oxidation process involves the removal of electrons and hydrogens from nutrients.

• Released electrons and hydrogens serve as energy for the body.

• Coenzymes: Function as electron shuttles during metabolic processes, derived mainly from B vitamins.

  • Important coenzymes include NAD and FAD.

Carbohydrate Metabolism

• In GI tract, carbohydrates are absorbed as glucose, fructose, and galactose.

• Pathways to Metabolize Glucose:

  • Glycolysis: Occurs in cytosol of all cells.

  • Anaerobic Fermentation: Occurs in the cytosol, produces lactic acid.

  • Aerobic Cellular Respiration: Requires oxygen, occurs in mitochondria.

Glycolysis

• Total of 10 reactions resulting in:

  • 2 Pyruvic acids (pyruvate)

  • Net gain of 2 ATPs

  • 2 NADH + H+

• Occurs in all body cells.

• Fate of Pyruvate:

  • Low oxygen: converts to lactic acid.

  • High oxygen: enters the Krebs cycle as AcetylCoA.

Krebs Cycle and Intermediate Steps

• Occurs in mitochondrial matrix.

• Pyruvic acid converts to AcetylCoA, producing 1 CO2 and 1 NADH.

• AcetylCoA oxidation generates:

  • 1 ATP

  • 2 CO2

  • 3 NADH + H+

  • 1 FADH2.

Cellular Respiration Overview

• Stages: Glycolysis ➔ Intermediate stage ➔ Citric Acid Cycle ➔ Electron Transport System.

Electron Transport Chain (ETC)

• Comprises enzyme complexes that move electrons and pump protons across membranes.

• The last electron acceptor is oxygen (O2).

• Chemiosmosis occurs as H+ ions flow back into the matrix through ATP synthase, producing ATP.

Other Carbohydrate Pathways

• Glycogenesis: Formation of glycogen when blood glucose is low; triggered by insulin.

• Glycogenolysis: Breakdown of glycogen for glucose; liver provides free glucose; triggered by glucagon and epinephrine.

• Gluconeogenesis: Synthesis of glucose from non-carbohydrate sources (e.g., glycerol, amino acids); occurs in liver and kidney; triggered by glucagon, cortisol.

Lipid Metabolism

• Main Pathways:

  • Lipogenesis: Formation of triglycerides from amino acids/glucose, triggered by insulin.

  • Lipolysis: Breakdown of triglycerides into glycerol and fatty acids, initiated by low insulin, epinephrine.

  • Beta-Oxidation: Fatty acids convert to AcetylCoA.

  • Ketogenesis: Formation of ketone bodies when insulin levels are low.

Protein Metabolism

• Proteins must be broken down for amino acid recycling.

• Deamination of amino acids in the liver removes amine groups; resulting ammonia is converted to urea for excretion.

• Cortisol may trigger protein breakdown under stress or illness.

Metabolic States

• Two primary metabolic states:

  • Absorptive State: Post-meal phase, lasts about 3 hours, an anabolic state dominated by insulin.

  • Post-absorptive State: Fasting period until next meal, focuses on maintaining blood glucose, involves glucagon, cortisol, and epinephrine.

Liver and Cholesterol Regulation

• The liver synthesizes the majority of cholesterol.

• Synthesis uses acetyl CoA with the action of HMG CoA reductase (target for statin medications).

• Bile salts formed from cholesterol aid fat digestion and absorption in the intestines.

Metabolic Rate

• Measurement of energy use at any given time, varies based on several factors.

• Basal Metabolic Rate (BMR): Energy used to maintain essential body functions at rest, influenced by age, sex, and muscle mass.

• Males typically have higher BMR than females, and BMR decreases with age.