Macronutrients in Nutrition

Macronutrients

• Carbohydrates:
  • Provide energy for the body (4 kcal/g)
  • Classified into simple (sugars) and complex (polysaccharides) forms
  • Important sources: grains, fruits, vegetables, and dairy products
• Proteins:
  • Build and repair tissues (4 kcal/g)
  • Composed of amino acids (20 standard amino acids)
  • Essential amino acids (9) cannot be synthesized by the body and must be obtained through diet
  • Important sources: meat, fish, eggs, dairy products, and legumes
• Fats:
  • Provide energy and absorb fat-soluble vitamins (9 kcal/g)
  • Classified into saturated and unsaturated forms
  • Important sources: oils, fatty fish, nuts, and seeds

Micronutrients

• Vitamins:
  • Fat-soluble: A, D, E, and K
  • Water-soluble: B vitamins (8) and C
  • Function as coenzymes, antioxidants, and hormone regulators
• Minerals:
  • Macro-minerals: calcium, phosphorus, magnesium, potassium, sodium, and chloride
  • Micro-minerals (trace elements): iron, zinc, iodine, selenium, copper, and others
  • Involved in enzyme functions, nerve transmission, and bone health

Metabolic Pathways

• Glycolysis: breakdown of glucose to pyruvate (anaerobic)
• Citric Acid Cycle (Krebs Cycle): breakdown of acetyl-CoA to ATP, NADH, and FADH2 (aerobic)
• Fatty Acid Oxidation: breakdown of fatty acids to acetyl-CoA
• Protein Synthesis: assembly of amino acids into proteins

Hormone Regulation

• Insulin: regulates glucose uptake and storage
• Glucagon: regulates glucose release from storage
• Thyroid Hormones: regulate metabolic rate
• Adrenaline (Epinephrine): regulates energy metabolism and response to stress

Nutrient Interactions and Deficiencies

• Synergistic effects: nutrients work together to produce a greater effect
• Antagonistic effects: nutrients counteract each other's effects
• Deficiencies: can lead to various diseases and disorders, such as scurvy (vitamin C), rickets (vitamin D), and anemia (iron)

Macronutrients

• Carbohydrates provide energy for the body, with 4 kcal of energy per gram.
• They are classified into simple (sugars) and complex (polysaccharides) forms.
• Important sources of carbohydrates include grains, fruits, vegetables, and dairy products.
• Proteins build and repair tissues, with 4 kcal of energy per gram.
• They are composed of amino acids, with 20 standard amino acids and 9 essential amino acids that cannot be synthesized by the body.
• Important sources of proteins include meat, fish, eggs, dairy products, and legumes.
• Fats provide energy and absorb fat-soluble vitamins, with 9 kcal of energy per gram.
• They are classified into saturated and unsaturated forms.
• Important sources of fats include oils, fatty fish, nuts, and seeds.

Micronutrients

• Vitamins are classified into fat-soluble (A, D, E, and K) and water-soluble (B vitamins and C).
• They function as coenzymes, antioxidants, and hormone regulators.
• Minerals are classified into macro-minerals (calcium, phosphorus, magnesium, potassium, sodium, and chloride) and micro-minerals (trace elements).
• Minerals are involved in enzyme functions, nerve transmission, and bone health.

Metabolic Pathways

• Glycolysis is the breakdown of glucose to pyruvate, an anaerobic process.
• The citric acid cycle (Krebs cycle) is the breakdown of acetyl-CoA to ATP, NADH, and FADH2, an aerobic process.
• Fatty acid oxidation is the breakdown of fatty acids to acetyl-CoA.
• Protein synthesis is the assembly of amino acids into proteins.

Hormone Regulation

• Insulin regulates glucose uptake and storage.
• Glucagon regulates glucose release from storage.
• Thyroid hormones regulate metabolic rate.
• Adrenaline (epinephrine) regulates energy metabolism and response to stress.

Nutrient Interactions and Deficiencies

• Synergistic effects occur when nutrients work together to produce a greater effect.
• Antagonistic effects occur when nutrients counteract each other's effects.
• Deficiencies in nutrients can lead to various diseases and disorders, such as scurvy (vitamin C deficiency), rickets (vitamin D deficiency), and anemia (iron deficiency).

Glycemic Control

Definition

• Glycemic control is the regulation of blood sugar levels to maintain a stable and healthy range.

Importance

• Optimal blood sugar levels prevent and manage diseases like diabetes, cardiovascular disease, and obesity.
• Glycemic control is essential for energy homeostasis, cognitive function, and overall health.

Mechanisms of Glycemic Control

• Glucagon stimulates glycogenolysis and gluconeogenesis to increase blood glucose levels.
• Insulin promotes glucose uptake in cells, inhibits glycogenolysis and gluconeogenesis, and stimulates glycogen synthesis.
• Cortisol, growth hormone, and thyroid hormone are counter-regulatory hormones that increase blood glucose levels.
• The sympathetic nervous system stimulates glycogenolysis and gluconeogenesis.
• The parasympathetic nervous system promotes insulin secretion and glucose uptake.

Factors Affecting Glycemic Control

• Consuming high-carbohydrate, high-fiber, or low-glycemic index foods regulates blood sugar levels.
• Regular physical activity improves insulin sensitivity and glucose uptake.
• Chronic stress leads to insulin resistance and impaired glycemic control.
• Adequate sleep is essential for maintaining optimal glycemic control.
• Genetic predisposition affects an individual's ability to regulate blood sugar levels.

Clinical Implications

• Diabetes is a disease characterized by impaired glycemic control, leading to hyperglycemia and associated complications.
• Hypoglycemia is a condition characterized by low blood sugar levels, often resulting from excessive insulin secretion or insulin sensitivity.
• Metabolic Syndrome is a cluster of conditions, including insulin resistance, glucose intolerance, and cardiovascular disease risk factors.

Carbohydrate Metabolism

• Starch is a complex carbohydrate composed of amylose and amylopectin
• Salivary amylase breaks down starch into maltose and dextrins in the mouth
• Pancreatic amylase further breaks down maltose and dextrins into maltose in the small intestine
• Maltase converts maltose into glucose, which is then absorbed into the bloodstream

Dietary Fiber

• Dietary fiber is a type of carbohydrate that is not digestible by human enzymes
• Fiber is classified into soluble (e.g. pectin, gum) and insoluble (e.g. cellulose, hemicellulose) types
• Gut microbiota ferments fiber in the large intestine, producing short-chain fatty acids (SCFAs)
• SCFAs can be used as energy by the host or excreted in the feces

Glucose Transport and Uptake

• Glucose is transported across the cell membrane through facilitated diffusion
• GLUT proteins (e.g. GLUT2, GLUT4) are specific transporters for glucose
• Sodium-glucose cotransport uses the energy from sodium gradients to transport glucose
• Insulin stimulates the translocation of GLUT4 to the cell surface, increasing glucose uptake in muscle and adipose tissue

Glycogen Metabolism

• Glycogen is a complex carbohydrate stored in the liver and muscle
• Glycogen synthase adds glucose molecules to the growing glycogen chain during synthesis
• Insulin stimulates glycogen synthesis, while glucagon inhibits it
• ATP and glucose-6-phosphate are allosteric activators of glycogen synthase

Glycolysis

• Glycolysis is the first step in cellular glucose metabolism, converting glucose into pyruvate
• Glycolysis generates ATP and NADH through 10 enzyme-catalyzed reactions
• Key regulatory steps in glycolysis include:
  • Hexokinase phosphorylating glucose, trapping it in the cell
  • Phosphofructokinase 1 committing glucose to glycolysis
  • Pyruvate kinase regulating the final step of glycolysis, influenced by ATP and fructose-2,6-bisphosphate