2024 - Nutrients nutrient sensing system (1)

Learning Objectives

  • Understand the basic characteristics of major nutrients including their structures, functions, and significance.

  • Grasp the fate of carbohydrates, proteins, and lipids after ingestion.

  • Recognize biochemical and pathological consequences of disordered amino acid metabolism (e.g., Phenylketonuria) and carbohydrate absorption issues (e.g., Lactase deficiency).

  • Comprehend the body's mechanisms for sensing glucose and other nutrients, including the involvement of receptors like G-protein coupled receptors.

Introduction to Nutrition

  • Importance of macronutrients in human health.

  • Types of nutrients:

    • Carbohydrates

    • Fats

    • Proteins

    • Vitamins and Minerals

Roles of Nutrients in Humans

  • Energy: Primary source of fuel for biological processes.

  • Building Materials: Fundamental for growth and maintenance of body structures.

  • Regulatory Compounds: Involved in metabolic processes and signaling pathways.

Macronutrients Overview

  • Carbohydrates:

    • Simple Carbohydrates: Mono- and disaccharides.

    • Complex Carbohydrates: Polysaccharides such as starch and glycogen.

    • Dietary Fiber: Important for digestive health.

  • Fats:

    • Includes triacylglycerols, phospholipids, and cholesterol.

  • Proteins and Amino Acids:

    • Importance of nitrogen balance and protein quality.

Energy Calculation from Macronutrients

  • Energy Content:

    • Protein: 4 kcal/g

    • Fats: 9 kcal/g

    • Carbohydrates: 4 kcal/g

    • Alcohol: 7 kcal/g

Contribution of Macronutrients to Energy Expenditure

  • Energy for vital functions (cellular maintenance, metabolism, etc.).

  • Diet-induced thermogenesis (energy used for digestion and absorption).

  • Basal Metabolic Rate (BMR) for adults: Male: 1800 kcal, Female: 1300 kcal.

Dietary Carbohydrates

  • Types of Carbohydrates:

    • Monosaccharides: Simplest form (e.g., glucose, fructose).

    • Disaccharides: Consist of two monosaccharides (e.g., sucrose, lactose).

    • Polysaccharides: Long chains (e.g., starch, glycogen).

    • Fiber: Indigestible, beneficial for gut health.

Polysaccharides

  • Starch: Composed of amylose and amylopectin; used for energy storage.

  • Glycogen: Main carbohydrate reserve in the body, more branched than starch.

  • Cellulose: Forms plant cell walls; non-digestible fiber.

Dietary Fiber

  • Indigestible carbohydrates found only in plant foods.

  • Benefits include promoting satiety, detoxification, and reduced risks of several diseases (heart disease, diabetes).

  • Types: Soluble and insoluble fibers; important for digestive health.

High Fiber Foods

  • Examples include brown rice, beans, avocados, and raspberries.

  • Recommendations based on age and gender for daily fiber intake.

Fats

  • Types of Dietary Fats:

    • Triglycerides: Main energy source from dietary fats.

    • Phospholipids and Sterols: Structural components of cells.

  • Fatty Acids: Saturated, trans, monounsaturated, and polyunsaturated; variations impact cardiovascular health.

Essential Fatty Acids

  • Functions include membrane formation, brain development, and hormone production.

  • Symptoms of deficiency: Scaly dermatitis, hair loss, delayed healing.

Proteins

  • Composed of amino acid polymers (20 types).

  • Functions include structural roles, hormones, enzymes, and signaling.

Amino Acid Classification

  • Categories: Nonpolar, polar, acidic, basic, based on side chains.

  • Peptide bonds form between amino acids.

Phenylketonuria (PKU)

  • Genetic disorder affecting amino acid metabolism.

  • Requires dietary management to avoid phenylalanine and ensure adequate tyrosine intake.

Nutrient Digestion

  • Carbohydrate Digestion: Begins with salivary amylase, continues in the small intestine with pancreatic amylase; lactose intolerance due to lactase deficiency.

  • Lipid Digestion: Primarily occurs in the small intestine; involves bile salts and pancreatic lipase.

  • Protein Digestion: Enzymatic breakdown in the stomach and small intestine.

Nutrient Sensing Mechanisms

  • Taste receptors in the mouth and gut sense the presence of various nutrients and affect appetite regulation.

  • Importance of hormone responses related to nutrient intake (e.g., ghrelin and insulin).

Conclusion

  • The importance of a balanced diet comprising carbohydrates, fats, and proteins for overall health and nutrient sensing mechanisms.