Essential Nutrients: Macronutrients and Micronutrients

Overview

• Nutrients are substances in food that promote normal growth, repair, and maintenance in the body.
• The body efficiently breaks down and absorbs nutrients.
• There are 40 essential nutrients the body cannot produce quickly enough, requiring dietary intake.
• Calories are the units measuring energy stored in food's chemical bonds.

6 Essential Nutrients

• The six essential nutrients are water, carbohydrates, lipids/fats, proteins, vitamins, and minerals.
• Nutrients are split into macronutrients and micronutrients.
• Macronutrients are carbohydrates, lipids/fats, and proteins.
• Micronutrients are vitamins and minerals.

Carbohydrates

• Dietary sources of carbohydrates include plants, simple sugars in fruits, and starches in grains and vegetables.
• Lactose in milk is also a dietary source of carbohydrates.
• Glucose from carbohydrates fuels body cells with ATP.
• ATP is unstable which necessitates glucose or glycogen for storage.
• 45-65% of total caloric intake should be from from carbohydrates.

Lipids/Fats

• Dietary sources include meat, dairy, some plants (avocados/coconuts), and oils.
• Omega 6 and 3 fatty acids cannot be synthesized by the body, and must be consumed.
• Fats are used for protective cushioning, insulation, energy storage, phospholipids in cell membranes, etc.
• 20-30% of total caloric intake should be from fats, with saturated fats being 10% or less.

Proteins

• Dietary sources include eggs, milk, fish, meat, beans, and nuts.
• Nine of the 20 essential amino acids cannot be synthesized so they must be consumed.
• Proteins are essential for structural uses like connective tissues and muscles.
• Functional uses of proteins include enzymes, hormones, and transport.
• Protein dietary requirements depend on age/size/metabolic rate, needing 0.8 g of protein per kg of body weight in general.

Vitamins

• Vitamins are organic compounds that help the body to use nutrients.
• Most vitamins function as coenzymes acting alongside enzymes.
• For example, Vitamin B acts as a coenzyme in the oxidation of glucose for energy.
• Vitamins can be water-soluble or fat-soluble.
• Water-soluble vitamins (B-complex and C) are absorbed with water in the GI tract.
• Water-soluble vitamins are not stored in the body; they get excreted if not taken into a cell within an hour,
• Fat-soluble vitamins (A, D, E, and K) are absorbed with other lipids in the small intestine.
• The body can store fat-soluble vitamins.

Minerals

• Minerals are inorganic chemical compounds, or salts, found in nature.
• They don't provide fuel, but make body structures stronger and bind to organic compounds or get ionized in body fluids.
• Iron (Fe) is a key component of hemoglobin.
• Sodium (Na) and Chlorine (Cl) ions are key electrolytes in blood.
• Calcium (Ca), phosphorus (P), sulfur (S), potassium (K), chlorine (Cl), sodium (Na), and magnesium (Mg) should be consumed at least 200 mg each day; all other minerals are needed only in trace amounts.

Metabolism

• Metabolism includes all biochemical reactions in the body.
• Anabolic reactions link simple molecules to make complex ones, requiring an overall consumption of energy.
• Catabolic reactions break down complex molecules into smaller ones, producing an overall release of energy.
• Digestion is a catabolic reaction using enzymes in the alimentary canal (mainly the small intestine).
• Energy output results in heat loss to maintain homeostatic body temperature, mainly regulated by the hypothalamus.

Stages of Metabolism

• There are 3 stages of processing food for energy.
• Digestion and absorption occurs in the GI tract, before nutrients are transported by the blood.
• Nutrients can be built into other macromolecules (anabolic reaction)
• Nutrients can be processed for energy (catabolic reaction) through glycolysis
• Glycolysis occurs in the cytoplasm of cells.
• Citric Acid Cycle and ETC (oxidative phosphorylation) occurs in the mitochondria.

Nutritional States

• There are two nutritional states: absorptive and postabsorptive.

Absorptive State

• The absorptive state, or "fed state", lasts about 4 hours after eating.
• Nutrients move from the GI tract into the blood.
• Anabolism storing nutrients exceeds catabolism.
• Glucose is the major energy fuel.
• Any excess glucose is converted to and stored as fat or glycogen.
• Insulin controls/directs the absorptive state.

Postabsorptive State

• The postabsorptive state is the fasting state when the GI tract is empty.
• Catabolism exceeds anabolism, stopping the synthesis of fats, glycogen, and proteins for the body’s needs.
• Major energy fuel during the postabsorptive state is body reserves so glucose is available for the brain.
• Glucose comes from breaking down glycogen in the liver, breaking down glycogen in skeletal muscles, converting glycerol from adipose tissues in the liver, and, as a last resort, breaking down proteins from tissues.
• Glucagon and the sympathetic nervous system controls/directs the postabsorptive state.

Liver

• The liver processes most nutrients and regulates plasma cholesterol levels.
• Cholesterol, a steroid made by the liver, is in many body tissues and is a major component of the plasma membrane.
• Cholesterol is the structural basis for bile salts, steroid hormones, and vitamin D.
• The liver makes lipoproteins for transporting lipids (like cholesterol) in the blood.
• Lipoproteins regulate entry/exit from specific target cells in the liver.