Anabolism and Catabolism

• Nutrition is the study of how living organisms obtain and utilize nutrients needed for growth and to sustain life.
• Nutrients consist of most bimolecules, vitamins, and minerals.
• Nutrients are required for the synthesis of new molecules, energy production, for maintenance, growth, and repair.
• Nutrients obtained through food, e.g. water.
• Nutrient levels are regulated during and following meals

Anabolism

• The synthesis of complex molecules in living organisms from simpler ones; constructive metabolism.
• Requires energy

Catabolism

• The breakdown of complex molecules in living organisms to form simpler ones; destructive metabolism.
• Releases energy

Macronutrients vs. Micronutrients

• Macronutrients are nutrients required in large amounts whereas micronutrients are nutrients needed in small amounts
• Examples of macronutrients: protein, fat, fiber, water, and carbohydrate.
• Rich in macronutrients: cereals, legumes, meat, fish, yams, potatoes, nuts, and oil seeds
• Examples of micronutrients: phytochemicals and antioxidants, vitamins, and certain minerals
• Rich in micronutrients: vegetables, fruits, eggs, green leafy vegetables, and fermented foods.
• While macronutrients contribute to bulk energy needed for the metabolic system, micronutrients help various body functions, growth, and disease prevention

Carbohydrates

• Structurally classified as monosaccharides (e.g., glucose, fructose, galactose), disaccharides (e.g., sucrose, lactose, maltose) or polysaccharides (e.g., starches and fibers)
• In terms of dietary sources, carbohydrates are classified as sugars (monosaccharides, disaccharides, dextrose, brown sugar, honey, molasses), starch (e.g., tubers, grains, beans), and fiber, consisting of fibrous molecules from plants and animals, unabsorbed by the GI.

Lipids

• These include triglycerides, sterols (cholesterol), phospholipids, and eicosanoids
• Triglycerides composed of glycerol and are divided into saturated, unsaturated, or polyunsaturated.
• Sterols required as component of plasma membrane as well as a precursor hormone for steroid hormones, bile salts, vitamin D
• Sterols comes from diet or metabolic pathway in liver
• Phospholipids make up the cell membrane and have hydrophilic head and hydrophobic tails x2
• Eicosanoids are signaling molecules like Prostaglandins, Leukotrienes, and Thromboxanes

Saturated fatty acids

• Sources are solid at room temperature
• Dietary sources: fat in meat, milk, cheese, coconut oil, palm oil

Unsaturated fatty acids

• Sources are liquid at room temperature
• Dietary sources: nuts, certain oils—canola oil, olive oil, sunflower

Polyunsaturated fatty acids

• Contain two or more double bonds, that are liquid at room temperature
• Dietary sources are certain oils—soybean oil, corn oil, and safflower oil

Proteins

• They are the most structurally and functionally diverse molecules
• Needed in adequate quantities to replace worn out protein structures.
• Nine amino acids are essential, while the body can synthesize 11.
• These amino acids are used to synthesize new proteins in the body

Complete proteins

• Contain all essential amino acids
• Animal proteins

Incomplete proteins

• Do not contain all essential amino acids
• Plant proteins
• Essential amino acids can be provided by combining dishes containing plant protein.

Vegetarian

• Consumption of meat, poultry, and fish is avoided
• Lacto-ovo vegetarians do not eat animal flesh, but consume milk, eggs, and cheese
• Vegans do not eat any animal products, and must get essential amino acids through complementary protein sources, and not necessarily at the same meal, but regularly.

Vitamins

• They are organic molecules required for normal metabolism, present in small quantities in food and drink.
• Do not provide any energy (calories), but play roles in metabolic processes.
• Vitamins are categorized as water-soluble (vitamin B complex and vitamin C) or fat-soluble
• Essential and non-essential are also a categorization method
• Sourced from meat, eggs, beans, legumes, fruit, vegetables, and fish
• Water-soluble vitamins (B-complex and vitamin C) readily absorbed in bloodstream via digestive tract, and excess is secreted.
• Fat-soluble vitamins (A, D, E & K) absorbed with lipid micelles, and excess stored in fat cells

Functions of fat-soluble vitamins

• Vitamin A: pre-curser for the formation of the visual pigment retinal
• Vitamin E: helps stabilize and prevent damage to cell membranes
• Vitamin K: required for the synthesis of specific blood-clotting proteins
• Vitamin D: Increases calcium absorption from the GI tract.

Minerals

• All minerals are essential and must be obtained in the diet
• Iron present in hemoglobin within erythrocytes, where it binds oxygen; also present in the mitochondria as part of the electron transport system, to bind electrons
• Calcium required to form and maintain the skeleton, muscle contraction, and exocytosis of neurotransmitters; also plays an important role in blood clotting
• Sodium and Potassium function is to maintain a resting membrane potential in excitable cells and are also needed to propagate an action potential
• Iodine is required to produce thyroid hormone
• Zinc plays an important role in protein synthesis and wound healing

Absorptive State

• Time spent eating, digesting, and absorbing nutrients
• Lasts four hours after a meal
• Concentrations of glucose, triglycerides, and amino acids increase as absorbed from intestines

Insulin

• Major regulatory hormone released during absorptive state in the pancreas
• Released in response to increased blood glucose levels, which stimulates liver and muscle cells
• Enhances uptake of triglycerides from blood, stimulates lipogenesis, and stimulates most cells to increase amino acid uptake
• Forms glycogen from glucose and inhibits lipolysis, causing accelerated protein synthesis from the GI tract.

Postabsorptive State

• The time between meals
• Body relying on stores of nutrients and works to maintain homeostatic levels of nutrients via glucagon
• Major regulatory hormone during postabsorptive state
• Released in response to decreasing blood glucose levels
• It stimulates liver to increase breakdown of glycogen to glucose, Gluconeogenesis is stimulated from noncarbohydrate sources, and breakdown of triglycerides from adipose tissue
• Postabsorptive State has no effect on amino acids or proteins in cells

Liver and Cholesterol Synthesis

• Process achieved via hepatocytes, with fatty acids transported in blood, with Cholesterol produced at a basal level, and varies among individuals
• Cholesterol synthesis decreased with higher cholesterol intake, and vice versa

Forms of Cholesterol Release

• Released into blood in very-low-density lipoproteins
• Synthesized into bile salts (90% these reabsorbed moving through ileum versus 10% lost in feces, bile bound to fiber)

Lipoproteins

• Lipids with protein to facilitate transport, formed in liver, and classified by relative density
• Very-low-density lipoproteins (VLDL) have the most lipid
• Low-density lipoproteins (LDL) have less lipid
• High-density lipoproteins (HDL) have the least amount of lipid

Transport from Liver (VLDLs and LDLs)

• VLDLs have types of lipids with protein, assembled in the liver, and released into blood.
• VLDLs circulate in blood and release triglycerides to peripheral tissues, primarily adipose tissue
• LDLs contain high amounts of cholesterol, deliver cholesterol to cells, and bind to LDL receptors in the plasma membrane of cell (engulfed by endocytosis)
• The cholesterol is subsequently incorporated into plasma membrane and used by certain tissues to produce steroid hormones

Transport from Peripheral Tissues to the Liver

• It involves HDLs with proteins sent into blood without any lipids
• It circulates through blood and fill with lipids from peripheral tissue.
• Like LDLs, HDLs make cholesterol available to steroid-producing tissue.
• Unlike LDLs, HDLs are not engulfed, and lipids are transported via HDLs to liver.
• Excess cholesterol is converted into bile salts within the liver

Liver functions

• Carbohydrate metabolism involving gluconeogenesis, glycogen formation and breakdown, fructose and galactose converted to glucose
• Protein metabolism: Amino acids used to make proteins, urea elimination, and the conversion of amino acids
• Lipid metabolism involving formation and breakdown of triglycerides, cholesterol Synthesis, ketone bodies formation
• Transport of lipids via VLDL, LDL, and HDL
• Other factors include storage and drug detoxification

Clinical blood cholesterol levels

• Risk factors for cardiovascular disease: High levels of LDLs or total cholesterol, and low blood levels of HDLs
• LDLs are referred to as "bad" cholesterol because excess cholesterol deposits on inner arterial walls
• HDLs are referred to as ""good” cholesterol” and it transports lipid from arterial wall to liver

ATP cellular respiration

• Glycolysis: Anaerobic metabolic pathway in the cytoplasm to oxidize glucose to 2 pyruvate molecules, forming 2 ATP and 2 NADH from NAD+
• Pyruvate turns to lactate if oxygen is scarce
• Intermediate stage: Pyruvate is converted to Acetyl CoA, CO2 formed and NADH
• Acetyl CoA forms citric acid and then CO2, ATP, FADH2, and NADH are created in cycle
• Electron transport: Transfer of hydrogen and electron from NADH and FADH2, where Oxidative phosphorylation produces ATP

Lipid and protein metabolism alternate sources of ATP

• Protein-derived ATP via amino acid-derived ATP (removal of amine group via deamination in liver hepatocytes
• Amine group converts to urea for kidney removal
• Remainder of proteins then enters a metabolic pathway dependant on specific amino acid, which can then lead to glycolysis, intermediate stage, or citric acid cycle

Sources of ATP from triglyceride digestion

• Produces glycerol and fatty acids where glycerol can be converted to glucose for ATP production in cell metabolism
• Fatty acids can be oxidized and enter Krebs cycle to produce ATP

Nutrient interconversion

• Changing of one nutrient biomolecule into another
• Due to biochemical pathways associated with cellular respiration
• Example, glucose broken down to acetyl CoA, which then synthesized into triglycerides and stored instead of entering citric acid cycle
• Additionally, example where a low-carbohydrate diet of protein and fat can lead to a reversal of biochemical pathways of cellular respiration, converted to glucose.