Human Nutrition Vocabulary

Flashcards covering the key vocabulary and definitions from the Human Nutrition lecture notes. Topics include lipids, fatty acids, cholesterol, digestion, lipoproteins, and protein metabolism.

Fiber Daily Recommendation for Adults

Generic recommendation of 25g to 40g daily.

Sources of Fiber

Whole-grain products, vegetables, fruits, and legumes.

Main Types of Lipids

Fatty acids, TG (triglycerides), phospholipids, and sterols.

Functions of Lipids

Energy production and storage, insulation and padding, cell signaling, structural support, inflammatory responses, hormonal production.

Lipid Solubility

Generally insoluble in H2O, requiring specific processes for digestion, absorbance, and transport.

Foods Rich in Lipids

Butter, margarine, nuts, oils, lard, cheddar cheese, hamburger, salmon, eggs, avocado.

Cholesterol Source

Only present in animal foods.

Health Canada's Lipid Recommendations

Diet low in saturated fat, trans fat, and cholesterol; 20-35% of daily energy intake from lipids.

Fatty Acids

Simplest lipids containing methyl (non-polar) and carboxyl (polar) ends.

Fatty Acid Classification (Chain Size)

Short-chain (2-4 carbons), medium-chain (6-12 carbons), long-chain (14-26 carbons).

Fatty Acid Classification (Saturation)

Saturated (no double bonds) or unsaturated (presence of double covalent bonds).

Monounsaturated Fatty Acids (MUFA)

Fatty acids with one double bond (e.g., oleic and palmitoleic acids).

Polyunsaturated Fatty Acids (PUFAs)

Fatty acids with two or more double bonds (e.g., linoleic and arachidonic acids).

Numeric Representation of Fatty Acids

First number indicates the number of carbons, second the number of double bonds (e.g., 16:0 palmitic acid).

Delta (Δ) System for Double Bond Position

Counts carbons from the carboxyl end.

Omega (ω) System for Double Bond Position

Counts carbons from the methyl end.

Composition of Dietary Fats

Mix of polyunsaturated, monounsaturated, and saturated fatty acids in varied proportions.

Fatty Acid Solubility

Shorter fatty acids tend to be more water-soluble than longer ones; greater number of double bonds increases polarity and solubility.

Fatty Acid Melting Point

Greater chain length and more saturated a fatty acid is, the higher its melting point.

Essential Fatty Acids

Linoleic (18:2Δ9,12 ω-6) and α-linolenic (18:3Δ9,12,15 ω-3) acids are essential because humans lack Δ12 and Δ15 desaturases.

Consequences of Fat Abolishment

Retarded growth, dermatitis, kidney lesions, and early death.

Health Benefits of ω-3 Fatty Acids

Reduced blood pressure and blood clots, reduced risks of heart disease and stroke, and improved defense against inflammatory diseases.

Concerns with ω-6 Fatty Acids

Evidence suggests they can have a pro-inflammatory effect and be harmful.

Canadian Food Guide Recommendation for ω-3

Recommends two servings of fish a week, emphasizing fatty fish like salmon, herring, and mackerel (grilled, baked, or broiled).

Concerns with ω-3 Supplements

Can lead to excessive intake causing bleeding, interfere with wound healing, raise LDL, and suppress immune function.

Cis-fatty acids

Unsaturated fatty acids where hydrogens are located next to the double bond on the same side of the carbon chain

Trans-Fatty acids

Fatty acids where hydrogens next to the double bonds are on the opposite side of the carbon chain

Hydrogenation

Industry process to add hydrogens to unsaturated fatty acids, protecting against oxidation and prolonging shelf life but potentially creating trans fatty acids.

Health Risks of Trans-Fat

Increased LDL (bad cholesterol), lower HDL (good cholesterol), increased weight gain, promotes visceral fat accumulation, and induces inflammation.

Triglycerides (TG)

Composed of three fatty acids esterified to one glycerol molecule; found in salad dressing, butter, nuts, dairy products, bacon, beef, and skin of chicken.

Function of TGs in Adipose Tissue

Energy storage and thermal insulation.

Functions of TGs

Carriers of lipid soluble vitamins (A, D, E, K), confer taste to food, and signal for satiety.

Catabolism of TGs

Hydrolysis yields glycerol and three fatty acids.

Activation of Fatty Acids

Attachment of coenzyme A to form acyl-CoA, an irreversible reaction that consumes 2 ATPs.

Function of Carnitine

Carrier molecule for long-chain fatty acids to enter the mitochondrial matrix for β-oxidation.

Products of β-oxidation

Sequential cleavage in two-carbon units (acetyl-CoA) that enter the Krebs cycle.

ATP Production from Palmitate

Complete β-oxidation yields about 106 molecules of ATP.

ATP Production from Glucose

Complete catabolism yields 32 molecules of ATP.

Phospholipids

Composed of glycerol, two fatty acids, and a phosphate group (PO4); amphiphilic molecules.

Function of Phospholipids

Structural components for cellular membranes and lipoprotein shells.

Phospholipid Variants

Phosphatidylcholine (lecithin), phosphatidylethanolamine (cephalin), phosphatidylserine, and phosphatidylinositol.

Hydrophilic Property of Phospholipids

Commonly positioned on the surface of chylomicrons, helping stabilize the particle in an aqueous solution.

Function of Phospholipids in Membranes

Serve as conduits for passage of H2O and fat-soluble material across the membrane and provide compounds for eicosanoid synthesis and intracellular signaling.

Sterols

Lipids characterized by a four-ring core structure (cyclopentanoperhydrophenanthrene) or steroid nucleus.

Most Common Sterol in Animals

Cholesterol, which serves as a precursor for steroid molecules.

Liver's Role in Cholesterol

Liver cells make about 800 to 1500 mg of cholesterol every day and use it for bile production.

Catabolism and Elimination of Cholesterol

Occurs through the biliary system without energy production.

Phytosterols

Plant sterols that are poorly absorbed but can inhibit the absorption of cholesterol.

Endogenous Cholesterol Synthesis

Body can synthesize cholesterol, so it is not needed in the diet; it occurs mostly in the liver and intestine.

Precursor for Cholesterol Synthesis

Acetyl-CoA, derived from glucose, fatty acids, and amino acids.

Rate-Limiting Enzyme in Cholesterol Synthesis

Hydroxymethylglutaryl-CoA (HMG-CoA) reductase, inhibited by cholesterol.

Site of Lipid Digestion

It is in the intestine that most TGs are digested, and this requires bile salts and pancreatic lipase.

Lipid Hydrolysis

Salivation and mastication in the oral cavity allow lingual lipase to start hydrolyzing TGs and continues in the stomach with gastric lipase.

Function of Bile Salts

Cause emulsification of lipids so pancreatic lipase can gain access and hydrolyze ester bonds at the sn-1 and sn-3 positions of the glycerol moiety.

Function of Colipase

Binds lipase and reverses the inhibition by bile salts ensuring adhesion of lipase to the lipid droplet.

Products of TG Digestion

2-monoacyl-glycerols (2-MAGs) and free fatty acids. Other lipids such as phospholipids and cholesterol esters have their ester bonds cleaved by phospholipases and cholesterol esterase, respectively.

Micelles

Formed by the combination of lipids digestion products with bile salts, they are negatively charged aggregates that are small and water-soluble to access the enterocytes of the small intestine.

Absorption of Fatty Acids

Occurs in the distal duodenum and jejunum through protein-independent (diffusion) and protein-dependent mechanisms (FATP 1-4 and FAT/CD36). None of these processes require energy.

Synthesis in Enterocytes

LCFAs are converted to TGs and cholesterol to sterol esters in the reticulum endoplasm.

Enterohepatic Circulation

Process by which bile salts are reabsorbed in the terminal part of the ileum by an energy-requiring process and re-enter the portal vein for reuse by the liver.

Lipoproteins

Due to the hydrophobic nature of lipids, they are transported into the bloodstream as constituent of lipoproteins

Key Lipoproteins

Chylomicrons, VLDL, IDL, LDL, and HDL.

Chylomicrons

Lipoproteins produced by the enterocytes; made up of 90% TG, 55 Cholesterol, 4%% Phospholipids and 1% Protein.

VLDL

Lipoproteins produced by the liver; made up of 65% TG, 13% Cholesterol, 13% Phospholipids and 10% Protein.

LDL

Lipoproteins made up of made up of 10% TG, 45% Cholesterol, 23% Phospholipids and 20% Protein.

HDL

Lipoproteins made up of made up of 2% TG, 18% Cholesterol, 30% Phospholipids and 50% Protein.

Function of LDL

Deliver cholesterol to tissues where it may be used for membrane construction, as well as to produce steroid hormones

Function of HDL

Particle that removes unesterified cholesterol from the cells and other lipoproteins and transport them to the liver

PCSK9

Protein that regulates the clearance of LDL particles from the blood (clearance). When not tagged with PCSK9, LDLR bind LDL particles and form a complex that enters cell.

Proteins

Essential nutrients because they are critical components of all cells and tissues in our body. Proteins contribute to cell growth, repair and maintenance.

Protein Recommendation

Protein RDA is higher for children (0.85 to 1.52 g/kg/day) and women during pregnancy and lactation (1.1 g/kg/day) due to the higher demand for growth and development

Amino Acids

Molecules consist of polypeptides that grow longer and fold to take a variety of complex shapes and forms

Essential Amino Acids

Of the 20 amino acids, 9 our body cannot either synthesize at all or in sufficient amounts, so they are considered essential/indispensable amino acids and must be obtained from dietary sources.

Digestion of Proteins

Occurs mainly in the stomach and small intestine, since very little digestion of proteins occurs in the mouth and esophagus

Absorption

Several amino acid transporters are present across the apical and basolateral membranes of enterocytes. Amino acid transporters vary in their mechanism of action.

mRNA

Single strand molecule that carries the genetic information from the nucleus to the cytoplasm where translation occurs on ribosomes.

rRNA

Subcellular structures (RNA complexed with proteins) on which protein synthesis occur.

tRNA

Carries the amino acids to ribosomes and ensure that they are incorporated into the appropriate positions in the growing polypeptide chain.