Nutrition: The Lipids - Triglycerides, Phospholipids, and Sterols

Comprehensive vocabulary flashcards covering the chemistry, structures, digestion, absorption, transport, and physiological roles of triglycerides, fatty acids, phospholipids, sterols, and lipoproteins.

Triglyceride

The predominant lipid molecule in both foods and the human body, composed of one molecule of glycerol bonded to three fatty acids.

Fatty Acid

An organic compound consisting of a carbon and hydrogen chain with an acid group ($\text{COOH}$) at one end and a methyl group ($\text{CH}_3$) at the other end.

Saturated Fatty Acid

A fatty acid that is fully loaded with hydrogen atoms and contains only single bonds between its carbon atoms.

Unsaturated Fatty Acid

A fatty acid that is missing hydrogen atoms and contains at least one carbon-to-carbon double bond, which serves as a point of unsaturation.

Monounsaturated Fatty Acid

A fatty acid that possesses exactly one carbon-to-carbon double bond in its chain, such as oleic acid.

Polyunsaturated Fatty Acid (PUFA)

A fatty acid containing two or more carbon-to-carbon double bonds in its carbon chain, such as linoleic acid and linolenic acid.

Stearic Acid

An 18-carbon saturated fatty acid containing zero double bonds, commonly found in most animal fats.

Oleic Acid

An 18-carbon monounsaturated fatty acid with one double bond, abundant in olive oil and canola oil.

Linoleic Acid

An 18-carbon essential polyunsaturated omega-6 fatty acid with two double bonds, commonly found in sunflower, safflower, corn, and soybean oils.

Linolenic Acid

An 18-carbon essential polyunsaturated omega-3 fatty acid with three double bonds, found in soybean oil, canola oil, flaxseed, and walnuts.

Omega Number

A naming convention identifying the position of the double bond closest to the methyl ($\text{CH}_3$) end of a polyunsaturated fatty acid.

Essential Fatty Acids

Fatty acids that the human body cannot synthesize from scratch or convert from other fatty acids, specifically linoleic acid (omega-6) and linolenic acid (omega-3).

Long-Chain Fatty Acids

Fatty acids containing more than $12$ carbons in length, which are the most common fatty acids found in meats, seafood, and vegetable oils.

Medium-Chain Fatty Acids

Fatty acids containing $8$ to $12$ carbons, occurring primarily in dairy products.

Short-Chain Fatty Acids

Fatty acids containing up to $6$ carbons in length, occurring primarily in dairy products.

Intermolecular Forces (in Fats)

Forces holding molecules together that are stronger in long-chain fats than in short-chain fats, explaining why longer-chain fats are firmer and have higher melting points at room temperature.

Rancidity

The spoilage of fats caused by oxidation upon exposure to oxygen, heat, or light, producing off-flavors and odors; polyunsaturated fats are the most susceptible.

Hydrogenation

A commercial process where hydrogen atoms are added to unsaturated fats to saturate points of unsaturation, prolonging shelf life and making liquid vegetable oils more solid.

Cis-Fatty Acids

Naturally occurring unsaturated fatty acids in which the hydrogen atoms adjacent to the double bond are positioned on the same side of the carbon chain.

Trans-Fatty Acids

Fatty acids where hydrogen atoms adjacent to the double bond are situated on opposite sides of the chain; they behave biologically like saturated fats, elevating blood cholesterol and heart disease risk.

Phospholipid

A compound similar to a triglyceride but having one molecule of glycerol attached to two fatty acids, with the third site occupied by a phosphate group and a choline molecule.

Lecithin

The most well-known phospholipid, rich in eggs, liver, soybeans, wheat germ, and peanuts, which serves as an emulsifier and a precursor to the neurotransmitter acetylcholine.

Emulsifier

A substance possessing both hydrophilic and hydrophobic properties, enabling fats to remain suspended in water-based solutions such as blood and body fluids.

Sterols

Compounds with a four-ring carbon structure and a carbon side chain, found in plant and animal foods, which cannot be metabolized to generate energy.

Cholesterol

The best-known sterol, found exclusively in animal-derived foods, that acts as a structural component of cell membranes and a precursor for steroid hormones, vitamin D, and bile.

Endogenous Cholesterol

Cholesterol produced within the body, primarily synthesized by the liver at a rate of $800\text{ to }1500\,\text{mg/day}$ from fragments of carbohydrate, protein, and fat.

Exogenous Cholesterol

Cholesterol obtained from external sources through the consumption of animal products such as meat, poultry, seafood, eggs, and dairy.

Atherosclerosis

A cardiovascular disease caused by the buildup of cholesterol-rich plaque deposits inside arterial walls, leading to heart attacks and strokes.

Lingual Lipase

A fat-digesting enzyme released by a sublingual salivary gland at the base of the tongue that plays an active digestive role on milk fats in infants and a minor role in adults.

Gastric Lipase

An enzyme active in the acidic environment of the stomach that hydrolyzes a very small fraction of fat exposed during stomach churning.

Cholecystokinin (CCK)

A hormone triggered by fat entering the small intestine that signals the gallbladder to release bile into the duodenum.

Bile Acids

Compounds synthesized in the liver from cholesterol and stored in the gallbladder, featuring a hydrophilic amino acid end and a hydrophobic sterol end that emulsify fats.

Pancreatic Lipase

The principal fat-digesting enzyme in the small intestine that removes outer fatty acids from triglycerides one at a time, producing monoglycerides and free fatty acids.

Micelles

Water-soluble complexes formed by bile salts, monoglycerides, and long-chain fatty acids that facilitate the diffusion of lipid components across the intestinal absorptive cells.

Lipoprotein Density Rule

The physiological principle stating that the more lipids a lipoprotein contains, the less dense it is; conversely, the more proteins it contains, the more dense it is.

Chylomicrons

The largest and least dense lipoproteins, which transport diet-derived lipids (mostly triglycerides) from the intestinal cells via the lymphatic system to the rest of the body.

Very-Low-Density Lipoproteins (VLDL)

Lipoproteins assembled by the liver from endogenous lipids and chylomicron remnants to deliver triglycerides and other lipids to peripheral body tissues.

Low-Density Lipoproteins (LDL)

Cholesterol-rich lipoproteins derived from VLDL as cells remove lipids, responsible for supplying cholesterol, triglycerides, and phospholipids to peripheral tissues.

High-Density Lipoproteins (HDL)

Dense lipoproteins synthesized by the liver to transport excess cholesterol from peripheral cells back to the liver for recycling or disposal, providing anti-inflammatory benefits.

Adipokines

Biologically active hormones secreted by the fat cells of adipose tissue that help regulate body functions and energy balance.