[NUTR 110] Chapter 5: Lipids (Fats, Phospholipids, and Sterols)

adipose tissue

Tissue found under the skin and around body organs that is composed of fat-storing cells called adipocytes.

alpha-linolenic acid (α-linolenic acid)

An 18-carbon omega-3 polyunsaturated fatty acid known to be a dietary essential in humans.

antioxidant

A substance that decreases the adverse effects of reactive molecules on normal physiological function.

arachidonic acid

A 20-carbon omega-6 polyunsaturated fatty acid that can be synthesized from linoleic acid.

atherosclerosis

A type of cardiovascular disease that involves the buildup of fatty material in the artery walls.

atherosclerotic plaque

Cholesterol-rich material that is deposited in the arteries of individuals with atherosclerosis.

cardiovascular disease

Any disease affecting the heart and blood vessels.

Number 1 cause of death for both men and women in the United States.

cholesterol

A sterol, produced by the liver and consumed in the diet, which is needed to build cell membranes and synthesize hormones and other essential molecules. High blood levels increase the risk of heart disease.

chylomicron

A lipoprotein that transports lipids from the mucosal cells of the small intestine and delivers triglycerides to other body cells.

→ transport triglycerides

docosahexaenoic acid (DHA)

A 22-carbon omega-3 polyunsaturated fatty acid found in fish that may be needed in the diet of newborns. It can be synthesized from α-linolenic acid.

eicosanoids

Regulatory molecules that can be synthesized from omega-3 and omega-6 fatty acids.

hormone like molecules made from omega-3 and omega-6 polyunsaturated fatty acids. Help regulated blood clotting, blood pressure, immune function, and other body processes.

Want to make our eicosanoids from Omega-3 because they decrease more inflammation, blood clotting, and blood pressure. Omega-6 derived eicosanoids increase inflammation, blood clotting, and blood pressure.

Increasing consumption of foods rich in omega-3 fatty acids increases the proportion of omega-3 eicosanoids. This reduces the risk of heart disease by decreasing inflammation, lowering blood pressure, and reducing blood clotting.

fat as a source of energy

Depositing fat in adipose tissue is an efficient way to store energy. Each gram of fat provides 9 Calories.

Feasting: consuming more calories than needed. The excess is stored primarily as fat.

Fasting: consuming fewer calories than needed. An enzyme inside of fat cells receives a signal to break down stored triglycerides. The fatty acids and glycerol are released directly into the blood and circulate throughout the body.

eicosapentaenoic acid (EPA)

A 20-carbon omega-3 polyunsaturated fatty acid found in fish that can be synthesized from α-linolenic acid but may be essential in humans under some conditions.

emulsifier

A substance containing both water-soluble and fat-soluble portions that allows one liquid to be suspended in another, as in the mixture of oil and water.

essential fatty acid

A fatty acid that must be consumed in the diet because it cannot be made by the body or cannot be made in sufficient quantities to meet the body's needs.

The body can make all but two:

Linoleic (omega-6). Found in vegetable oils such as corn and safflower oil.
- Arachidonic acid: synthesized from linoleic acid; found in both animal and plant fats
- Examples: corn oil, safflower oil, soybean oil, nuts

Alpha-linolenic (omega-3). Found in nuts, flaxseed, and canola oil.
- Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA); synthesized from alpha-linolenic acid
- Examples: flaxseeds and flaxseed oils, walnuts, fish oil, canola oil, fatty fish

Omega-6 to Omega-3 ratio: Between 5:1 to 10:1 of omega-6 to omega-3 fatty acids.

essential fatty acid deficiency

A condition characterized by dry, scaly skin and poor growth that results when the diet does not supply sufficient amounts of linoleic acid and α-linolenic acid.

fat

The typical American diet is made up of ~35% _____.

fatty acid

A molecule made up of a chain of carbons linked to hydrogens, with an acid group at one end of the chain.
Their bonds and locations determine the function of the triglyceride in the body and the properties it has in food.
- short chain: 4-7 carbons
- medium chain: 8-12 carbons
- long chain: more than 12 carbons

most plants and animals: 14-22 carbons

Fatty acids can differ from one another in 3 ways: **EXAM**
(1) length of chain
(2) types of bonds
(3) location of bonds

foam cell

A cholesterol-filled white blood cell named for its foamy appearance under a microscope.

high-density lipoprotein (HDL)

A lipoprotein that picks up cholesterol from cells and transports it to the liver so that it can be eliminated from the body.

→ transport cholesterol OUT of the body

lipid functions

Diet: fat is needed to absorb fat-soluble vitamins; it is a source of essential fatty acids and energy.

In the body: lipids form structural and regulatory molecules and are broken down to provide ATP (energy).

Triglycerides found in oils lubricate body surfaces, keeping the skin soft and supple.

Adipose tissue: the primary storage form of triglyceride in the body, cushions our internal organs, and insulates the body from changes in temperature.

The amount and location of adipose tissue affect body size and shape.

Cells contain large droplets of triglyceride. As weight is gained, the triglyceride droplets enlarge.

When we lose weight, adipocytes decrease in size (you don't lose fat cells)

hydrogenation

A process used to make partially hydrogenated oils in which hydrogen atoms are added to the carbon-carbon double bonds of unsaturated fatty acids, making them more saturated. Trans fatty acids are formed during the process.

Trans Fat vs Palm Oil:
trans fat increases the risk of heart disease → now palm oil is now being used
There are several problems with palm oil → increased saturated fat consumption → environmental issues with palm oil production

LDL receptor

A protein on the surface of some body cells that binds to LDL particles and transports them into the cells, removing them from the blood.

lecithin

A phosphoglyceride composed of a glycerol backbone, two fatty acids, a phosphate group, and a molecule of choline; often used as an emulsifier in foods.

linoleic acid

An omega-6 essential fatty acid with 18 carbons and 2 carbon-carbon double bonds.

lipid

A class of nutrients, commonly called fats, that includes saturated and unsaturated fats, phospholipids, and cholesterol; most do not dissolve in water.

lipid bilayer

Two layers of phosphoglyceride molecules oriented so that the fat-soluble fatty acid tails are sandwiched between the water-soluble phosphate-containing heads.

lipoprotein

A particle that transports lipids in the blood.

A lipoprotein consists of a core of triglycerides and cholesterol surrounded by a shell of protein, phospholipids, and cholesterol.

Phospholipids orient with their fat-soluble "tails" toward the interior and their water-soluble "heads" toward the outside.

This allows fat-soluble substances in the interior to travel through aqueous blood.

Four Types
(1) Chylomicrons: The largest lipoprotein and contain the greatest proportion of triglycerides. → transport triglycerides

(2) Very-low-density lipoproteins (VLDL): Smaller than chylomicrons but still contain a high proportion of triglycerides. → transport triglycerides

(3) Low-density lipoproteins (LDL): Contain a higher proportion of cholesterol than do other lipoproteins. → transport cholesterol into the body

(4) High-density lipoproteins (HDL): High in cholesterol and are the densest lipoproteins due to their high protein content. → transport cholesterol out of the body

lipoprotein lipase

An enzyme that breaks down triglycerides into free fatty acids and glycerol; attached to the outside of the cells that line the blood vessels.

low-density lipoprotein (LDL)

A lipoprotein that transports cholesterol to cells.

→ transport cholesterol INTO the body

macrophage

A type of white blood cell that ingests foreign material as part of the immune response to foreign invaders such as infectious microorganisms.

micelle

A particle that is formed in the small intestine when the products of fat digestion are surrounded by bile acids. It facilitates the absorption of lipids.

monoglyceride

A glycerol molecule with one fatty acid attached.

monounsaturated fatty acid

A fatty acid containing one carbon-carbon double bond.

Examples: canola, olive oil, nuts, avocados

omega-3 fatty acid

A fatty acid containing a carbon-carbon double bond between the third and fourth carbons from the omega end; includes α-linolenic acid found in vegetable oils and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) found in fish oils.

DHA important for retina of eye.

omega-6 fatty acid

A fatty acid containing a carbon-carbon double bond between the sixth and seventh carbons from the omega end; includes linoleic and arachidonic acid.

Important for brain development and cell membranes

oxidation

A chemical reaction in which a substance loses electrons.

oxidized LDL cholesterol

A harmful type of cholesterol that is formed in the arteries when cholesterol in LDL particles is chemically modified by reactive oxygen molecules.

partially hydrogenated oil

Liquid oils that have undergone a process that adds hydrogen atoms to the carbon-carbon double bonds of unsaturated fatty acids to make the oil more solid and/or increase the shelf life of the product.

phosphate group

A chemical group consisting of one phosphorus atom and four oxygen atoms.

phospholipid

A type of lipid whose structure includes a phosphorus atom.

Fatty acids at one end of the molecule are soluble in fat.
The phosphate-containing group is soluble in water.

Can act as emulsifiers.
Emulsifiers allow fat and water to mix.

Lecithin is a phospholipid. Sources: eggs and soybeans

The food industry uses lecithin as an emulsifier in: dressings, etc.

In the body, lecithin is a major constituent of cell membranes.
Phospholipids are an important component of cell membranes.

plant sterol

A compound found in plant cell membranes that resembles cholesterol in structure. It can lower blood cholesterol by competing with cholesterol for absorption in the gastrointestinal tract.

polyunsaturated fatty acid

A fatty acid that contains two or more carbon-carbon double bonds.

Examples
Walnuts.
Sunflower seeds.
Flax seeds or flax oil.
Fish, such as salmon, mackerel, herring, albacore tuna, and trout.
Corn oil.
Soybean oil.
Safflower oil.

saturated fat

A type of lipid that is most abundant in solid animal fats and is associated with an increased risk of heart disease.

saturated fatty acid

A fatty acid in which the carbon atoms are bonded to as many hydrogen atoms as possible; it therefore contains no carbon-carbon double bonds.

Straight chains, closely packed together

Highly stable, unlikely to become rancid

Shown to increase the risk of heart disease → try to limit in the diet

Triglycerides high in saturated fatty acids are solid at room temperature.

Examples: butter, fat on meat, coconut oil

Animal fats and tropical (coconut and palm) oils are high in saturated fatty acids.

rancidity

fats become rancid when exposed to oxygen

Saturated fats are the most chemically stable and therefore do not become rancid as quickly as unsaturated fatty acids which are more vulnerable due to their double bonds.

sterol

A type of lipid with a structure composed of multiple chemical rings.

Cholesterol is the best-known sterol. It is not essential because the body manufactures it in the liver.

More than 90% of the cholesterol in the body is found in cell membranes.

Also part of the myelin on many nerve cells.

Cholesterol is needed to synthesize other sterols, including Vitamin D.

Cholesterol is found only in foods from animal sources.

It is used to make cell membranes, myelin (nerve coatings), Vitamin D, bile acids, cortisol, testosterone, and estrogen

Plant sterols help form plant cell membranes. Found in small quantities in most plant foods.

When consumed in the diet, helps to reduce cholesterol levels in the body.

digestion and absorption of fat

Small Intestine - The liver produces bile, which is stored in the gallbladder and released into the small intestine. The pancreas produces the enzyme pancreatic lipase, which is released into the small intestine to break down triglycerides into monoglycerides, fatty acids, and glycerol. In the small intestine, the products of fat digestions and bile form micelles, which allow lipids to diffuse into the mucosal cells.
Inside the mucosal cells, fatty acids and monoglycerides are reassembled into triglycerides and incorporated into lipid transport particles, which enter the lymph.
Fat absorption in the small intestine is efficient. Little fat is lost in the feces.
Bile acts an emulsifier, breaking down large lipid droplets into small globules.
The triglycerides in the globules can then be digested by enzymes from the pancreas.
The resulting mixture of fatty acids, monoglycerides, cholesterol, and bile forms smaller droplets called micelles, which facilitate absorption.
The bile in the micelles is also absorbed and returned to the liver to be reused.
Once inside the mucosal cells of the intestine, the fatty acids, cholesterol, and other fat-soluble substances must be further process before they can be transported in the blood.

Fat-soluble vitamins - Vitamins A, D, E, K
- Absorbed the same way as other lipids
- Are not digested but must be incorporated into micelles to be absorbed

transporting lipids in the blood

Lipoprotein: Transports lipids from the small intestine and liver to body cells, from body cells back to the liver for disposal

Different types of lipoproteins transport dietary lipids from the small intestine to body cells, from the liver to body cells, and from body cells back to the liver for disposal.

Short and medium-chain fatty acids are soluble in water and can be transported in the blood unaltered

Long-chain fatty acids, cholesterol, and fat-soluble vitamins (A, D, E, K) must be specially...

trans fat

A term used to refer to triglycerides containing trans fatty acids. When consumed in the diet these fats increase the risk of heart disease.

trans fatty acid

An unsaturated fatty acid in which the hydrogens are on opposite sides of the carbon-carbon double bond.

triglyceride

The major type of lipid in food and the body, consisting of three fatty acids attached to a glycerol molecule.

When we use the word fat, we generally mean the lipid _____.

Make up the majority of lipids in or bodies

Made up a 3 carbon molecule of glycerol and 3 fatty acids

tropical oil

A term used in the popular press to refer to the saturated plant oils—coconut, palm, and palm kernel oil—that are derived from plants grown in tropical regions.

unsaturated fat

A type of lipid that is most abundant in plant oils and is associated with a reduced risk of heart disease.

unsaturated fatty acid

A fatty acid that contains one or more carbon-carbon double bonds; may be either monounsaturated or polyunsaturated.

Do not contain the maximum number of hydrogens. They contain at least one double bond between the carbons of the carbon chain.

Bent carbon chains, prevent tight packing allowing oils to "flow"

Triglycerides high in unsaturated fatty acids are liquid at room temperature.

Monounsaturated fatty acid: contain 1 double bond in the carbon chain. Examples: canola, olive oil, nuts, avocados

Polyunsaturated fatty acid: two or more double bonds in the carbon chain.

Plant foods are generally high in unsaturated fatty acids.

very-low-density lipoprotein (VLDL)

A lipoprotein assembled by the liver that carries lipids from the liver and delivers triglycerides to body cells.

→ transport triglycerides