Exam 2: Chapter 6, Lipids

Question 1

What are the three types of lipids?

Answer 1

Triglycerides, phospholipids, and sterols

Question 2

The most common type of lipid in food (about 95%). Also, the major form of lipid stored in our body.

Answer 2

Triglycerides

Question 3

Functions as a component of cell membranes and as an emulsifier.

Answer 3

phospholipids

Question 4

a type of steroid, cholesterol is the most well known.

Answer 4

sterols

Question 5

What is the structure of triglycerides, and how are they formed?

Answer 5

Structure: consists of 3 fatty acids attached to glycerol

Formation: Through a process called esterification (attaching fatty acids to glycerol’s hydroxyl groups)

• De-esterification
  
  • The release of fatty acids from glycerol
• Re-esterification
  
  • The process of reattaching a fatty acid to glycerol
• Diglyceride
  
  • A triglyceride that loses a fatty acid
• Monoglyceride
  
  • A triglyceride that has lost 2 fatty acids

Question 6

What are free fatty acids?

Answer 6

fatty acids that are unattached from the glycerol backbone.

• They are chains of carbons linked together and surrounded by hydrogens.
• They have an acid (carboxyl) group at one end of the chain and a methyl group at the opposite end.

Question 7

How do free fatty acids vary?

Answer 7

1. The number of carbons in the chain
2. The extent to which the chain is saturated with hydrogen
3. The shape of the chain (straight or bent)

Question 8

≥ 12 carbon atoms, fats from beef, pork, lamb and plant oils are long chain. These fatty acids are usually solid at room temperature.

Answer 8

Long chain fatty acids

Question 9

6-10 carbon atoms, fats from coconut and palm kernel oils are medium chain. Solid when chilled, but liquid at room temperature.

Answer 9

Medium chain fatty acids

Question 10

Less than 6 carbons in length, fats from dairy products like butter and whole milk are short chain. These fatty acids are usually liquid at room temperature.

Answer 10

Short chain fatty acids

Question 11

Every carbon in the chain has formed a maximum of 4 bonds and you have no double bonds

Answer 11

Saturated fatty acids (SFA)

Question 12

A fatty acid that has 1 double bond in the carbon chain

Answer 12

Monounsaturated fatty acids (MUFA)

Question 13

A fatty acid that has at least 2 double bonds in its carbon chain

Answer 13

Polyunsaturated fatty acids (PUFA)

Question 14

The shape of the carbon chain varies with saturation:

• Unsaturated cis fatty acids have carbon chains
• Trans and saturated fatty acids have carbon chains

Answer 14

• bent (kinked)
• straight

Question 15

What foods contain trans fatty acids?

Answer 15

crackers, chocolate chip cookies, biscuits, shortening, whole milk, margarine, ground beef, milk chocolate

Question 16

Trans fatty acids are formed through a process called , which causes some double bonds to become . Trans fatty acids have be shown to raise blood cholesterol levels and increase the risk of heart disease.

Answer 16

• hydrogenation
• saturated

Question 17

For naming fatty acids according to the omega system, what three things do you need to know?

Answer 17

1. Number of carbons in the fatty acid
2. Number of double bonds
3. Number of carbons from the methyl end (aka Omega end) to the first carbon in the double bond closest to the methyl end

Question 18

What are essential fatty acids?

Answer 18

Two polyunsaturated fatty acids in our diet that we must get from food, because our bodies are unable to make them.

They are:

1. Alpha-linolenic acid (the major omega-3 fatty acid in food)
2. Linoleic acid (the major omega-6 fatty acid in food)

Question 19

We also need essential fatty acids because…

Answer 19

they are are also used to make other important fatty acids; the Eicosanoids

Question 20

How do we identify hidden sources of fats?

Answer 20

• Fat is some foods is visible (i.e. butter on bread, mayonnaise in a deli salad)
• Fat in other foods are NOT visible (i.e. pastries, cookies, cakes, etc.)
• How do we identify the hidden sources of fat? Go to the Label!

Question 21

Functions of Triglycerides

Answer 21

1. Provide energy 9kcal/g
2. Main storage form of energy (storage amount is limitless!)
3. Insulates and protects the body (ex: subcutaneous fat is the layer of fat right beneath your skin, this is made mostly of triglycerides)
4. Aid fat-soluble vitamin absorption and transport (i.e. carry vitamins A, D, E and K from foods to the small intestine for absorption)
5. Essential fatty acid functions (important structural components of cell walls)

Question 22

What are characteristics of phospholipids?

Answer 22

1. Structure is very similar to a triglyceride except one fatty acid is replaced with phosphate instead
2. Phosphate allows phospholipids to function in a watery environment (ex: the blood) without clumping together
3. Hydrophillic and hydrophobic ends

Question 23

Function and sources of phospholipids

Answer 23

Functions:

1. Components of cell membranes
2. Emulsifiers (e.x: bile and lecithins)

Sources:

• Can be synthesized by the body or supplied by the diet
• Food: egg yolks, wheat germ and peanuts

Question 24

Functions and sources of sterols

Answer 24

Functions:

•Produces steroid hormones, bile, cell membranes, lipoprotein shell (e.g., chylomicrons)

Sources:

1. Synthesized by the body
2. Found in foods of animal origin (meat, fish and poultry)
3. Foods of plant origin do not contain cholesterol, but plants produce other sterols like ergosterol (a form of Vitamin D)

Question 25

RDA for fats

Answer 25

There is no RDA for fats.

Question 26

AMDR for fats

Answer 26

20-35% of calories for most age groups

Question 27

2010 Dietary guidelines for fats

Answer 27

Limit saturated and trans fat

Question 28

American Heart Association recommendations for those at risk for heart disease:

Answer 28

• Limit saturated fats to 7% of total calories
• Limit cholesterol intake to less than 200 mg

Question 29

What is the Mediterranean Diet?

Answer 29

• Up to 40% kcal from fat is healthy if mostly MUFA
• Traditional diet features:
  
  • Olive oil as main fat
  • Abundant fruits & vegetables, whole grains, beans, nuts, and seeds
  • Daily intake of small amounts of cheese and yogurt
  • Weekly fish intake; limited use of eggs and red meat
  • Regular exercise and rest
  • Moderate drinking of wine at mealtime

Question 30

Essential Fatty Acid Needs:

Answer 30

• IOM has set Adequate Intakes for essential fatty acids
  
  • Approximately 2-4 tablespoons daily of oils rich in these fatty acids
  • Deficiency is unlikely, but insufficient intake can lead to delayed wound healing, flaky itchy skin, etc.
• Toxicity
  
  • No Upper Level set

Question 31

Trace the general path of digestion and absorption of lipids

Answer 31

Question 32

Digestion and absorption of lipids: Mouth

Answer 32

Lingual lipase is secreted here, little or no fat is digested

Question 33

Digestion and absorption of lipids: Stomach

Answer 33

Gastric lipase is secreted, which helps break down triglycerides into monoglycerides, digylcerides and free fatty acids.

Question 34

Digestion and absorption of lipids: Small Intestine (Most fat digestion occurs here!)

Answer 34

1. The presence of fat in the S.I. triggers the release of CCK
2. CCK triggers the release of bile from the gallbladder and lipase + colipase from the pancreas
3. Bile emulsifies fat → micelles are formed → emulsification occurs, and this increases the surface area of lipids
4. Pancreatic lipase acts to breakdown TGs into monoglycerides and free fatty acids.
5. Phospholipids and cholesterol are also digested mostly in the S.I.
   * Phospholipids are broken down into their basic parts: free fatty acids, glycerol and phosphoric acid
   * Cholesterol esters are broken down into cholesterol and free fatty acids by an enzyme called cholesterol esterase

Question 35

The of a fatty acid or monoglyceride determines whether it is absorbed by the cardiovascular or the lymphatic system.

• short and medium chain fatty acids enter…
• long chain fatty acids enter…

Answer 35

chain length

• Short- and medium-chain fatty acids (<12 carbons) enter the cardiovascular system via the portal vein
• Long chain fatty acids (≥12 carbons) are re-esterified and enter the lymphatic system along with fat-soluble vitamins and dietary cholesterol

Question 36

Bile is recycled via (meaning that bile is reabsorbed in the ileum and returned to the liver to be used again)

Answer 36

enterohepatic circulation

Question 37

Question 38

How do we transport fat in the blood?

Answer 38

• Transporting fats through the water-based blood and lymphatic system presents a challenge because water and fat do not mix!
• Fat is transported in the blood as lipoproteins

Question 39

What are the different types of lipoproteins and what are their primary components?

Answer 39

• Chylomicrons
• very-low density lipoproteins
• intermediate-density lipoproteins
• low-density lipoproteins
• high-density lipoproteins

Composition of lipoprotein:

• Lipid core
• Shell composed of proteins, phospholipids, and cholesterol

Question 40

Lipoproteins:

Transport of dietary triglycerides;

(carries dietary fat from the small intestine to the cells)

Answer 40

Chylomicrons

Question 41

Lipoproteins:

Produced by liver; release triglycerides;

(carries lipids both taken up and made by the liver to the cells)

Answer 41

VLDLs

Question 42

Lipoproteins:

Formed from VLDL

Answer 42

IDLs

Question 43

Lipoproteins:

Formed from IDL; contain mostly cholesterol;

(carries cholesterol made by the liver and from other sources to the cells)

Answer 43

LDLs

Question 44

Lipoproteins:

Pick up and recycle or dispose of cholesterol;

(helps remove cholesterol from cells and, in turn, excretion of cholesterol from the body)

Answer 44

HDLs

Question 45

Receptor Pathway for Cholesterol Uptake

Answer 45

1. LDL is removed from the blood by cells with the LDL receptor called B-100. The liver as well as other cells have this receptor
2. Once inside the cell, LDL is broken down to protein and free cholesterol
3. When the free cholesterol concentration inside the cell increases to the point in which the cell can’t take up anymore LDL, the B-100 receptor stops.
4. As a result, the LDL concentration increases in the blood and can become oxidized

Question 46

Scavenger Pathway

Answer 46

1. Any oxidized LDL is removed from circulation by “scavengers” known as white blood cells in this pathway
2. The scavenger cells detect oxidized LDL, then engulf and digest it. Once engulfed, oxidized LDL is prevented from reentering the bloodstream.
3. Cholesterol buildup is problematic to scavenger cells. Cholesterol kills scavenger cells and build up on the inner blood vessels-especially the arteries and plaque develops.
4. Over time, the arteries harden and atherosclerosis develops.

Question 47

HDL helps remove cholesterol from cells and in turn, excretes cholesterol from the body

How does HDL do this?

Answer 47

1. HDL roams the bloodstream, picking up cholesterol from dying cells and other sources
2. HDL then donates cholesterol to other lipoproteins for transport back to the liver to be excreted
3. High amounts of HDL slow the development of CVD risk, it is your “GOOD” cholesterol

Question 48

Excessive omega-3 fat intake:

Answer 48

(4 to 8 ounces/day) may impair the function of the immune system and cause hemorrhagic stroke (usually the result of supplement use)

Question 49

Intake of rancid (spoiled) fats:

Answer 49

Spoiled fats contain peroxides and aldehydes that can damage cells. PUFAs are more likely to go rancid when compared to saturated or trans fats

Question 50

Diets high in trans fats:

Answer 50

Trans fats raise blood cholesterol levels, which increases the risk for heart disease. FDA now requires trans fats to be labeled. Foods that are trans fat free have less than 0.5g per serving