Lecture 4 Flashcards
What are the fat soluble vitamins?
A, D, E and K
What is fat made up of, as are carbohydrates and protein?
C, H, and O
Define lipids
A family of organic compounds that are not soluble in water.
What are the three categories of lipids?
Triglycerides (fats and oils)
Phospholipids (e.g., lecithin)
Sterols (e.g., cholesterol)
Which category makes up 95% of all lipids in foods & the human body?
Triglycerides
Triglycerides are made up of fats and oils. Define these two
Fats: lipids that are solid at room temperature
Oils: lipids that are liquid at room temperature
What are the functions of fat?
- Body’s chief storage form for excess food energy (glycogen is very bulky – way too much water, whereas fat is very energy-dense, so in a small weight can store lots of energy)
- Provides much of the energy needed for the body’s work (energy when a person becomes ill & stops eating)
Only limited fat storage is possible for most body cells. But, what are the cells specialized for fat storage called?
Adipose cells
How is adipose tissue active?
Secretes hormones and produces enzymes that influence food intake & affect the body’s use of nutrients
What are some other functions of fat?
- Shock absorbers (pads of fat surround vital internal organs)
- Thermoregulation (fat pads under the skin insulate the body from temperature extremes)
- Cell membranes (lipids are a component of cell membranes)
Fat-soluble vitamins are found mainly in what types of foods?
Foods that contain fat
Why do people naturally like high-fat foods?
- Fats carry many compounds that give foods pleasant aromas and flavours
- Fat makes meat and baked good tender
Fat contributes to satiety. What is that?
Feeling of fullness or satisfaction that people experience after meals.
The fat in the food triggers a series of physiological events that slow the emptying of the stomach & promote satiety.
How does fat contribute to the feeling of fullness and satisfaction?
Fat in the small intestine signals release of CCK (aids in digestion and reduces appetite)
What are triglycerides made up of?
3 fatty acids + glycerol
What are fatty acids?
Organic acids composed of carbon chains of various lengths. Each has an acid end & hydrogens attached to all of the carbon atoms of the chain. Differ on the basis of length & degree of saturation.
What is the backbone for triglycerides?
Glycerol
How does the degree of saturation relate to a food’s solidity?
Affects melting temperature:
- The more saturated, the more solid at room temperature
- The more unsaturated, the more liquid at room temperature
Fatty acid chains of what length are most common in the diet? And where are they found?
Long chain fatty acids (12 to 24 carbons)
Found in meat , seafood, and vegetable oils
Medium chain fatty acids are of what length? Where are they found mainly?
6 to 10 carbons
Short (less than 6)
Found in mainly dairy products
How is the length of carbon chains associated with the firmness of fats?
Lower carbon chain length leads to lower firmness
What are the health recommendations related to firmness of fats?
Limit saturated fats and limit/avoid trans fats
Using monounsaturated fats or polyunsaturated fats instead
Where do you find fats that are rich in polyunsaturated fatty acids?
Safflower, sunflower, corn oil
OIive oil is rich in what?
Polyunsaturated fatty acids
Which types of fats are generally the most saturated?
Animal fats and tropical fats
Fatty meats: Over 1/3 of the fat in most meats is saturated
Whole-milk products: Over 1/2 of the fat in whole milk & other high-fat dairy products, is saturated
Coconut & palm oils: Mostly used in commercially prepared foods
Evidence from Mediterranean regions suggests olive oil offers what?
A degree of protection against heart disease when it is used in place of other fats
Dark-coloured olive oils deliver more phytochemicals
What can be said about canola oil?
It is rich in both monounsaturated & polyunsaturated fatty acids
It is lowest in saturated fat
What is hydrogenation?
A chemical process by which hydrogens are added to monounsaturated or polyunsaturated fatty acids to reduce the number of double bonds, making the fats more saturated (solid) and more resistant to oxidation
How are trans fats formed?
A polyunsaturated fat is rarely hydrogenated completely during processing. Fat is generally partially hydrogenated, so double bonds remain
These double bonds change from the cis to the trans formation
No longer allowed to add partially hydrogenated food to our diets in Canada due to the negative effects on health
A small amount of trans fats are found naturally in what?
Milk and meat products
What are the advantages of hydrogenation (3)?
- Protects against oxidation by making polyunsaturated fats more saturated. Commerical benefit: longer shelf life
- Alters the texture of food by making liquid vegetable oils more solid. Commercial benefit: improved food texture (shortening – flaky pie crust, spreadable margarine, creamy pudding)
- Hydrogenated oil has a higher smoke point – more stable in high cooking temperatures
What are phospholipids made up of? And what can be said about its solubility?
2 fatty acids + glycerol + a phosphorus-containing molecule.
Fatty acid is soluble in fat and phosphorus is soluble in water
Phospholipids are emulsifiers. What does that mean?
It is a substance that mixes with both fat & water & disperses the fat in the water, forming an emulsion
What key roles do phospholipids play?
- In the structure of cell membranes
- Phospholipids help fats travel back & forth across the lipid-containing membranes of cells into the watery fluids on both sides.
What is a common phospholipid and where can you find it?
Lecithin
Eggs & peanuts
What are sterols made of?
Large molecules consisting of interconnected rings of carbon atoms with side chains of carbon, hydrogen & oxygen
Sterols are present in foods derived from both plants and animals. What are the two categories of sterols?
Cholesterol (only food derived from anumals contain significant amounts of cholesterol)
Phytosterols (plant sterols that have structural similarities to cholesterol, lower blood cholesterol by competing with cholesterol for absorption).
Cholesterol (a sterol) serves as the precursor for making what?
Bile, which is an emulsifier made by the liver & stored in the gallbladder.
Does bile digest fats?
No. Enzymes do. It emulsified fats allowing contact with enzymes in watery fluids to split the fatty acids from the glycerol backbone for absorption.
What else are sterols?
Vitamin D and sex hormones (e.g., estrogen and progesterone)
What are some characteristics of cholesterol?
- Component of cell membranes
- Can be made by the body (not essential, manufactured in the liver, the body generally makes more cholesterol than what is eaten)
- Forms a major part of the plaques that narrow arteries in atherosclerosis
How does cholesterol lead to plaque which is often the cause of heart attacks and strokes?
Either narrow it down until they completely block off the artery, or for a stroke, a piece of this plaque may break off and travel throughout the blood vessels until it reaches a small blood vessel in the brain & blocks it off
How are fats digested in the mouth?
Lingual lipase produced by the tongue acts on triglycerides with short and medium chain fatty acids (plays a major role in infants, little importance to digestion in adults)
How are fats digested in the stomach?
Strong and muscular – mix fat with other stomach contents.
Churning grinds the solid pieces into finer particles, and disperses the fat into small droplets
Gastric lipase begins to break down triglycerides. Works best in the acidic environment of the stomach.
How are fats digested in the small intestine?
When fat enters the small intestine, bile is secreted (in response to CCK)
Bile emulsifies fat particles – mixing them with watery fluid for contact with enzymes for digestion
Then the emulsified fat particles are acted on by fat-digesting enzymes secreted by the pancreas.
What happens if someone’s gallbladder has been removed?
Liver still produces bile – small continuous amount in small intestine
They can no longer store bile & release it at mealtime