Unit 5: Lipids; Fats, Oils, Phospholipids, And Sterols Flashcards
Define Lipids
Organic compounds composed of primarily carbon, hydrogen and small amounts of oxygen.
Insoluble in water but soluble in organic solvents
Triglycerides include:
Fats that are usually solid at room temperature
Oils that are usually liquid at room temperature
Make up 95% of dietary lipids
Make up 99% of stored fat in the body
5% of dietary lipids are made up of:
Phospholipids, sterols, fat-soluble vitamins, waxes and other minor complex lipid compounds
Define Fatty Acid
An organic compound composed of a carbon chain with hydrogens attached and an acid group (COOH) at one end and a methyl group (CH3) at the other end. The building blocks of lipids
How many carbons does a short-chain fatty acid have?
Less than 6 carbons
How many carbons does a medium-chain fatty acid have?
6-10 carbons
How many carbons does a long-chain fatty acid have?
12-4 carbons
How many double bonds does a Saturated Fatty acid (SFA) have?
No double bonds
Most possible number of hydrogens
Ex. Stearic Acid
How many double bonds does a Monounsaturated Fatty Acid (MUFA) have?
1 double bond
Lacks 2 hydrogens
Ex. Leicester Acid
Monounsaturated oil or fat is composed of triglycerides in which most of the fatty acids are monounsaturated
How many double bonds does a Polyunsaturated Fatty Acid (PUFA) have?
2 or more double bonds
Lacks 4 or more hydrogens
Ex. Linoleic acid
Polyunsaturated fat or oil is composed of triglycerides in which most of the fatty acids are polyunsaturated
Define Point of Unsaturation
The double bond of a fatty acid, where hydrogen atoms can be easily added to the structure
Define Omega-3 Fatty Acid
Polyunsaturated fatty acid with its first double bond 2 carbons from the methyl end
Define Omega-6 Fatty Acid
Fatty Acid with its first double bond 6 carbons from the methyl end
Monounsaturated fatty acids tend to belong to what group. Because their first (an only) double bond is 9 carbons from the methyl end.
Omega-9 group
Chemists identify polyunsaturated fatty acids by:
The position of the double bond nearest the methyl group
Degree of unsaturation determines what?
Hardness of a fat or oil
The shorter and more unsaturated the more liquid
Palmitic Acid
Number of Carbon Atoms: 16
Number of Double Bonds: 0
State at room temperature: Solid
Fact: Most abundant saturated fatty acid in fats. Animal fats contain large quantities
Stearic Acid
Number of Carbon Atoms: 18
Number of Double Bonds: 0
State at room temperature: Solid
Fact: Animal fats contain large amounts
Oleic Acid
Number of Carbon Atoms: 18
Number of Double Bonds: 1
State at room temperature: Liquid
Fact: Large amounts found in oils from plants and seeds
Linoleic Acid
Number of Carbon Atoms: 18
Number of Double Bonds: 2
State at room temperature: Liquid
Fact: Large amounts found in plant and seed oils. Most abundant polyunsaturated fatty acid in oils
Linolenic Acid
Number of Carbon Atoms: 18
Number of Double Bonds: 3
State at room temperature: Liquid
Arachidonic Acid
Number of Carbon Atoms: 20
Number of Double Bonds: 4
State at room temperature: Liquid
Dietary lipids that contain saturated short and medium chain fatty acids are:
Butterfat and coconut oil
Exceptions to the degree of saturation rule are:
Coconut and palm (tropical) oils but highly saturated (92% and 51% respectively)
Define Triglyceride
Composed of a glycerol molecule, to which 3 fatty acids are attached. Each acid has a carboxylic acid at one end and a methyl at the other.
Define Monoglyceride
One fatty acid attached to a glycerol molecule
Product of food industry
Used as an emulsifier
Margarines, lard and shortening
Can also be found in the human GI tract after a fatty meal (product of fat digestion)
Define Diglyceride
2 fatty acids attached to glycerol
Used as an emulsifier
Food product industry
Define Emulsifier
Food product Industry
Give foods such as ice cream, baked goods, texture to keep fats evenly dispersed.
Define Mixed Triglyceride
3 different fatty acids attached to each glycerol
Most dietary lipids are composed of them
Can vary in length (even-numbered, from 4-30 carbon)
Can vary in degree of saturation
What is the nutritional significance of Triglycerides?
Nutritional significance determined by composition of the fatty acids.
Dominate Dietary Fats
Visible in foods such as: butter, margarine, lard, vegetable oil, salad dressing, fatty meat, chicken skin
Invisible fats include:
Cream, milk, cheese, egg yolks, meat, fish, poultry, nuts, seeds, olives, avocados, bakery items, fried foods, some whole-grains
Define Phospholipid
Lipid that contains phosphorus
Found in almost all cells as a major constituent of cell membranes
Ability to attract water-soluble and fat-soluble substances (Facilitate passage through cell membranes)
Phospholipids in the blood and body fluids also act as emulsifiers (keeping fats in solution)
Explain Lecithin
Phospholipid
Has water-soluble base choline, phosphate molecule and 2 water-insoluble fatty acids attached to glycerol molecule.
Occurs naturally in liver, egg yolks, and soybeans (same as other phospholipids)
As a food additive, lecithin serves as an emulsifier in foods like: cheese, margarine, chocolate bars
Phospholipids make up a vary small amount of dietary lipids. What happens to them when ingested?
Hydrolyze by intestinal enzymes and can be used to produce energy.
Not an essential nutrient as the body can synthesize them as needed
Define Sterol
Lipid with characteristic hydrocarbon ring structure; all sterols are derived from cholesterol, and resemble chicken wire. Hydrophobic (Water-insoluble). Do not contribute energy to the body
Cholesterol
Best known sterol
80% of cholesterol is synthesized in the body (liver and intestine)–Endogenous cholesterol
Also found in animal products not plant products
Cholesterol from dietary sources–Exogenous cholesterol (major sources: egg yolks, meat, poultry, fish, dairy products)
Essential component of cell membranes and is the precursor for the synthesis of bile acids, hormones and vitamin D
High blood cholesterol is a major risk factor for coronary heart disease
Define Oxidation
Occurs when oxygen combines with an unsaturated fatty acid at the double bond. Create unpleasant odour and flavour of rancid fats. Oils that contain high percentage of polyunsaturated fatty acids are more susceptible.
Conditions that accelerate oxidation include: oxygen, light, heat, exposure to metal (iron and copper)
How to avoid oxidation
- Storage
- Add antioxidants (BHA and BHT) serving as oxygen scavengers
- Vitamin E is a biological antioxidant but not often used because of cost
- Partially Hydrogenated the oil to reduce the number of double bonds
Define Hydrogenation
Chemical process by which hydrogen is added to unsaturated oils to reduce the number of double bonds. Used to improve shelf life and attain desired consistency
Consequences of Hydrogenation
- changes polyunsaturated fat to saturated fat
- changes chemical structure of essential fatty acids
- double bonds transform from cis to trans form (risk of heart disease)
What are the essential fatty acids?
Omega-3 and Omega-6
What are the Omega-6 fatty acids?
Linoleic (18-carbon) and Arachidonic (20-carbon)
Arachidonic acid can be synthesized in the body to from its precursor, linoleic acid and is provided by dietary meats. Seed oils are good sources of linoleic acid
What are the fatty acids of the Omega-3 acids?
Linolenic acid (18-carbon) is the “parent” fatty acid. Serves as a precursor to 2 other fatty acids:
Eicosapentaenoic Acid (EPA)
Docosahexaenoic Acid (DHA)
Sources of Linolenic acid: flax, canola, soybean oils, fatty fish, walnuts
Sources of preformed EPA and DHA: fatty fish (sardines, herring, salmon)
Digestion of Fat in the mouth
Some hard fats begin to melt as they reach body temperature. Sublingual salivary gland in base of tongue secrets lingual lipase.
Digestion of Fat in the Stomach
Acid-stable lingual lipase initiates lipid digestion by hydrolyzing one bond of triglycerides to produce diglycerides and fatty acids. Degree of hydrolysis by lingual lipase is minimal for most fats except milk fats. The stomach’s churning mixes fat with water and acid. A gastric lipase accesses and hydrolyze (small amount) fat
Digestion of Fat in the Small Intestine
Cholecystokinin (CCK) signals the gallbladder to release bile (via the common bile duct)
Fat –> Bile –> Emulsified fat
Pancreatic Lipase flows in from the pancreas (pancreatic duct)
Emulsified fat (triglycerides) –> Pancreatic (and intestinal) lipase –> Monoglycerides, glycerol, fatty acids (absorbed)
Digestion of Fat in the Large Intestine
Some fat and cholesterol, trapped in fibre, exit in feces
Define Micelles
Emulsified fat droplets formed by molecules of bile surrounding monoglycerides and fatty acids. Configuration permits solubility in watery digestive fluids and transportation into intestinal cells. Upon arrival lipid contents of micelles diffuse into intestinal cells. Once inside monoglycerides and fatty acids reassemble to new triglycerides
Define Chylomicrons
Newly made triglycerides and other lipids (cholesterol, phospholipids) are packed with protein into lipoprotein transport vehicles known as chylomicrons. Formed in mucosal cell after absorption of dietary lipids. Low in density. Cells all over the body remove the lipids from the chylomicrons as they pass. (Liver and adipose cells are particularity active)
Lipid Absorption
Small digested triglycerides (glycerol and small/medium chain fatty acids) diffuse easily into intestinal cells; and absorbed directly to the bloodstream Larger molecules (monoglycerides and long-chain fatty acids) merge into micelles, diffuse into intestinal cells and then reassemble into new triglycerides. They then form chylomicrons and are released (Pinocytosis) into the lymphatic system. The chylomicrons travel through the lymph to the thoracic duct to enter the blood stream
Lipid transport
Lipoproteins (including chylomicrons) transport fats
Define (Very-low-Density Lipoproteins) VLDL
Lipids made in the liver and those collected from CHYLOMICRON are packaged with proteins as VLDL and travel trough the body. As they travel through the body cells remove triglycerides causing VLDL to shrink. The proportion of lipids shifts and cholesterol becomes the predominant lipid and density increases.
The VLDL becomes and LDL
Define (Low-Density-Lipoproteins) LDL
Low in triglycerides and high in cholesterol. LDL are “bad cholesterol” and circulate the body making their contents available to cells of all tissues–muscles (including the heart), fat stores, mammary glands, etc. The cells take triglycerides, cholesterol and phospholipids to make cell membranes, hormones, other compounds or store for later use. Special LDL receptors on the liver cells play crucial role in control of blood cholesterol and removing LDL from circulation
Define (High-Density-Lipoproteins) HDL
The liver makes HDL “good cholesterol” to remove cholesterol from the cells and carry it back to the liver for recycling and excretion. HDL have anti-inflammatory properties that seem to keep the atherosclerotic plaque from breaking apart causing heart attacks.
The difference between HDL and LDL is the proportions and types of lipids and proteins within them. They are both cholesterol. What are some factors to help lower LDL and raise HDL?
- weight control
- monounsaturated/polyunsaturated instead of saturated fat in the diet
- soluble dietary fibres
- phytochemicals
- moderate alcohol consumption
- physical activity
Roles of fat in the body
- Energy storage and release
2. Insulate and protect body and organs
In the body, triglycerides do what?
- provide energy
- insulate against temperature extremes
- protect against shock
- provide structural material for cell membranes
- participate in cell signalling pathways
Linoleic (Omega-6) and Linolenic (Omega-3) Acids do what in the body?
- Serve as structural parts of cell membranes
- Serve as precursors to the longer fatty acids that can make eicosanoids
Define Eicosanoid
Powerful compounds that participate in blood pressure regulation, blot clot formation, and the immune response to injury and infection
Storing Fat as Fat
Adipose cells store fat after meals when large amounts of chylomicrons and VLDL passes through blood. Enzyme lipoprotein lipase (LPL) hydrolyzes triglycerides from lipoproteins, releasing fatty acids that enter adipose cells. Inside cells, other enzymes reassemble these lipids into triglycerides for storage. Triglycerides fill the adipose cell storing a lot of energy in a relatively small space
Using Fat for Energy
Efficient energy metabolism depends on the energy nutrients – carb, fat, protein – supporting one another. Glucose fragments combine with fat fragments during energy metabolism and fat and carbs help spare protein, providing energy so protein can be used for other important tasks.
Fat supplies 60% of the body’s ongoing energy needs during rest. During prolonged light-moderately intense exercise fat may contribute more
During energy deprivation, what happens?
Serval lipase enzymes (hormone-sensitive lipase) inside the adipose cells respond by dismantling stored triglycerides and releasing the glycerol and fatty acids directly into the blood. Cells then capture these compounds and take them through a series of chemical reactions to yield energy, carbons dioxide, and water
How do Omega-3 helps reduce risk of Heart disease?
- reduce blood triglycerides
- preventing blood clots
- protecting against irregular heart-beats
- lowering blood pressure
- defending against inflammation
- serving as precursors to eicosanoids
Dietary fat, distribution of cholesterol in different types of lipoproteins, total blood cholesterol and dietary cholesterol all affect he risk of cardiovascular disease. TRUE OR FALSE?
TRUE
The type of dietary fat has a greater influence on blood cholesterol levels than does dietary cholesterol. Saturated fats (coconut, palm, animal fats) increase total blood cholesterol and LDL cholesterol. Therefore, the most effective way to decrease blood cholesterol is:
Reducing saturated fats
Polyunsaturated fats-particularly those in Omega-6 fatty acids do what?
Lower blood cholesterol and LDL cholesterol
What is the current dietary advice?
Not to simply cut down on saturated fat, but to replace some saturated fat with sources of polyunsaturated fats
Monounsaturated fatty acids have a… on blood cholesterol levels?
Have a neutral effect on blood cholesterol levels.
Diets rich in MUFA, like the Mediterranean diet are associated with lower risk of cardiovascular disease.
Consuming excessive amounts of polyunsaturated and monounsaturated fats could contribute to obesity
Hydrogenated fats should be reduced as much as possible because they increase the blood cholesterol level and are associated with heart disease. Includes: snack foods, soft/hard margarines, vegetable shortening, baked goods). However, the quantity of these fats in foods has been reduced in the recent years. TRUE OR FALSE?
TRUE
Soluble dietary fibre (pectin and gums) is thought to…
Lower blood cholesterol levels by binding with bile acids, thus hindering reabsorption. Body is then forced to synthesize additional bile acids from cholesterol
Excess energy intake leading to obesity has shown to increase total blood cholesterol and LDL cholesterol. Conversely…
A decrease in body weight has been shown to decrease total blood cholesterol and increase HDL cholesterol
A healthy diet includes:
- low in trans fats
- low in saturated fat
- rich in unsaturated fat (especially Omega-6 fatty acids)
- contains dietary source of DHA and EPA (provided by consuming fatty-fish 2 times/week)
- rich in a variety of dietary fibre
- supplies an energy intake that supports a healthy BMI
DHA (22-carbon) has been found to concentrate in the photoreceptors membranes of the retina and in neural membranes of the brains (important in rapid growth–third trimester). TRUE OR FALSE?
TRUE
Human breasted milk also contains DHA and EPA
Deficiency of essential fatty-acids is rare but can occur when:
- infants fed with low-fat formula or skim milk
- patients suffering from serious burns (loss of body fluids)
- people with bowel resection (severe fat malabsorption)
- long-term, low-fat, total parenteral nutrition (TPN) or gastric feeding tube
Signs of essential fatty acid deficiency include:
- growth retardation
- skin lesions with characteristic dermatitis (eczema), dry, scaly skin
- increased risk of infection
- possible peripheral neuropathy or blurred vision
In the 1970s fat supplied what percentage of energy?
40%
In 1997 what percentage of energy did fat supply?
30%
What percentage of energy comes from saturated fat?
10%
People should reduce their intake of processed meat. TURE OR FALSE?
TRUE
In recent years, consumption of animal fats has decreased as people have switched to leaner meat and low-fat milk. However, the intake of hidden fats, cakes, cookies, French fries, salad dressings, has increased. TRUE OR FALSE?
TRUE
There is no RDA for fat as a general nutrient class but there are suggested maximum and minimum intakes. What are they?
- DRI for total fat is 20-35% of total energy (2000kcal diet ~45-75 grams/day)
- SFA intake be less than 10% total energy
- PUFA is broken down into 2 groups
1. Linoleic Acid (Omega-6): 5-10% total energy (~17 grams/day men and 12 grams/day women)
2. Linolenic Acid (Omega-3): 0.6-1.2% total energy (~1.6 grams/day men and 1.1 grams/day women) - MUFA supply remaining energy from fat (10-15% of total)
- Limit trans fat from process foods (occurs naturally in beef and dairy products)
- No specific recommendation for cholesterol intake
The ratio of Omega-6 to Omega-3 is important because they have different abilities to stimulate or slow down processes in the body.
(Ex. Omega-6 is more inflammatory than Omega-3)
What is the ratio?
Range from 4:1 to 10:1
Omega-3 fatty acids are contained in:
Flaxseed, canola, soybean, walnut oils
Sometimes referred to as ALA (Alpha-linolenic acid)
Omega-6 fatty acids are found in:
Most vegetable oils
A food labelled as containing Omega-3 may not necessarily contain what?
EPA and DHA. Look closely
