Chapter 5 Notes – The Lipids: Fats, Oils, Phospholipids, and Sterols

●Lipids
- A family of organic compounds soluble in organic solvents but not in water
- Include triglycerides (fats and oils), phospholipids, and sterols
●Cholesterol
-A member of the group of lipids known as sterols
- A soft waxy substance made in the body for a variety of purposes
- Also found in animal-derived foods
●Fats
-Lipids that are solid at room temperature
●Cardiovascular Disease (CVD)
- Disease of the heart and blood vessels
- Disease of the arteries of the heart is called coronary heart disease (CHD)

Introducing the Lipids
●Lipids in foods and in the human body fall into three classes
- Triglycerides
about 95% of all lipids in foods and the human body
- Phospholipids
for example, lecithin
- Sterols
for example, cholesterol

The Usefulness of Fats
Fats in the body
●Energy stores
-fats are the body’s chief form of stored energy
●Muscle fuel
-fats provide most of the energy to fuel muscular work
●Emergency reserve
-fats serve as an emergency fuel supply in times of illness and diminished food intake
●Padding
-fats protect the internal organs from shock through fat pads inside the body
●Insulation
-fats insulate against temperature extremes through a fat layer under the skin
●Cell membranes
-fats form the major material of cell membranes
●Raw Materials
-fats are converted to other compounds, such as hormones, bile, vitamin D, as needed
Fats in Food
●Nutrient
-fats provide essential fatty acids
●Energy
-fats provide a concentrated energy source in foods
●Transport
-fats carry fat-soluble vitamins A, D, E, and K along with some phytochemicals, and assist in their absorption
●Raw materials
-fats provide raw material for making needed products
●Sensory appeal
-fats contribute to the taste and smell of foods
●Appetite
-fats stimulate the appetite
●Satiety
-fats contribute to feelings of fullness
●Texture
-fats help make foods tender

Usefulness of Fats in the Body
●Fat
- Body’s chief storage form for the energy from food eaten in excess of need
-valuable survival mechanism for people who live in a feast-or-famine existence
-Provide most of the energy needed to perform much of the body’s work
-especially muscular work
●Most body cells can store only limited fat
- Some cells are specialized for fat storage
-these fat cells seem to expand indefinitely
-the more they store, the larger they grow
-Andipose (fat) tissue secretes hormones and produces enzymes that influence food
intake and affect the body’s use of nutrients
●Glucose, in the form of glycogen, is not the body’s major form of energy storage
-Glycogen stores a large amount of water
-therefore it is heavy and bulky
-thus, the body cannot store enough to provide energy for very long
●Fat is the body’s major storage form of energy
-Fats pack tightly together without water
-Relative to carbohydrate, much more fat can be stored in a small space
-Gram for gram, fats provide more than 2x the energy of carbohydrate
-making fat an efficient storage form of energy
●Body fat
-The amount on a normal-weight person is more than sufficient to provide energy for an entire marathon or to battle disease should the person become ill and stop eating for a while
●Other functions of fat
-Shock absorbers
-pads of fat surround vital internal organs
-Thermoregulation
-fat pads under the skin insulate the body from extremes of temperature
-Cell membranes
-lipids are a component of cell membranes
-Essential nutrients
-the fat-soluble vitamins (A,D,E, and K) are soluble in fat)
-found mainly in foods that contain fat
-absorbed more efficiently from these foods
-fat also aids in the absorption of some phytochemicals
-Essential fatty acids
-serve as raw materials from which the body makes certain required molecules

●The energy density of fats makes food rich in fat valuable in many situations
-For example, a hunter of hiker needs to consume a large amount of food energy to travel long distances or to survive in intensely cold weather
-For a person who is not expending much energy in physical work, the same high-fat foods may deliver many unneeded calories in only a few bites

Usefulness of Fats in Foods
●People naturally like high-fat foods
-As fat becomes less expensive and more available in a given food supply, people seem to choose diets providing greatly increased amounts of fat
-Fats carry many dissolved compounds that give foods enticing aroma and flavors
-Fat also lends tenderness to foods such as meats and baked goods
●Fats contribute to satiety
-the feeling of fullness or satisfaction that people experience after meals
-the fat of swallowed food triggers a series of physiological events that slow the emptying of the stomach and promote satiety
-even before the sensation of fullness stops them people can easily overeat fat-rich foods because of the delicious taste

Triglycerides: Fatty Acids and Glycerol
●Triglyceride = 3 fatty acids + glycerol
-fatty acids
-organic acids composed of carbon chains of various lengths
-each has an acid end and hydrogens attached to all of the carbon atoms of the chain
-differ on the basis of length and degree of saturation
-glycerol
-an organic compound, three carbons long
-serves as the backbone for triglycerides
●Triglycerides usually include a mixture of fatty acids
-the nature of the fatty acids determines if the triglyceride is hard or soft
-mostly shorter-chained fatty acids or unsaturated ones are softer and melt more readily at lower temperatures
●Fats in the diet can affect the types of triglycerides made
-dietary fats are often incorporated into triglycerides in the body
-for example, many animals raised for food can be fed diets containing softer or harder triglycerides to give the animal softer or harder fat
-whichever consumers demand

Saturated versus Unsatured Fatty Acids
●Saturation refers to whether or not a fatty acid chain is holding all of the hydrogen atoms it can hold
-Point of saturation
-site in a molecule where the bonding is such that addition hydrogen atoms can easily be attached
●Saturated fatty acid
-every available bond from the carbons is holding a hydrogen
●Monounsaturated fatty acid
-contains one point of unsaturation
●Polyunsaturated fatty acid (PUFA)
-contains two or more points of unsaturation

●Degree of saturation
-affects the temperature at which fat melts
-in general, the more unsaturated the fatty acids, the more liquid the fat is at room temperature
-in general, the more saturated the fatty acids, the firmer the fat is at room temperature
-Trans fats
-contain unusual fatty acids that are formed during processing
-Animal fats are generally the most saturated
-There is a benefit to heart health when monounsaturated or polyunsaturated fats replace saturated and trans fat in the diet

●Olive Oil
-Rich in monounsaturated fatty acids
-evidence from Mediterranean regions suggests that olive oil confers a degree of protection against heart disease when used in place of other fats
-dark-colored olive oils also deliver valuable phytochemicals

●Canola oil
-rich in both monounsaturated and polyunsaturated fatty acids
-supports heart health when replacing saturated fats in the diet

Phospholipids and Sterols
●Phospholipids = 2 fatty acids + glycerol + a phosphorus-containing molecule
-fatty acid is soluble in fat
-phosphorus is soluble in water
●Phospholipids are emulsifiers
-a substance that mixes with both fat and water and permanently disperses the fat in the water
-forming an emulsion
●Food processors blend fat with watery ingredients by way of emulsification
-the process of mixing lipid with water by adding an emulsifier
-in salad dressings vinegar and oil separate to form two layers; whereas mayonnaise, also made of vinegar and oil, never forms two separate layers
-the difference is the presence of lecithin, an emulsifier, in mayonnaise

●Lecithin and other phospholipids play key roles in the structure of cell membranes
-Phospholipids are able to help fats travel back and forth across the lipid-containing membranes of cells into the watery fluids on both sides
-Lecithin supplements have no special ability to promote health
-the body can make all that it needs

●Sterols
-Large, complicated molecules consisting of interconnected rings of carbon atoms with side chains of carbon, hydrogen, and oxygen
●The sterol cholesterol serves as the precursor for making bile
-an emulsifier made in the liver and stored in the gallbladder
-does not digest fats
-emulsifies fats in such a way that enzymes in the watery fluids may contact it and split the fatty acids from their glycerol for absorption
●Vitamin D and sex hormones are also sterols

●Cholesterols
-component of cell membranes
-can be made by the body
-not an essential nutrient
-forms the major parts of the plaques that narrow arteries in atherosclerosis
-the underlying cause of heart attacks and strokes

Lipids in the Body
●Lipids affect the body’s functioning and condition
Demand special handling because fat separates from water, and body fluids consist largely of water

Digestion and Absorption of Fats
●Tongue
-An enzyme produced by the tongue plays a major role in digesting milk fat in infants
-little importance to digestion in adults
●Stomach
-Fat separates from the watery components and floats as a layer on the top
●Small Intestine
-Bile
-produced by the liver
-stored in the gallbladder
-secreted in the small intestine
-emulsifies fat
●No gallbladder?
-gallbladder is just a storage organ
-liver still produces bile
-delivers it continuously to the small intestine
-those who have had their gallbladder removed must initially reduce their fat intake
-they can no longer store bile and release it at mealtime so they can handle only a little fat at a time
-Emulsified fat particles acted on by fat-digesting enzymes contributed by the pancreas
-fats are split into smaller particles for absorption
-triglycerides – split fatty acids from glycerol
-Free fatty acids, glycerol and monoglycerides cling together in balls surrounded by bile
-in order to be absorbed, fats must pass through the water layer of mucus that coats the absorptive lining of the digestive tract
-bile shuttles the lipids across the mucus layer to the absorptive cells of the intestinal villi
-the cells extract the lipids
-the bile may be absorbed and reused or exit with the feces
-the digestive tract absorbs triglycerides from a meal with up to 98% efficiency
-i.e. little fat is excreted by a healthy system
-the process of fat digestion takes time
-the more fat taken with a meal, the slower the digestive system becomes

●Shorter products of lipid digestion
-Glycerol and short-chain fatty acids pass directly through the cells of the intestinal lining into the bloodstream
-Travel unassisted to the liver
●Larger products of lipid digestion
-without a mechanism to keep it dispersed, large lipid globules would separate out of the watery blood and disrupt the blood’s normal function
-lipoproteins
-clusters of lipids associated with protein
-serve as transport vehicles for lipids in blood and lymph
-major classes include: chylomicrons, VLDLs, LDLs, and HDLs
-monoglycerides and long-chain fatty acids are formed into lipoproteins before being released into the lymph that leads to the blood
-inside intestinal cells, they are reformed into triglycerides and clustered together with proteins and phospholipids
-forming chylomicrons – a type of lipoprotein

How can I use my stored fat for energy?
●Chylomicrons transport triglycerides to the fat depots
-muscles
-breasts
-insulating fat layer under the skin
-etc.
●Fat is stored for later use
-when a person’s body starts to run out of available energy from food, it begins to retrieve stored fat to use for energy
-fat cells dismantle stored fat molecules and release the components into the blood
-upon receiving these components, cells break them down into smaller fragments each of which is combined with a fragment derived from glucose
-the energy-releasing process continues, liberating energy, carbon dioxide, and water
●More of this fat can be used for energy by increasing demand for it
-this can be done by doing either/or
-decreasing intake of food energy
-increasing the body’s expenditure of energy
●Carbohydrate is required for the complete break down of fat into energy
-without carbohydrate the incomplete breakdown of fat produces ketones
-ketones build up in the blood and urine
●Excess carbohydrate can be stored as fat
-this conversion is not efficient
-glucose must be broken down into fragments which are then reassembled into fatty acids
-steps that require energy
-fat requires fewer chemical steps before storage
●Weight-loss dieters
-successful weight loss depends on a low energy intake
-not the proportion of nutrients

Dietary Fat, Cholesterol, and Health
●High intakes of certain dietary fats are associated with serious disease
-diets high in saturated fats or trans fats are at increased risk of heart and artery disease (CVD)
-heart disease is the number-one killer of adults in the U.S. and Canada
-High fat diets are associated with an increased risk of certain types of cancer as well as the health risks associated with obesity

●table 5-2 Recommendations concerning intakes of fats for healthy people (p. 150)

Lipoproteins and Heart Disease Risk
●Major Lipoproteins: VLDL, LDL, HDL
-Very-low-density lipoproteins (BLDL)
-carry triglycerides and other lipids made in the liver to the body cells for their use
-Low-density lipoproteins (LDL)
-transport cholesterol and other lipids to body tissues
-made from VLDL after they have donated many of their triglycerides to body cells
-High-density lipoproteins (HDL)
-carry cholesterol from body cells to the liver for disposal
●The LDL and HDL difference
-LDL
-larger, lighter, and richer in cholesterol than HDL
-Deliver triglycerides and cholesterol from the liver to tissues
-HDL
-smaller, denser, and packaged in more protein than LDL
-scavenge excess cholesterol and phospholipids from tissues for disposal
-Elevated LDL concentrations in the blood are an indication of heart attack risk
-Elevated HDL concentrations in the blood are associated with a low heart attack risk
-The difference is attributable to the proportions of lipids they contain and the tasks they perform
-the difference is not in the type of the cholesterol they carry

●The Importance of LDL and HDL Cholesterol
-Blood LDL and HDL cholesterol account for two major CVD risk factors
-high blood LDL concentration is a predictor of the likelihood of suffering a fatal heart attack or stroke
-the higher the LDL, the earlier the episode is expected to occur
-high HDL cholesterol lowers disease risk
●Risk factors that cannot be changed
-increasing age
-being male
-family history of premature heart disease

●Risk factors that a person can often control
-High blood LDL; low blood HDL
-High blood pressure
-Diabetes
-Obesity
-Physical inactivity
-Cigarette smoking
-Atherogenic diet

What does Food Cholesterol Have to Do with Blood Cholesterol?
●Most saturated food fats and trans fats raise blood cholesterol more than food cholesterol does
-high blood cholesterol is an indicator of risk for CVD
-main dietary factors associated with elevated blood cholesterol are high saturated fat and trans fat intakes
●Heart disease-LDL link
-When high blood cholesterol signifies a risk of heart disease, it is because the LDL are carrying cholesterol, made mostly from saturated fat in the diet, to body tissue
-When high blood cholesterol is in HDL, cholesterol is being carried away from body tissues

●Genetics
-about 60% of people exhibit little increase in their blood cholesterol even with a high dietary intake
-some people respond to high dietary cholesterol intake with greatly increased blood cholesterol
-a few individuals have inherited a total inability to clear from their blood the cholesterol they have eaten and absorbed
-those with a genetic tendency toward high blood cholesterol must strictly limit fats and refrain from eating foods rich in cholesterol
-for most others, a limited amount of liver, eggs, and other cholesterol-containing food poses no threat for incurring high blood cholesterol
-the body slows cholesterol synthesis when the diet provides greater amounts
-Moderation, not elimination, is the key for most people as far as cholesterol-containing foods are concerned

Lowering LDL Cholesterol
●To lower high blood pressure
-reduce fat intake
-especially saturated and trans fats
-success is affected by genetics
-food trimmed of fat is also trimmed of much of its saturated fat and energy
●HDL Cholesterol
-Dietary measures are generally ineffective at significantly raising its concentration
-regular physical activity defends against heart disease partly because it effectively raises HDL

●LDL is susceptible to damage by oxidation
-the interaction of a compound with oxygen
-in this case, a damaging effect by a chemically reactive form of oxygen
-evidence indicates that oxidation of the lipid part of LDL is injurious to the arteries of the heart

●Dietary antioxidants may slow LDL oxidation
-vitamins C and E, selenium, antioxidant phytochemicals

Recommendations Applied
●Health authorities
-some recommend that all adults take steps to reduce their LDL cholesterol
-some recommend that only those medically identified as having an elevated risk for heart disease need to take steps to lower their LDL cholesterol
●A good idea to choose a diet that
-provides 20%-35% of its calories from fat
-keeps saturated fat intake below 10% of caloric intake
-keeps trans fat intake below 1% of caloric intake
-substitute monounsaturated or polyunsaturated fat for saturated and trans fat
-note: instead of, NOT in addition too
-Fruits, vegetables, and whole grains
-supply abundant nutrients and antioxidants along with beneficial fiber
-Cholesterol intake
-proceed with caution
-eggs, shellfish, liver, and other cholesterol-containing foods are nutritious
-cholesterol cannot be omitted from the diet without omitting nutritious foods
-many high-cholesterol foods are also high in saturated fat
Think Fitness: Why Exercise the Body for the Health of the Heart?
●Response of blood, arteries, heart, and other body tissues to exercise
-blood HDL concentration increases
-shifting blood lipids in a healthy direction
-circulation improves
-easing delivery of blood to the heart
-a larger volume of blood is pumped with each heartbeat
-reducing the heart’s workload
-the body grows leaner
-reducing overall risk of cardiovascular disease

Essential Polunsaturated Fatty Acids
●Linoleic acid and linolenic acid
-the only fatty acids that cannot be synthesized by the body
-essential nutrients
-polyunsaturated fatty acids
-used by the body to make eicosanoids
-biologically active compounds that regulate body functions
●Eicosanoids regulate functions such as
-muscle relaxation and contraction
-blood vessel dilation and constriction
-blood clot formation
-blood lipids
-response to injury and infection
-fever
-inflammation
-pain
●DRI:
-Linoleic acid
-5%-10% of total calorie intake
-young men: 17g/day
-young women: 12 g/day
-Linoleic acid
-0.6%-1.2% of total calorie intake
-men: 1.6 g/day
-women: 1.1 g/day

Deficiencies of Essential Fatty Acids
●Deficiency of all polyunsaturated fatty acids leads to the appearance of:
-symptoms of reproductive failure
-skin abnormalities
-kidney disorders
-liver disorders

Omega-6 and Omega-3 Fatty Acid Families
●Linoleic acid
-an omega-6 fatty acid
-a polyunsaturated fatty acid with its endmost double bond 6 carbons from the end of the chain
-can be used to produce other omega-6 fatty acids
-Arachidonic acid
-starting material from which a number of eicosanoids are made
●Linolenic acid
-an omega-3 fatty acid
-a polyunsaturated fatty acid with its endmost double bond carbons from the end of the chain
-can be used to produce other omega-3 fatty acids
-EPA and DHA
-body makes limited amounts
-abundant in fish oils
●EPA and DHA
-a diet that includes two meals of fatty fish each week can reduce deaths and illness from heart disease
-especially in people who have already suffered a heart attack
-Fish is more beneficial than fish oil supplements

●Omega-3 fatty acids
-support immunity
-inhibit the development of certain cancers

Recommendations for Omega-3 Fatty Acid Intake
●For healthy children and adults
-a normal balanced diet that includes grains, seeds, nut, leafy vegetables, oils, and fish supplies all the needed forms of fatty acids in abundance and prevents deficiencies
-including fatty fish in a meal 2-3 times a week, for a total of about 12-14 ounces of fish/week, can help achieve a healthy balance between omega-3 and omega-6 fatty acid intakes needed for health

●Foods high in omega-6 fatty acids should be consumed in moderation
-most vegetable oils and other fats
●Food preparation
-fish should be grilled, baked, or broiled
-conserves EPA and DHA versus fried or frozen fish
-frying adds saturated and trans fats
Food sources of Omega-6 and Omega-3 Fatty acids
●Omega-6
Linoleic acid – leafy vegetables, seeds, nuts, grains, vegetable oils (corn, cottonseed, safflower, sesame, soybean, sunflower), poultry fat

●Omega-3
Linolenic acid – oils (canola, flaxseed, soybean, walnut, wheat germ, liquid or soft margarine made from canola or soybean oil) nuts and seeds (butternuts, flaxseeds, walnuts, soybeans) vegetables (soybeans

●EPA and DHA – Human milk, fatty coldwater fish (mackerel, salmon, bluefish, mullet, sablefish, menhaden, anchovy, herring, lake trout, sardines, tuna)

Fish oil supplements
●Taking fish oil supplements is not recommended
-may raise LDL cholesterol
-high omega-3 polyunsaturated fatty acid intake may
-increase bleeding time
-interfere with wound healing
-suppress immune function
-lack other beneficial nutrients found in fish
-iodine
-selenium
-often made from fish skins and liver
-may have accumulated toxic concentrations of
-pesticides
-heavy metals, such as mercury
-other industrial contaminants
-Fish oil naturally contains high levels of two of the most potentially toxic vitamins
-A and D
-Are expensive
-Excessive amounts of either omega-3 or omega-6 fatty acids
-can interfere with normal functions that depend on a proper balance between the two

The Effects of Processing on Unsaturated Fats
●Vegetable oils make up most of the added fat in the U.S. diet
-fast-food chains use them for frying
-food manufacturers add them to processed foods
-consumers tend to choose margarine over butter
●Vegetable oils tend to be less saturated than animal fats

What is “Hydrogenated Vegetable Oil”, and What’s it doing in my chocolate chip cookies?
●Hydrogenation
-the process of adding hydrogen to unsaturaged fatty acids to make the fat more solid and resistant to the chemical change of oxidation
●Points of saturation
-vulnerable to attack by oxygen
-when oxidized the oils become rancid
-cooking oils should be stored in tightly covered containers that exclude air
-if stored for long periods, they need refrigeration to retard oxidation
-prevents spoilage of unsaturated fats
-makes unsaturated fats harder and more stable when heated to high temperatures
-hydrogenated oil is suitable for purpose such as frying; it has a high smoking point
-the temperature at which fat gives off an acrid blue gas
●Hydrogenated oils
-easy to handle
-easy to spread
-store well
●Once fully hydrogenated, an oil loses both its unsaturated character and health benefits
-hydrogenation also affects some vitamins
-for example, vitamin K activity is decreased

●An alternative to hydrogenation
-Addition of a chemical preservative that will compete for oxygen
-thus, protecting the oil
-the additives are antioxidants
-work like vitamin E
-react with oxygen before it can do damage
-For example, BHA and BHT
-Keep refrigerated

What are Trans Fatty Acids and Are they Harmful?
●Trans fats
-unusual saturated fatty acids
-similar in shape to saturated fatty acid
-not made by the body
-naturally occur in tiny amounts mainly in dairy foods and beef
-affect the body’s health

●Consumption of trans fats
-raise LDL and lower HDL cholesterol
-produce inflammation
-thus, increasing the risk of heart disease
-DRI: as little as possible

●Diets high in total fats and especially in trans fats
-may be associated with cancer risk
-to date, there is no evidence that trans fats themselves play a specific role in promoting or causing cancer

Fat in the Diet
●Fat delivers more calorie per bite than the other energy-yeilding nutrients
●Limiting energy intake may be important to maintaining good health
●Fat is necessary for health
-People who try to eliminate fat from their diet put their health at rise
-most adults need about 20% of their daily energy from fat
●Average U.S. diet
-1965: 45% of calories from fat
-Now: 35% of calories from fat
-Problem: despite the percentage of total calorie reduction the actual amount of fat consumed has increased
-the number of grams of carbohydrate has increased even more
-net result: an increase in the number of calories consumed
●Lessons to be learned
-recognize the fats in food
-keep consumption of harmful saturated and trans fats to a minimum
-distinguish these fats from the more beneficial unsaturated fats
-control portion sizes
-particularly of fatty foods

●USDA Food Guide
-Oils always contain fat
-Solid fats group always contains fat
-meat, poultry, fish, legumes, eggs, and nuts group always contains fat
-milk, yogurt and cheese group sometimes contains fat
-grains group sometimes contains fat
-most unprocessed vegetables and fruits are fat-free; except
-avacados and olives
-rich in monounsaturated fats
-unprocessed grains contain little or no fat

●Visible fat
-example: fat trimmed from a steak
●Invisible Fat
-Examples:
-marbling of meat
-fat ground into lunch meats and hamburger
-fats blended into sauces of mixed dishes
-fats in avocado, biscuits, cheese, coconuts, other nuts, olives, and fried foods
-On the rise in U.S. diets

●Olestra
-An artificial fat: Olestra
-A sucrose polymer
-chemically, bears some resemblance to an ordinary fat
●Human enzymes of the digestive tract do not recognize the molecules of loestra
-cannot split its fatty acids from its sucrose
-passes through the digestive tract and exits intact
●Properties are identical to those of fats and oils when used in frying, cooking, and baking
●Aside for a slight aftertaste, to many people it tastes like fat
●Safe in Most regards
●When consumed in large quantities can cause
-Digestive distress
-Nutrient losses
-Losses of phytochemicals
●May be capable of causing
-Diarrhea
-gas
-cramping
-an urgent need to defecate

●Oily olestra can creep through the feces and leak uncontrollably from the anus
-producing smelly, dark yellow stains on underwear
●A potent solvent for the fat-soluble vitamins and other fat-soluble substances in food
-absorption of these substances are reduced when a meal contains olestra
-olestra dissolves them and carries them out of the digestive tract
-to compensate, olestra is fortified with vitamins A, D, E, and K
●Causes the loss of health-promoting phytochemicals
-3 grams/day of olestra reduced absorption of lycopene by about 40%

●Pros of Olestra
-zero calories
-zero fat, saturated fat, and trans fat
-zero cholesterol
-withstands frying
-withstands baking
-tastes like fat
●Cons of Olestra
-vitamin losses
-phytochemical losses
-possible digestive upset
-possible anal leakage
-slight aftertaste
-expensive
-no long-term studies in children

Meat, Poultry, Fish, Legumes, Eggs, and Nuts
●Meats conceal a large amount of the fat people consume
-much of it is saturated fat
-organize meats into four categories based on their fat content (as the exchange lists do)
-very lean
-lean
-medium-fat
-high-fat
●USDA Food Guide
-suggests most adults limit intake to 5-6 oz. per day
-a very small amount by average consumption standards
-a small fast-food hamburger weighs about 3 oz
-a steak served in a restaurant often runs 8, 12, or 16 oz
-more than a whole day’s meat allowance
Milk, Yogurt and Cheese
●Some milk products contain fat
-Homogenizing whole milk
-milk processors blend in the cream
-which otherwise would float to the top and could be removed by skimming
●1 cup of whole milk
-versus fat-free milk
-contains the same amount of protein and carbohydrate as fat-free milk
-contains about 60 extra calories from fat
-versus reduced-fat (2 percent fat) milk
-45 calories from fat
-whole milk contains only 1-2 teaspoons of fat by volume
-which nearly doubles the calories in the milk
●Cheeses are the single greatest contributor of saturated fat in the diet
●Among plant food fats
-only the lipids of palm oil and coconut oil rank higher for saturation than the butterfat in fatty dairy products
Grains
●In their natural state, grains are very low in fat
-fat, including saturated fat and trans fat, may be added during manufacturing, processing, or cooking
-the fats in these foods can be difficult to detect

High-Fat Foods
●DRI recommendations for Fat
-To promote low rates of heart disease, diabetes, obesity, and cancer a diet should:
-get no more than 35% of its calories from fat
-be low in saturated and trans fats
-replace these fats with unsaturated fats
-control energy intake

●Olive Oil: The Potential connection
-The traditional Mediterranean diets are exemplary in their use of “good” fats
-especially olives and their oils
-when used in place of butter, meat fats, etc. olive oil may protect against heart disease
●How olive oil may protect against heart disease
-Lowering total and LDL cholesterol and not lowering HDL cholesterol or raising triglycerides
-Lowering LDL cholesterol’s vulnerability to oxidation
-Lowering blood-clotting factors
-Providing phytochemicals that act as antioxidants
-Lowering blood pressure

●The Mediterranean Diet: Beyond Olive Oil
-Olive oil does not reserve all the credit for the low rates of heart disease among those consuming a traditional Mediterranean diet
-Each of the countries bordering the Mediterranean Sea has its own culture, tradition, and dietary habits
-however, there are some common characteristics
●Common characteristics of traditional Mediterranean diets
-Crusty breads
-Whole grains
-Nuts
-Potatoes
-Pastas
-A variety of vegetables
-including wild greens
-A variety of legumes
-Feta and mozzarella cheese and yogurt
-Fruits
-especially grapes and figs
-some fish and other seafood
-poultry
-a few eggs
-a little meat
-along with olives and olive oil, principal sources of fat are nuts and fish
-rarely use butter
-rarely encounter saturated fats

●Traditional Mediterranean Diets are:
-low in saturated fat
-very low in trans fat
-rich in unsaturated fat
-rich in complex carbohydrates and fiber
-rich in nutrients and phytochemicals that support good health

●Major sources of saturated fat in the U.S. diet
-fatty meats
-over a third of the fat in most meats is saturated
-whole-milk products
-over half the fat in whole milk, and other high-fat diary products, is saturated
-coconut and palm oils
-mostly used in commercially prepared foods

 

Chapter 5 – The Lipids: Fats, Oils, Phospholipids, and Sterols

Introducing the Lipids
Lipid – a family of organic compounds soluble in organic solvents but not in water
95% are triglycerides – made up of three units of fatty acids and one unit of glycerol
other classes are phospholipids (lecithin) and sterols (cholesterol).
Phospholipids are similar to triglycerides but with a phosphorus-containing acid instead of one of the fatty acids

The Usefulness of Fats
In the body:
Energy stores – fats are the body’s chief form of stored energy
Muscle fuel – fats provide most of the energy to fuel muscular work
Padding – fats protect the internal organs from shock through fat pads inside the body cavity
Insulation – fats insulate against temperature extremes through a fat layer under the skin
Cell membranes – fats form the major material of cell membranes
Raw materials – fats are converted to other compounds, such as hormones, bile, and vitamin D

In foods:
Nutrient – fats provide essential fatty acids
Energy – fats provide a concentrated energy source in foods
Transport – fats carry fat-soluble vitamins A, D, E, and K along with some phytochemicals, and assist in their absorption
Raw materials – fats provide raw material for making needed products
Sensory appeal – fats contribute to the taste and smell of foods
Appetite – fats stimulate the appetite
Satiety – fats contribute to feelings of fullness
Texture – fats help make food tender

-most body cells can store only limited amounts of fat but some cells are specialized for fat storage.  These fat cells seem able to expand almost indefinitely – the more fat they store, the larger they grow.
-andipose (fat) tissue secretes hormones that help regulate the appetite and influence other body functions
-fats pack tightly together without water and can store twice as much energy as carbohydrate glucose in a small space

A Close Look At Lipids
Triglycerides: Fatty Acids and Glycerol
Fatty acids-organic acids composed of carbon chains of various lengths.
-most fatty acids are found in triglycerides
-fatty acids can differ in chain length or in degree of saturation
depending on which fatty acids are in a triglyceride, a fat will be hard or soft
-shorter chain fatty acids, more unsaturated, are softer and melt more at room temperature

Saturated versus Unsaturated Fats
-saturation refers to whether or not a fatty acid chain is holding all of the hydrogen atoms possible (having no points of unsaturation)
one point of unsaturation = monounsaturated fatty acid
two or more points = polyunsaturated fatty acid
-the more unsaturated the fatty acid, the more liquid it is at room temperature
Phospholipids
-consists of a molecule of glycerol with two, rather than three, fatty acids attached.  In place of the third is a molecule containing phosphorus
-is soluble in water
-can serve as an emulsifier – a substance that mixes with both fat and water and
permanently disperses the fat in the water
-lecithin and other phospholipids play key roles in the structure of cell membranes by acting as emulsifiers and helping fats travel back and forth across the lipid-containing membranes of cells into the watery fluids on both sides
-has health-promoting properties, ability to lower blood cholesterol
Sterols
-large complicated molecules consisting of interconnected rings of carbon atoms with side chains of carbon, hydrogen, and oxygen
-cholesterol serves as the raw material for making bile (emulsifier) which is important to digestion
-other sterols include vitamin D, which is made from cholesterol and steroid hormones
--cholesterol forms major part of plaques that narrow the arteries in artherosclerosis, underlying cause of heart attacks and strokes

Lipids in the Body

Digestion and Absorption of Fats:
-enzyme produced by the tongue plays major role in digesting milk fat in infants
-in stomach fat separates from the watery components and floats as a layer on the top
-little fat digestion takes place in the stomach
-one end of bile molecules attract and hold fat while other is attracted to and holds water. 
-by the time fat enters small intestine, gallbladder (stores liver’s output of bile) has contracted and squirted bile into intestine.  Bile mixes fat particles with watery fluid by emulsifying them, suspending them in fluid until fat-digesting enzymes contributing by the pancreas can split them into smaller particles for absorption
-when intestinal contents are emulsified, fat-splitting enzymes act on triglycerides to split fatty acids from their glycerol backgrounds.
-fats then must travel through mucus coating of digestive tract lining to absorptive cells of intestinal villi.  Cells extract the lipids.
-very little fat is excreted by healthy system
-person without a gallbladder will still produce bile from the liver but delivers it continuously to the small intestine.  Initially they must reduce their fat intakes because they can no longer store bile and release it at mealtimes.  Their systems can handle only a small amount of fat at a time

Transport of Fats:
-smaller parts of lipid digestion pass directly into the bloodstream to the liver
-glycerol and shorter-chain fatty acids
-larger lipids must form lipoproteins before they can be released into the lymph
lipoproteins – clusters of lipids associated with protein, which serve as transport vehicles for lipids in blood and lymph.  Major classes are the chylomicrons, the VLDL, the LDL, and the HDL
-inside the intestinal cells they are re-formed into triglycerides and clustered together with proteins and phospholipids to form chylomicrons
chylomicrons – clusters formed when lipids from a meal are combined with carrier proteins in the cells of the intestinal lining.  Transport food fats through the watery body fluids to the liver and other tissues
Key point – small lipids travel in the bloodstream unassisted.  Large Lipids are incorporated into chylomicrons for transport in the lymph and blood.  Blood and other body fluids are watery, so fats need special transport vehicles – the lipoproteins – to carry them in these fluids.

How can I use my stored fat for energy?
-when a body starts to run out of available fuel from food it begins to use stored fat to use for energy.  Fat cells respond by dismantling stored fat molecules and releasing fat components into the blood.  Energy-hungry cells break these components down into smaller fragments.  Each fragment is combined with a fragment derived from glucose and the energy-releasing process continues, liberating energy, carbon dioxide, and water. 
-carbohydrate must be available when fat is broken down.  Without it, ketones will build up in the blood and urine

Dietary Fat, Cholesterol, and Health
High intakes of certain dietary fats are associated with serious diseases
-heart and artery disease is number-one killer of adults in US
-suggested that high-fat diet may incur greater-than-average risk of some cancers
-obesity
Major Lipoproteins:
Very-low-density lipoproteins (VLDL) – carry triglycerides and other lipids made in the liver to the body cells for their use
Low-density lipoproteins (LDL) – transport cholesterol and other lipids to the tissues.  LDL are made from VLDL after they have donated may of their triglycerides to body cells
High-density lipoproteins (HDL) – lipoproteins that return cholesterol from the tissues to the liver for dismantling and disposal; contain a large proportion of protein. Critical in the process of carrying cholesterol away from body cells to the liver for disposal

HDL and LDL play major roles with regard to heart health and are the focus of most recommendations made for reducing the risk of heart disease
-elevated LDL concentrations in the blood are a sign of high risk of heart attack
-elevated HDL concentrations are associated with a low risk
difference in health lies in the proportions of lipids they contain and tasks they perform

What does food cholesterol have to do with blood cholesterol?
Most saturated fats raise blood cholesterol more than food cholesterol does
-main dietary factors associated with elevated blood cholesterol are high saturated fat and trans fat intakes
-dietary cholesterol makes smaller but still significant contribution to elevated blood cholesterol

Lowering LDL Cholesterol
-trim the fat, especially saturated and trans fat, from foods
-eliminate as much saturated and trans fats as possible

Essential Polyunsaturated Fatty Acids
Body can use carbohydrate, fat, or protein to synthesize nearly all fatty acids.
-exceptions are linoleic acid and linolenic acid.  These must be supplied by diet
-serve as raw materials from which the body makes eicosanoids – biologically active compounds that regulate body functions, affecting a wide range of diverse body functions: muscle relaxation and contraction, blood vessel dilation and blood vessel constriction, blood clot formation, blood lipid regulation, and immune response to injury and infection including fever, inflammation and pain.
-aspirin relieves fever, inflammation and pain by slowing synthesis of eicosanoids

Deficiencies of Essential Fatty Acids:
-When diet is deficient in all of the polyunsaturated fatty acids symptoms of reproductive failure, skin abnormalities, and kidney and liver disorders appear
-in infants, growth is retarded and vision is impaired
-body stores some essential fatty acids so extreme deficiency disorders are seldom seen except when intentionally induced in research or on rare occasions when inadequate diets have been provided to infants or hospital patients by mistake

hydrogenation – process of adding hydrogen to unsaturated fatty acids to make fat more solid and resistant to the chemical change of oxidation
-when unsaturated points in oils of food are oxidized the oils become rancid and food tastes “off”
-making fats harder and more stable when heated at high temperatures prevents spoilage
-resulting product is more saturated as they accept hydrogen and the oil hardens
-more spread able, more resistant to damage from oxidation or breakdown from high
temperatures.
Hydrogenated oil has a high smoking point so it is suitable for frying – temperature at which fat gives off an acrid blue gas

Key point – vegetable oils become more saturated when they are hydrogenated.  Hydrogenated fats resist rancidity better, are firmer textured, and have a higher smoking point than saturated oils, but they also lose the health benefits of unsaturated oils

Trans fatty acids – not made by the body by occur naturally in tiny amounts mainly in dairy foods and beef, fatty acids with unusual shapes that can arise when polyunsaturated oils are hydrogenated
-consuming fatty acids raise LDL and lower HDL by producing inflammation
DRI committee concludes people should consume as little trans fat as possible

Key point – The process of hydrogenation also creates trans fatty acids.  Trans fats act somewhat like saturated fats in the body