Chapter 6 Lipids Flashcards
Triglyceride
甘油三酸酯
Three types of lipids
Triglycerides, phospholipids, and sterols
What can lipid solute in?
Lipids cannot solute in water, but can dissolve in organic solvent, like chloroform, benzene, and ether.
The most common type of lipid
Triglyceride, most common in food and body. 95% of the fat we eat and stored in body is triglyceride.
Structure of triglyceride
Three fatty acids attached a glycerol as backbone.
Esterification
The process of attaching fatty acids to glycerol is called esterification. One water molecule will be released when each fatty acid bonds to glycerol.
Hydrolysis
The release of fatty acids from glycerol.
Basic structure of free fatty acids
Long chains of carbon atoms linked together and surrounded by hydrogen atoms.
Carbon Chains vary in three ways
The number of carbon in one chain, the extent to which the chain is saturated with hydrogen, and the shape of chain (straight or bent).
Long-chain fatty acid
Have 12 or more carbon atoms. Fatty acid in beef, lamb, pork, and most plant oil is long-chain fatty acid. It need longest time to digest and transport via lymphatic system.
Medium-chain fatty acid
Have 6 to 10 carbon atoms. It digest as quickly as glucose, and it transport via portal system. Coconut and palm kernel oil is example of it.
Short-chain fatty acid
Less than 6 carbon atoms. They are rapidly digested and transported via portal system. 3% of the fat in butter is short-chain fatty acid.
How many bonds can carbon, oxygen, and hydrogen form?
Carbon: 4
Oxgen: 2
Hydrogen: 1
Number of double bonds or polyunsaturated fatty acid
at least 2
The shape of (un)saturated fatty acid
The shape of saturated or trans fatty acid is straight, and the shape of unsaturated fatty acid is bent or kinked.
The shape of trans fatty acid
The double bonds of it zigzag back and forth across the carbon chain. It has hydrogen next to the double bonds on opposite sides of the carbon chain, is straight and resembles a saturated fatty acid.
Hydrogenation
Hydrogenation adds hydrogen to carbon chain of unsaturated fat. As the amount of added hydrogen increases, the unsaturated acid becomes more and more saturated and increasingly solid.
PUFAs
Polyunsaturated fatty acids
Essential fatty acids
Linoleic acids(omega-6) and Alpha linoleic acids(omega-3)
Why we can only get EFAs from food?
Because human’s body cannot synthesize essential fatty acids with double bond before the 9th carbon in the chain, counting from the omega end.
What identify the fatty acid’s family?
The location of the first double bond closest to the omega carbon (methyl ends) identified the fatty acid’s family. If the first double bond occurs after the 6th carbon on the chain, it is called an omega-6 fatty acid.
EPA and DHA are made from
Alpha linoleic acid
Eicosanoids
Are hormone like compounds that affect the region of body where it is produced. They are called of local hormones, because they are produced and used at the same place.
Hidden fat
In some foods, hidden fat is invisible like whole milk, cheese, cookies, cakes. We need to read the nutrient label to get more information.
Replacement of fat
In order to reduce the fat intake of consumers and still enjoy the mouthfeel, food companies use water, protein, or forms of carb such as fiber, starch derivatives, and gums to replace the fat. Those things are made of fat and sucrose, but contain few or no calories, because they are hard to digest and absorbed.
trans fatty acids
反式脂肪酸
Source of saturated fatty acid
Coconut oil, butter, palm oil, lard or beef fat.
Source of monounsaturated fatty acid
Olive oil, Canola oil, peanut oil.
Source of polyunsaturated fatty acid
Safflower acid, Sunflower acid, Corn oil, Soybean oil.
Source of trans fatty acid
Tub margarine, stick margarine, shortening
Functions of triglycerides
Provide energy, provide compact energy storage, insulate and cushion vital organs, help transport nutrients to bloodstream.
How much energy can triglycerides provide per gram
9 cal/g
The main fuel source for body cells
Triglycerides are the main fuel source for all body cells, except nervous system and red blood cells. When you are doing light physical exercise, triglycerides provide 30% t0 70% energy you burn.
Triglycerides provide energy storage
Excess calories from carb, fat, protein, and alcohol can be converted to fatty acids and then triglycerides. Triglycerides are stable and calorie dense. Also triglycerides and expand to an average 2 to 3 times their normal size.
The portion of water and lipid in fat cells
80% lipid and 20% water and protein.
Although it is important to have some fat store in our bodies
very small fat or very large fat can pose numerous health risks.
Where is made mostly of triglycerides?
The insulating layer of fat just beneath the skin. Called subcutaneous fat.皮下脂肪
Subcutaneous
皮下的
The function of insulating the body
Keep the temperature. Cushion the organs and protect them from jostling around and getting injured.
Aid fat soluble vitamins absorption and transport
Fat found in food carry fat-soluble vitamins (A,D,E.K) to small intestine. The fat soluble vitamin are transported in the bloodstream in the same manner as dietary fat.
Function of omega-3 fatty acids
Is needed during fetal life and infancy for normal development and function of the retina. Starting of the first few weeks of embryonic life is vital for development and maturation of nervous system
Eicosanoids
They are made of essential fatty acids, have over 100 different actions, such as regulate blood pressure, blood clotting,
Functions of essential fatty acids
Along with phospholipid and cholesterol are structural components of cell membrane. They keep cell membrane fluid and flexible, so that substances can flow into and out the membrane.
Phospholipid
Are found large amount in food and body, especially in brain.
Structure of phospholipid
It is similar to triglycerides, but one exception. One fatty acid is replaced by a compound(phosphate) that contains phosphorus and usually attached with nitrogen.
And important quality of phospholipid
Phosphate gives phospholipid an important quality that let these fat function in a watery environment which avoid clumping together.
Two major roles of phospholipid
As cell membrane and emulsifier.
Main emulsifier in body
Bile and lecithins.
Emulsifier
Emulsifier is a compound form a shell around the fat droplets and make them suspended in water but not clump together. It is essential for fat to be digested and transported through the bloodstream.
The face of hydrophilic tail
Outside of the shell is made of hydrophilic that heads extend away from fat droplet.
Phospholipid in food
Are used as an emulsifier in food preparation and manufacturing which function as in body.
Source of phospholipid
Phospholipid can be produced by body and gutted from food. Although lecithins supplements are available, they are not needed because liver can produces sufficient of lecithin itself.
High doses of lecithin will cause
Diarrhea, gas, and weight gain.
Structure of sterol
The carbons are mostly arranged in multi-ringed structure.
The most well known sterol
Cholesterol
Functions of cholesterol
Are required to synthesize many compounds, such as sex hormones. Also required to make bile. Along with phospholipid to form the cell membranes and allows the fat-soluble substances flow in and out the cells. Also forms the shell of chylomicrons(droplets that transport lipid). The shell allows fat droplets float in water-based bloodstream.
Amount of cholesterol per day
American diets supply 180 to 325mg per day. We absorb 40% to 60%.
Source of cholesterol
Animal origin(such as meat, poultry, eggs) and diary products.
Low intake of fat may cause
Increases the chance of getting too little vitamin E and essential fatty acids and may adversely affect blood level of triglycerides.
When will monounsaturated fats supply the extra calories?
When the calorie from cholesterol exceeds 30%.
How much cholesterol should we intake
No more than 300mg.
Low fat diets can help
lower the risk of heart disease and even reverse the damage that already done to the arteries. However, low fat diets may raise the carb intake, which will elevate the triglycerides in blood and cause heart disease.
Mediterranean diet
Olive oil as main fat Abundant fruit, veggies, grains, seeds, beans, and nuts daily. Minimally processed, fresh, seasonally, locally grown foods. Small amount of cheese and yogurt daily. Low moderate amount of fish weekly Limited eggs and red meats Regular exercise Moderate drink of wine at mealtime.
Recommended intake of essential fatty acid
less than 120 cal/day for women, and 170 cal/day for men
Insufficient of essential fatty acid will cause
Diarrhea, slowed growth, delayed healing of wound and infections, flaky and itchy skin.
How to meet omega-3 fat needs
Eat at least 2 portions of cold water fish weekly
Long chain omega 3 fatty acids are
EPA(eicosapentaenoic acid) and DHA(docosahexaenoic acid)
The amount of total fat we should take daily
20% to 35% of calories for most age groups.
The digestion of triglycerides
- The lingual lipase is secreted in the mouth. It can break down triglycerides with short chain and medium chain which can be found in milk fat.
- In stomach, gastric lipase is secreted, it break down the triglycerides into monoglycerides and diglycerides, and free fatty acids. They are floating on top of the watery content in stomach, which limits the extent of lipid digestion.
- Fat digestion most occurs in small intestine. Fat triggers the release of hormone CCK which stimulates the release of bile from gallbladder, lipase, colipase from pancreas. Bile break the fats into droplets called micelles and form a shell around it to ensure it suspend in the water-based intestinal content.
Emulsification
It increases the surface of lipids and allows pancreatic lipase efficiently break down the triglycerides into monoglycerides and free fatty acids.
Why the digestion of fat is very quick?
Because the release of pancreatic lipase it much greater than the amount we need.
The function of colipase
Help the lipase latch onto the micelles
Digestion of phospholipids
They are also digest most in small intestine. Enzyme from pancreas and small intestine break phospholipid into their basic parts: glycerol, fatty acids, phosphoric acids and other components.
Digestion of cholesterol
Cholesterol esters(cholesterol with a fatty acid attached) are broken down to cholesterol and free fatty acids by a pancreatic enzyme called cholesterol esterase.
How much dietary fat will be absorbed?
95%
Which kind of fatty acids absorbed by cardiovascular?
short chain and medium chain fatty acids. They transported via portal vein which leads directly to liver.
Absorption of long chain fatty acids
Long chain fatty acids are re-esterfied into triglycerides in absorptive cells. After further packaging, they enter the lymphatic circulation along with fat-solube vitamins and dietary cholesterols.
Lipoprotein
Lipid is transported in the blood as lipoproteins called chylomicrons, very-low density, intermediate-density, low-density, and high density lipoproteins.
Structure of lipoproteins
Lipoproteins has a core made of lipid, and covered with a shell made of protein, phospholipid, and cholesterol. The shell let the lipoprotein circulate in the blood.
High polyunsaturated fat intake
More than 10% of calorie intake will increase the amount of cholesterol in arteries and raise the risk of cardiovascular disease. Also will impair the ability of immune system to fight disease.
Diets include the omega 3 are good to
Will reduce the blood clotting ability and affect heart rhythm for somebody, this will reduce the risk of heart attack.
Excessive omega 3 intake
Will reduce the ability of immune system and allow the uncontrolled bleeding. Even cause hemorrhagic stroke.
