chapter 5 - lipids

lipids

soluble in organic solvents but not in water (and our body is mostly water)

triglycerides

one of the three main classes of dietary lipids

• made up of 3 fatty acids and 1 glycerol (which is made from glucose or amino acids)

• 95% of lipid in foods and body fat

phospholipids

one of the three main classes of dietary lipids

• phosphorus containing molecule + 2 fatty acids + 1 glycerol

• present in all cell membranes

• water and fat soluble

• emulsifier

• lecithin in egg yolk

emulsification

mixing lipid with water by adding an emulsifier

sterols

one of the three main classes of dietary lipids

• have similar structure to cholesterol

• interconnected rings of carbon atoms with side chains of C, H, and O attached

cholesterol

member of sterol group

• soft waxy substance made in the body for variety of purposes

• present in all cell membranes and bile

• precursor for vitamin D, sex hormones (estrogen, testosterone), stress hormones (epinephrine)

• makes bile

list the uses of fats in the body

• energy stores

• muscle fuel

• emergency reserve

• padding

• insulation

• cell membranes

• raw materials

list the use of fats in food

• nutrient

• energy

• transport

• raw materials

• sensory appeal

• appetite

• satiety

• texture

essential fatty acids

fatty acids that the body needs but can’t make in amounts sufficient to meet physiological needs

how are fatty acids classified

by chain length

• short < 10 carbons

• medium 12-14 carbons

• long >16 carbons

and degree of saturation

saturated fatty acid

carrying the maximum possible number of hydrogen atoms

• tend to be solid at room temp

• butterfat, coconut and palm oils

unsaturated fatty acid

fatty acid carbon chain that possesses one or more points of unsaturation (empty spot - hydrogen missing)

• tend to be liquid (oils) at room temp

• plant and fish oils

monounsaturated fatty acid

fatty acid containing one point of unsaturation

polyunsaturated fatty acid

fatty acid with two or more points of unsaturation

what happens to the lipids in the stomach

fat separates from watery components and floats as a layer on the top, little fat digestion by gastric lipase

what happens to the lipids in the small intestine

bile needed to emulsify lipid and chyme and fat digesting enzymes like pancreatic lipase splits them into smaller particles for absorption

what happens once the lipids are emulsified

fat splitting enzymes act on triglycerides to split fatty acids from their glycerol backbones

• gets shuttled by the bile across watery mucus layer to absorptive cells of intestinal villi

how do the smaller lipids get transported

glycerol and shorter chain fatty acids pass directly through the cells of the intestinal lining into the bloodstream where they travel unassisted to the liver

how do the larger lipids get transported

monoglycerides and long chain fatty acids must form lipoproteins before they can be released into the lymph that leads to the blood

• chylomicrons form one type of lipoprotein

lipoproteins

clusters of lipids associated with protein, serve as transport vehicles for lipids in blood and lymph

chylomicrons

dietary lipid and carrier proteins that transport fats through watery blood fluids

• produced in the intestinal cells

how much total fat is recommended DRI

20-35% of total calories

how much polyunsaturated fat is recommended by DRI

omego 6 linoleic acid: 5-10% of total calories

omega 3 linolenic acid: 0.6%-1.2% of total calories

very low density lipoproteins (VLDL)

carry triglycerides and lipids made in the liver to the body cells for their use

low density lipoproteins (LDL)

transport cholesterol and other lipids to the tissues (muscle, fat)

• made form VLDL

high density lipoproteins (HDL)

critical in the process of carrying cholesterol away from body cells to liver for disposal

what are the two lipoproteins that present major risk factors for heart disease

blood LDL and HDL concentrations

what fats raise blood cholesterol

most saturated food fats and trans fats raise blood cholesterol more than food cholesterol does

what are the top contributors to saturated fats in the canadian diet

beef, pork, lamb, goat mixed dishes, unflavoured milk, cheese, egg dishes, dairy desserts

how does someone lower LDL cholesterol

replace saturated fats with unsaturated fats in the diet

DRI for trans and saturated fat

as low as possible

what are the two essential fatty acids and what do they do

two polyunsaturated fatty acids

• linoleic acid (omega 6) and linolenic acid (omega 3)

used by the body to make eicosanoids - biologically active compounds that regulate body functions

list some of the roles of linoleic and linolenic acid

• raw material for eicosanoids

• structural and functional parts of cell membranes

• contribute lipids to the brain and nerves

• promote normal growth and vision

• assist in gene regulation

• maintain outer structures of the skin - protect against water loss

• regulate genetic activities affecting metabolism

• support immune cell functions

what are the consequences of a diet deficient in all polyunsaturated fatty acids

• skin lesions

• reproductive failure

• fatty liver

• kidney disorders

• reduced learning

• impaired growth

• imparied vision

what is omega 6, give example, DRI and sources

double bond six carbons from the end of the carbon chain

ex. linoleic acid (arachidonic acid - derived from linoleic acid)

dri: 5-10% energy from n-6 fatty acids

sources: vegetable oils, seeds, nuts, whole grain products

what is omega 3, give example, DRI and sources

double bond three carbons from the end of the carbon chain

ex. linolenic acid

DRI: 0.6-1.2% energy from n-3 fatty acids

sources: flaxseed, flaxseed oil, canola oil, fish

EPA and DHA and sources

eicosapentaenoic acid and docosahexaenoic acid - omega 3 fatty acids made from linolenic acid in the tissues of fish

• omega 3 enriched eggs, algae oils, fish and seafood

what are some potential benefits of EPA/DHA

• against heart disease - reduce abnormal blood clotting and inflammation

• mental health - prevent and treat depression, reduce risk of dementia

• against cancer - inhibit cancer development

what are the risks of consuming supplements of fish oil

• high intakes of omega 3 polyunsaturated fatty acids may increase bleeding time - interfere with wound healing, suppress immune function

• high levels of vitamin A and D. A=dangerous for pregnant people - interfere with normal fetal development

• fish skins may have accumulated toxic [ ]s of pesticides, heavy metals like mercury, other industrial contaminants

methylmercury

mercury escapes from industries, power plants into waterways where bacteria convert it into a highly toxic form. it then concentrates in the flesh of large predatory fish. cooking doesn’t diminish mercury concentrations

which fish species may accumulate the most mercury

• tuna

• shark

• swordfish

• escolar

• marlin

• orange roughy

what kind of fish should you consume (lower in mercury)

• shrimp

• canned light tuna

• salmon

• pollock

• catfish

hydrogenation

the process of removing carbon double bonds by adding hydrogen to unsaturated fatty acids to make them stay fresher longer

how is margarine made

they hydrogenate the polyunsaturated oil such as corn oil by forcing hydrogen into the liquid oil = more spreadable than the original oil

• prevents spoilage and make them harder and more stable when heated to high temps

trans fatty acids

fatty acids with unusual shapes that can arise when polyunsaturated oils are hydrogenated

• required on food labels

what kind of fat did health canada ban

partially hydrogenated oils

what percentage of fat is required from the total daily calories

33 percent of total daily calories