BIO-319 quiz 3

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Four characteristics of protein

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Four characteristics of protein

  • large, complex molecules

  • found in cells of all living things

  • organic molecule

  • composed of long chain of amino acids (20)

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Amino acid structure

  • each have the same basic structure

  • carbon atom (alpha carbon) with:

    • amino group (NH2)

    • Carboxylic acid (COOH)

    • H atom

    • Side chain (R group)

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How are amino acids linked together

peptide bonds

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2 amino acids

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3 amino acids

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more than 3 amino acids

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70 or more amino acids

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What is protein denaturation

  • proteins uncoil and lose their shape

  • protein function is lost (shape=function)

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what causes protein denaturation

  • temperature

  • pH

  • enzymes

  • alcohol

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Essential amino acids

  • cannot be produced in sufficient quantities to meet physiological needs

  • must be obtained from food

  • total of 9 essential amino acids

  • support normal body growth-maintenance repair

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Non-essential amino acids

  • can be synthesized by the body in sufficient quantities

  • Total of 11 non-essential amino acids

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Conditionally essential amino acids

  • non-essential amino acid become essential in the diet

  • phylketonuria (PKU): tryosine becomes a conditionally essential amino acid

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  • transfer amine group (NH2) from essential amino acid to a different acid group and R group

  • used to make nonessential amino acids

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How do we determine protein quality ?

  • determine how well a protein from food matches the body’s requirements and, therefore, how useful the protein is for our body

    • amino acid composition

    • protein digestibility

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Amino acid composition: complete proteins

  • contain all 9 essential amino acids

  • adequate amounts for growth and maintenance of body tissue

  • all animal products are complete proteins except gelatin

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Amino acid composition: incomplete proteins

  • lack one or more of the 9 essential amino acids

  • cannot support either maintenance or growth of body tissues

  • most of the plant proteins are incomplete

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amino acid composition: partially complete protein

  • contains all 9 essential amino acids, but one or more is limited

  • limiting amino acid

  • limits the amount that all amino acids can be used to produce protein

    • can support maintenance but not growth of tissues

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Limiting amino acids

an essential amino acid supplied in less than the amount needed to support protein synthesis

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Amino acid composition: complementary protein

  • combining two incomplete protein sources

  • amino acids in one food makeup for those lacking in the other food

  • vegetarian must mix protein-rich plant foods to get amino acid balance, ex.- rice and beans

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Protein digestibility

  • digestibility of a protein varies between foods

  • amino acids from animal sources are digested more easily

    • animal proteins: 90-99% digested and absorbed

    • plant proteins: 70-90% digested and absorbed

    • Soy and legumes: >90% digested and absorbed

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protein quality: reference proteins

  • a standard against which to measure the quality of other proteins

  • compares amino acid composition with essential amino acid requirements of preschool-age children

  • Reference proteins:

    • highest protein quality and digestibility

    • sustain maximal growth rates

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Protein quality: biological value (BV) (high and low)

  • nitrogen is retained/ absorbed

  • high biological value

    • more nitrogen is retained/ absorbed

    • generally animal proteins (Ex. eggs)

  • Low biological value

    • less nitrogen is retained/ absorbed (more is exerted)

    • generally plant proteins

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Protein function

  • growth and maintenance

  • body processes

  • energy

  • fluid and electrolyte balance

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Protein function: growth and maintenance

  • involved whenever body is growing, repairing, or replacing tissues

  • form the building blocks of muscles, blood, and skin

  • collagen is a structural protein that makes scars, tendons, ligaments, foundations of bones and teeth

  • replace dead cells → avg. life span of skin cell 30 days and cells of GI tract are replaced every few days

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Protein function: body processes

  • enzymes→ digestion, DNA synthesis

  • hormones→ messenger molecules that tell something to happen (insulin, glucagon)

  • antibodies→ large proteins that are produced by your immune system to fight viruses

  • transport proteins→ brining important substances in and out of your cells, lipoproteins

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Protein function: energy

  • they are sacrificed to provide energy and glucose during times of starvation or insufficient carb intake

  • tissue proteins are broken down to make amino acids available for energy or glucose production- known as GLUCONEOGENESIS

  • protein can maintain blood glucose levels, but at the expense of losing lean body tissue

  • 4 kcal per gram

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Protein function: fluid and electrolyte balance

  • protein attracts water, protein in the blood creates an osmotic pressure and keeps fluid from seeping out into extracellular space

  • during critical illness or protein malnutrition, plasma proteins can leak out of the blood vessels into the spaces between the cells

  • due to protein attracting water, fluid can accumulate and cause swelling (edema)

  • also accepts and releases hydrogen ions, thus acting as buffers in the blood- maintaining acid- base balance - pH balance

  • failure of any part of the fluid balance system causes edema (protein deficiency)

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Sickle cell disease

  • two of hemoglobin’s four polypeptide chains have a normal sequence of amino acids, but the other chains do not

  • changes shape of hemoglobin

  • loses its ability to carry oxygen effectively

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Protein digestion: where?

  • stomach: <10% of protein is digested

  • small intestine: >90% of protein is digested

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protein digestion: how?

  • stomach: pepsin and HCl (acid)

  • small intestine: chymotrypsin and trypsin

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Protein digestion

  • protein foods denatured by stomach acids (HCl)

  • enzymes from stomach, pancreas, and small intestine digest proteins

  • free amino acids are formed

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Protein absorption

  • amino acids absorbed by villi

  • delivered to cells via blood

  • amino acids rebuilt as needed into new protein in the cells

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Protein balance

  • balance of protein output and protein intake

  • nitrogen balance: the amount of nitrogen consumed compared to the amount of excreted in a given time period

    • equilibrium or nitrogen balance: intake = output

    • positive nitrogen balance: intake > output

    • Negative nitrogen balance: intake < output

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protein balance: positive nitrogen balance

  • growth (infant and children)

  • pregnancy and lactation

  • recovery from illness

  • athletes

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protein balance: negative nitrogen balance

  • when muscles or other protein tissue breaks down and is lost (illness

  • inadequate protein intake (fasting)

  • inadequate energy intake

  • deficiency in essential amino acids

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RDA protein requirement

0.8 grams per kg healthy body weight

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AMDR protein requirement

10-35% total kcals

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  • protein malnutrition, disease resulting from low protein intake

  • occurs often when child taken off breast milk and fed starchy liquid

  • usually develops rapidly

  • will cause symptoms of EDEMA→ swollen belly

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  • protein-energy malnutrition

  • extreme starvation; occurs during famine, especially in infants

  • resulting from chronic underfeeding, both inadequate energy as well as protein

  • symptoms:

    • weakening of the muscles

    • stunted brain development and learning

    • depressed metabolism

    • stunted physical growth

    • growth ceases

    • death

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Excessive protein intake

  • often associated with obesity

  • high cholesterol and heart disease

  • contribution to bone loss

  • kidney disease

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Triglycerides (TG)

  • fats and oils

  • 90-95% lipids in food

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2-3% lipids in food

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2-7% lipids in food

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types of lipids

  • triglycerides

  • phospholipids

  • sterols

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Triglycerides basic structure

  • glycerol backbone

  • 3 fatty acids

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Fatty acid structure

  • C-H chain

  • COOH (acid group)

  • CH3 (methyl group)

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fatty acid differences

  • length of carbon chain

  • number of double bonds

  • location of double bonds

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Fatty acid differences: length of carbon chain

  • most contain even number of carbons- up to 24

  • long chain fatty acids

    • 12-24 carbons

    • meats, seafood, vegetable oils

    • most common in diet

  • Medium- chain fatty acids

    • 6-10 carbons

  • Short-chain fatty acids

    • less than 6 carbons

  • medium and short primarily in dairy products

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Fatty acids differences: number of double bonds→ saturated fatty acids

  • carbon is “saturated” with hydrogens

  • no double bond

  • solid at room temp

  • primarily from animal sources

  • some plant sources

  • associated with health risks

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Fatty acids differences: number of double bonds→ unsaturated fatty acids

  • carbon lacks hydrogen atoms

  • at least one double bond between carbons

  • point of unsaturation

  • liquid at room temperature (oils)

  • primarily from plant sources

  • double bonds are “reactive”

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Monounsaturated fatty acids

  • one double bond

  • “cis” formation

  • sources: olive, peanut, canola oils

    • mediterranean diet

  • usually omega-9 group

    • only double bond 9 carbons from methyl end

  • oleic acid (18 carbons, omega 9)

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polyunsaturated fatty acids

  • two or more double bonds

  • “cis” formation

  • two basic forms

    • Linoleic acid→ Omega 6

    • Linolenic acid→ Omega 3

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polyunsaturated fatty acid: omega-6

  • omega 6= linoleic acid

  • 18 carbon chain

  • two double bonds

  • essential in our diet

  • sources: vegetable oils, nuts, poultry

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polyunsaturated fatty acid: omega-3

  • omega 3= linolenic acid

  • 18 carbon chain

  • three double bonds

  • EPA (food form, essential)

    • may lower cholesterol and decrease risk of heart disease, HTN, cancer, arthritis

    • reduce inflammation, blood clotting, plasma TG

    • sources: vegetable oils, nuts, poultry

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Fatty acids differences: location of double bonds

identified by closest double bond to methyl end of the carbon chain

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characteristics of fats

  • lipids that are solid at room temperature

    • most saturated animal fats

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characteristics of oils

  • lipids that are liquid at room temperature

    • most unsaturated plant fats

    • cocoa butter, palm oil, palm kernel oil, coconut oil have higher saturated fat content

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characteristics of fats and oils: degree of unsaturated affects stability

  • spoiled (rancid) when exposed to oxygen

  • polyunsaturated fats spoil most readily- double bonds are unstable

  • saturated fats least likely to turn rancid

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characteristics of fats and oils: manufacturers protect fat-containing products

  1. air-tight containers, protected from light, refrigerated

  2. antioxidant additives

  3. hydrogenation-cis→ trans fatty acids

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  • the process of adding hydrogen to double bonds

  • converts double bonds → single bonds

  • may be partially or fully hydrogenated

  • makes oils more solid and more saturated

  • improves shelf life

  • increases risk of cardiovascular disease

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hydrogenation pros

  • decrease food spoilage

  • can use oils as solid fats

  • better cooking qualities

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hydrogenation cons

  • increase saturation of fats

  • produce trans fats

  • “unnatural” reaction

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triglycerides and condensation reaction

  • few fatty acids occur free in foods or in the body

  • most are incorporated into triglycerides

  • most contain a mixture of more than one type of fatty acid

  • formed via condensation reactions

    • H from glycerol + OH from fatty acid → triglyceride + H2O

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  • two fatty acids +glycerol

  • generated during digestion of triglycerides

  • added to foods as an emulsifier

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  • one fatty acid +glycerol

  • also generated during digestion and used as emulsifier in foods

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Phospholipid structure

  • glycerol backbone

  • two fatty acids

  • phosphorus-containing side group

  • polar head and nonpolar tail

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phospholipids manufactures in our bodies

not essential in our diet

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phospholipid functions

  • major component of cell membranes

  • important transport forms of lipids in the blood

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best known phospholipid


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phospholipid supplements not needed

  • can cause GI distress, loss of appetite

  • liver makes phospholipids for the body

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phospholipid food sources

eggs (yolks only), liver, soybean, wheat germ, peanuts

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sterol structure

multi-ring structure

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most well known sterol


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sterols are in foods derived from ____

  • plants/ animals

  • plant sterols interfere with cholesterol absorption and lower blood cholesterol levels

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cholesterol is in foods derived from ____

  • animals only

  • body can make all the cholesterol we need; no dietary requirement

  • associated with heart disease

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Sterol function

  • bile acids

  • sex hormones (testosterone, androgen, estrogen)

  • vitamin D

  • adrenal hormones (cortisol, cortisone, aldosterone)

  • cholesterol is structural component of cell membranes

    • more than 90% of all body’s cholesterol is found in cells

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Cholesterol sources

  • endogenous (made by the liver)→ up to 1500 mg/day

  • exogenous (from animal food)→ 200-300 mg/day

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the role of lipids in diet

  • energy source

  • essential fatty acids

  • carrier of fat-soluble vitamins

  • palatability

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the role of lipids in the body

  • energy reserve

  • insulates to prevent loss of body heat

  • regulates body functions

    • cell membrane structure and activity

    • precursor of hormone-like substances (eicosanoids)

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Fat absorption: glycerol and short/medium-chain fatty acids

  • absorbed into blood

  • go directly to liver

  • made into VLDL (form of lipoprotein)

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Fat absorption: monoglycerides and long-chain fatty acids

  • form micelles in the small intestine

  • absorbed into small intestinal cells

  • repackaged into new TG

  • packed into chylomicrons

  • chylomicrons enter lymph

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how to differentiate Saturated and unsaturated fatty acids

  • Saturated will be saturated with hydrogen

  • unsaturated will have double bonds

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clusters of lipids, proteins, cholesterol, and triglycerides that act as “transport vehicles” for fats

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Four different types of lipids in order from largest and least dense to smallest and most dense

  1. Chylomicrons

  2. Very low density lipoproteins (VLDL)

  3. Low density lipoproteins (LDL)

  4. High density Lipoproteins (HDL)

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  • transport dietary lipids (mostly triglycerides) from the small intestine to the rest of the body (via lymph system)

  • Cells remove triglycerides from chylomicrons as they pass by, so they get smaller and smaller

  • once TG are depleted, only few remnants of protein, cholesterol, and phospholipids remain

  • liver removes chylomicron remnants from blood

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  • lipids made in the liver and collected from chylomicron remnants are packaged with protein → VLDL

  • VLDL delivers cholesterol and fatty acids to needy cells

    • Density increases as fat leaved VLDL

    • VLDL becomes LDL

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  • high in cholesterol

  • circulates through the body delivering triglycerides, cholesterol, and phospholipids to cells

  • liver removes LDL from circulation

    • controls blood cholesterol concentrations

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  • liver makes HDL

  • removes cholesterol from cells and carries it back to liver for cycling or disposal

  • can pick up cholesterol from plaques

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good cholesterol

  • HDL

    • lowers risk of heart disease

    • anti-inflammatory properties

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bad cholesterol

  • LDL

    • contributes to plaques when cholesterol “falls off” the LDL and is deposited on artery walls

    • plaques narrow arteries → increases blood pressure → increases risk of blood clots/ heart attacks

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disease associated with lipids

  • blood pressure

  • cardiovascular disease

  • obesity

  • cancer

  • diabetes

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diets high in saturated fats

  • decrease removal of LDLs from the blood

  • increase blood cholesterol levels

  • formation of plaques that can block arteries

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diets high in trans fats

  • raise LDL as much as saturated fat

  • abundant in hydrogenated vegetable oils

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How to lower LDL-C to reduce risk of CVD


  • reduce cholesterol intake

  • eliminate trans fats

  • increase omega-3

  • increase fiber

  • physical activity

  • other lifestyle changes:

    • normal blood glucose levels

    • eat throughout day

    • maintain active lifestyle

    • maintain healthy body weight

    • decrease salt intake

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How to increase HDL-C

  • exercise

  • increase fiber

  • increase fruit/vegetable consumption

  • smoking cessation

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Mediterranean diet

  • high in omega-3/omega-6

  • high in fiber

  • high in poly/monounsaturated fats

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Food sources of fat: visible fats

  • visible fats

    • added to foods

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Food sources of fat: invisible fats

  • Invisible fats

    • hidden within foods

    • occur naturally or added during processing

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Food sources of fat: beneficial fats

  • omega-3 fatty acids may be low in current diet

  • add more: fish, walnuts, soy, canola, flaxseed

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Food sources of fat: fat replacers

  • used to lower fat content of foods

  • found in chips, cakes, cookies

  • may cause GI side effects in large amounts

  • example: olestra (olean)

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