HNSC UNIT 5

Lipids

Lipids: The Basics

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

Polyunsaturated Fatty Acids - DRI

• 5-10% from linoleic acid (omega 6)

• 0.6-1.2% energy from linolenic acid (omega 3)

Cholesterol - DRI

• DRI: minimize intake within context of healthy diet

• only about 1/3 population responds to lowering dietary cholesterol intake

• limit eggs, shellfish, liver, etc. but these are also nutritious foods

Classification of Lipids - Triglycerides

• 95% of lipid in foods and body fat

• 3 fatty acids + glycerol backbone

• glycerol is made from glucose or amino acids

Fatty Acids Chain Lengths

• short: less than or equal to 10 carbons

• medium: 12-14 carbons

• long: more or equal to 16 carbons

• shorter chain FAs tend to be softer and melt more readily at room temp

Fatty Acids by Degree of Saturation

• saturated: no double bonds

  • tend to be solid at room temp (butterfat)

• monosaturated: 1 double bond

  • canola and olive oils

• polyunsaturated: 2+ double bonds

  • tend to be liquid at room temp (plant, fish oils)

Margarines: Hydrogenation

• removing C=C double bonds by adding hydrogen

  • veg. oil → “hard” margarine

  • better storage/less rancidity and high smoke point for frying

  • creates trans-fatty acid which act like saturated fatty acids in the body (increases risk of cardiovascular disease)

Margarines: Trans Fatty Acids

• food labels require a separate category

• 2018: health Canada banned partially hydrogenated oil in foods

• blending different oils to produce a “soft” margarine

Phospholipids

• glycerol backbone + 2 fatty acids + phosphorus containing molecule

• water and fat soluble

• can serve as emulsifier

• e.g. lecithin in egg yolk - no special health promoting abilities

Sterols

• cholesterol: present in cell membranes and bile

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

Lipid Digestion in the Stomach

• fats separates from watery components and floats to top

• little fat digestion

Lipid Digestion in the SI

• bile needed to emulsify lipid and chyme

• pancreatic lipase (enzyme) to split into smaller particles

Lipid Absorption

• small lipids (short and medium chain FAs and glycerol) enter capillary network → bloodstream

• large lipids (long chain FAs and monoglycerides [glycerol+1 fatty acid]) travel in bloodstream as chylomicrons

Lipid Transport - Chylomicrons

• dietary lipid and carrier proteins → transports fats through watery blood fluids

Lipid Transport - Very Low Density Lipoprotein

• transport triglycerides and lipids synthesized in liver → body cells

Lipid Transport - Low Density Lipoprotein

• transports lipids and cholesterol → body cells (muscle, fat)

Lipid Transport - High Density Lipoprotein

• return cholesterol in body cells → liver for excretion

Lipid Metabolism

• when body starts to run out of fuel from food, turns to body stores

• FAs are used for energy by many organs: typical fuel mix is 50/50 carb/lipid for liver and muscle (at rest)

• any time fat broken down for energy, CHO must be available

  • ketones develop and build up in urine and blood

Major Risk Factors for Heart Disease

• high LDL cholesterol

• low HDL cholesterol

• a diet high in saturated and trans fats, and low in veggies, fruits, whole grains

Cholesterol

• 75-80% is synthesized in the body (drugs to inhibit synthesis)

• stimulation of synthesis by saturated fats

• dietary cholesterol plays a lesser role than saturates and trans fats in cardiovascular disease

• ~60% exhibit little increase in blood cholesterol with high cholesterol diet

Essential Fatty Acids

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

  • the only fatty acids that cannot be synthesized by body

  • essential nutrients

  • polyunsaturated fatty acids

  • used by the body to make eicosanoids

  • regulate body functions

EFA Deficient Diet Symptoms

• skin lesions

• reproductive failure

• fatty liver

• kidney disorders

• reduced learning

• impaired growth and vision

Omega-6

• C=C 6 carbons from end

  • linoleic acid

• DRI: 5-10% energy from n-6 fatty acids

• sources: veg. oils, seeds, nuts, whole grain products

Omega-3

• C=C carbons from end

  • linolenic acid

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

• sources: flaxseed, canola oil, fish (deep seas fish)

• need more n-3 in our diet to prevent heart disease

• 2-3 meals of fatty fish per week

• fish is more beneficial than supplements

Potential Benefits of EPA/DHA

• heart disease (supported by most studies)

• mental health and cognition

• cancer

Major Dietary Sources of Fat

• dairy products (excluding milk and butter)

• processed meat

• margarine

• cooking oils

• bakery products

• butter

• fresh meats

• fluid milk

  • all are sources of saturated fats except cooking oils

Fat Replacers

• alter preparation method:

  • add water or whip air into foods

  • add non-fat milk to creamy foods

  • use lean products vs high fat

  • bake rather than fry

Present Guidelines

• replace saturated fats with unsaturated fats to help lower cholesterol

• specifically polyunsaturated fats are effective

• avoid trans-fats