Lipids - Chapter 5

Question 1

Lipids

Answer 1

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

Question 2

Recommendations for Dietary Fat

Answer 2

• Polyunsaturated fatty acids - DRI:
  ◦ 5-10% energy from linoleic acid (omega 6)
  ◦ 0.6-1.2% energy from linolenic acid (omega 3)
• Cholesterol:
  ◦ 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

Question 3

Classification of Lipids (1)

Answer 3

• Triglycerides
  
  • 95% of lipid in foods and body fat
  • 3 fatty acids + glycerol backbone
  • Glycerol is made from glucose or amino acids

Question 4

Classification of Lipids (2)

Answer 4

• Fatty acids classified by chain length
  
  • Short: < 10 carbons
  • Medium: 12-14 carbons
  • Long: > 16 carbons
• Shorter chain FAs tend to be softer and melt more readily at room temperature

Question 5

Classification of Lipids (3)

Answer 5

• Fatty acids classified by degree of saturation
  
  • Saturated: no double bonds
    
    • Tend to be solid at room temp.
    • Ex: butterfat, coconut & palm oils
• Monounsaturated: 1 double bond
  
  • Ex: canola & olive oils
• Polyunsaturated: 2+ double bonds
  
  • Tend to be liquid (oils) at room temp.
  • Ex: plant & fish oils

Question 6

Effects of processing on Saturated Fats

Answer 6

• Margarines
  
  • Hydrogenation: removing C=C double bonds by adding
    hydrogen
    
    • Vegetable oil → “hard” margarine, hydrogenated shortening)
    • 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)

Question 7

More on Margarines

Answer 7

• 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”
  
  • E.g., Becel and other non-hydrogenated products

Question 8

Other lipids (1)

Answer 8

• 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

Question 9

Other Lipids (2)

Answer 9

• Sterols
  
  • Cholesterol: present in cell membranes and bile
    
    • Precursor for vitamin D, sex hormones (estrogen, testosterone), stress hormones (epinephrine)

Question 10

Lipid Digestion (1 Stomach)

Answer 10

• In the stomach:
  
  • Fat separates from watery components and floats to top
  • Little fat digestion

Question 11

Lipid Digestion (2 Small Intestine)

Answer 11

• In the small intestine:
  
  • Bile needed to emulsify lipid and chyme
  • Pancreatic lipase (enzyme) to split into smaller particles

Question 12

Lipid Absorption

Answer 12

• 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

Question 13

Lipid Transport

Answer 13

• Lipoproteins
  
  • Chylomicrons: dietary lipid and carrier proteins  transport fats through watery blood fluids
  • Very low density lipoprotein (VLDL): transport triglycerides and lipids synthesized in liver body cells
  • Low density lipoprotein (LDL): transports lipids and cholesterol body cells
    (muscle, fat)
  • High density lipoprotein (HDL): return cholesterol in body cells liver for excretion

Question 14

Lipid Metabolism

Answer 14

• 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
  carbohydrate/lipid for liver and muscle (at rest)
• Any time fat broken down for energy, CHO must be available
  
  • Otherwise, ketones develop (products of incomplete fat breakdown) and build up in blood and urine

Question 15

Blood Cholesterol & Cardiovascular Disease
Risk

Answer 15

• High LDL-cholesterol increases risk for heart disease
• Major risk factors for heart disease:
  
  • High LDL cholesterol
  • Low HDL cholesterol
  • A diet high in saturated and trans fats, and low in vegetables, fruits, and
    whole grains
• Diet (low fat & antioxidant nutrients) and lifestyle factors important

Question 16

Cholesterol

Answer 16

• Cholesterol has precursor and structural roles; required for health
• 75-80% is synthesized de novo (in the body)
  
  • Drugs to inhibit synthesis
• Stimulation of synthesis by saturated fats
• Dietary cholesterol plays a lesser role than saturated and trans fat in cardiovascular disease
• ~60% exhibit little increase in blood cholesterol with high cholesterol diet

Question 17

Essential Fatty Acids
(EFAs)

Answer 17

• Linoleic acid (omega-6) and Linolenic acid (omega-3)
  
  • 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

Question 18

EFAs

Answer 18

• When diet deficient in all polyunsaturated fatty acids (PUFAs):
  
  • Skin lesions
  • Reproductive failure
  • Fatty liver
  • Kidney disorders
  • Reduced learning
  • Impaired growth
  • Impaired vision
• Deficiency rare: body stores some extra

Question 19

Omega-6

Answer 19

• C = C 6 carbons from end
• Ex: Linoleic acid
• DRI: 5-10% energy from n-6 fatty acids
• Sources: vegetable oils, seeds, nuts, whole grain products

Question 20

Omega-3 (1)

Answer 20

• C = C 3 carbons from end
• Ex. Linolenic acid
• DRI: 0.6-1.2% energy from n-3 fatty acids
• Sources: flaxseed, flaxseed oil, canola oil, fish (especially deep sea fish)

Question 21

Omega-3 (2)

Answer 21

• N.B. ratio of n-6/n-3: need more n-3 in our diet (like
  ancestors) to prevent heart disease
• Recommendation: 2-3 meals of fatty fish per week to improve heart health
• EPA/DHA content reduced in fried fish
• Studies: fish more beneficial than supplements

Question 22

Potential Benefits of EPA/DHA

Answer 22

• Heart disease (supported by most studies)
• Mental health and cognition
• Cancer (research promising, but need further evidence)

Question 23

Weighing Seafood’s Risks and Benefits (1)

Answer 23

• Mercury contaminated fish
  
  • Generally low levels of mercury contaminate most fish species
  • It is yet to be established just how much mercury worsens preexisting heart disease
• Fish heavily contaminated with mercury
  
  • Shark
  • Swordfish
  • King mackerel
  • Fresh tuna steak (Albacore)
  • Tilefish

Question 24

Weighing Seafood’s Risks and Benefits (2)

Answer 24

• Fish/seafood lower in mercury
  
  • Shrimp
  • Canned light tuna (canned albacore [“white”] tuna contains more
    mercury than light tuna)
  • Salmon
  • Pollock
  • Catfish

Question 25

Weighing Seafood’s Risks and Benefits (3)

Answer 25

• Recommendations
  
  • Consume a variety of fish
    
    • Minimizes exposure to any particular toxin that may accumulate in a
      particular fish species
• Pregnant individuals and children
  
  • Most sensitive to the side effects of mercury
  • Can safely benefit from safer fish varieties within recommended limits

Question 26

Major Dietary Sources of Fat

Answer 26

• Dairy products (excluding
  milk & butter)
• Processed meat
• Margarine
• Salad and cooking oils
• Bakery products
• Fresh meats
• Butter
• Fluid milk
• *All except salad and
  cooking oils are sources of
  saturated fat

Question 27

Dietary Fat: g, %
Calories

Answer 27

• Ice cream (1 cup=357 Cal) 24 g, 61%
• Ice milk (1 cup=182 Cal) 6 g, 30%
• Cheddar cheese (50 g=205 Cal) 16 g, 70%
• Low fat mozzarella (50 g=142 Cal) 9 g, 57%
• Wiener for hot dog (2=360 Cal) 32 g, 80%
• Lean beef (4 oz=250 Cal) 11 g, 40%
• Macaroni & cheese (1 c=430 Cal) 22 g, 46%
• Spaghetti & tomato sauce (1c=260 Cal) 9 g, 31%

Question 28

Food Feature: Defensive Dining

Answer 28

• Substitutes for
  high-fat ingredients
• Fast Food Choices
• Saturated Fat
  Replacements
• Choosing Unsaturated Fats Instead of Saturated Fats

Question 29

Fat Replacers

Answer 29

• Fat replacers and artificial fats
• Alter preparation method, for example:
  
  • Add water or whip air into foods
  • Add non-fat milk to creamy foods
  • Use lean products vs. high fat
  • Bake rather than fry

Question 30

Controversy 5: Is butter back? The Lipid Guidelines Debate (1)

Answer 30

• Lots of consumer advice in the public media
• Often controversial
• Goals: prevention of cardiovascular diseases
• Role of saturated fats discussed
• Strong scientific evidence for diet low in saturated fat

Question 31

Controversy 5: Is butter back? The Lipid Guidelines Debate (2 Historic Guidelines)

Answer 31

• Cut total fat intake for cardiovascular disease prevention
• However, replacement of fats with sugars lead to negative health outcome
• E.g., increased diabetes and CVD
• Guidelines evolved with new evidence

Question 32

Controversy 5: Is butter back? The Lipid Guidelines Debate (3 Milestone Research)

Answer 32

• Seven Countries Study of healthy people
  
  • Death rates from heart disease strongly associated with diets high in saturated fats
  • Death rates from heart disease were weakly associated with diets high in total fat
  • Finland and Crete were the two countries with the
    highest fat intake
    
    • Finland had the highest rate of death from heart
      disease
    • Crete had the lowest rate of death from heart disease
  • Relative to Finland, people in Crete had a diet
    
    • High in olive oil
    • Low in saturated fat (<10% of calories)

Question 33

Controversy 5: Is butter back? The Lipid Guidelines Debate (4 Present Guidelines)

Answer 33

• Replace saturated fats with unsaturated fats
• Specifically polyunsaturated fats are effective
• Avoid trans-fats
• When replacing saturated fats with polyunsaturated:
  
  • Every 1% reduction in calories from saturated fatty acids → leads to → 2 to 3% reduction in CVD

Question 34

Controversy 5: Is butter back? The Lipid Guidelines Debate (5 Health Canada Approved Health Claim)

Answer 34

Rplacing saturated fats with polyunsaturated and monounsaturated fats (from vegetable oils) helps lower/reduce cholesterol

Question 35

Controversy 5: Is butter back? The Lipid Guidelines Debate (6 There is debate)

Answer 35

• Biological mechanism underling the beneficial
  effects are unknown
• Role of the genetic background unknown
• Actions of specific FAs undetermined
• Some saturated fats might not be detrimental
• Oversupply of some polyunsaturated fats might
  be detrimental

Question 36

Controversy 5: Is butter back? The Lipid Guidelines Debate (7 Controversy on Butter)

Answer 36

• Meta-analysis failed to correlate dietary saturated fat intake with the prevention of CVD
• This meta-analysis was heavily criticized
• Design limitations became apparent

Question 37

Controversy 5: Is butter back? The Lipid Guidelines Debate (8 What is right?)

Answer 37

• We cannot eat counting individual FA species
• Beneficial “Portfolio diets” emerged:
  
  • A health vegetarian diet
  • A healthy American (Canadian?) style diet
  • The classic Mediterranean diet