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Human Nutrition - Y2S1 > Dietary Fats + Lipids > Flashcards

Dietary Fats + Lipids Flashcards

1
Q

What’s the energy source from fats? (kcal)

A

1g of fat = 9kcal of energy

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2
Q

What are the 5 essential functions of fat in the body

A
  1. Cell membrane function - integral to membranes + cholesterol synthesis
  2. Protects vital organs - cushioning
  3. Critical for growth + development - supports functions of brain, eyes + heart
  4. Energy storage + insulation - adipose tissue stores + releases energy as needed + helps regulate body temp
  5. Absorption of fat-soluble vitamins
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3
Q

What is the function of dietary fats + recommendation intake of total EI?

A

Provides essential fatty acids

  • government recommends that total fat intake should not exceed 35% of total daily EI
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4
Q

What is the main form of fats in foods?

A

Triglycerides

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5
Q

What are the different triglycerides found in foods?

A
  1. Visible fats - concentrated fats (butter + veg oil) + marbling of fat in meat
  2. Hidden fats - baked goods, dairy products + fried food
  3. Naturally occurring triglycerides - avocados, olives, corn + nuts
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6
Q

What’s the simple structure of fats (triglycerides)

A

Each triglyceride molecule is made up of…

  • a molecule of glycerol + 3 fatty acids
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7
Q

Describe the structure of fatty acids

A

Made up of…

  1. A hydrocarbon chain - chain of carbon atoms bonded to hydrogen atoms (usually even numbers + insoluble in water)
  2. Carboxyl group (-COOH) - at one end of molecule (acidic end) - bound to glycerol
  3. Methyl group (CH3) - at other end
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8
Q

What factors affect fatty acid structure + physical properties?

A
  1. Chain length
  2. Number of double bonds
  3. Position of double bonds (n-3, n-6 etc)
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9
Q

What are the different number of double bonds called?

A
  1. Saturated - 0 double bonds
  2. Monounsaturated - 1 double bonds
  3. Polyunsaturated - >1 double bonds
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10
Q

What’s the impact of the physical properties of fats on health?

A

Melting point - determines whether fat is a liquid or solid at room temp

Health effects - how they effect blood cholesterol levels
- saturated + trans-fats (unsaturated) raise LDL cholesterol

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11
Q

What are the different classifications of fatty acids?

A

By number of carbons in chain

By number of carbon double bonds

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12
Q

How can fatty acids be classified by number of carbon atoms in chain?

A
  1. Short chain - <6 carbons (can be produced by gut bacteria during fermentation of dietary fibres, also found in fermented foods - kefir, yoghurt + cheese)
  2. Medium chain - 6-10 carbons (coconut oil, some dairy products)
  3. Long chain - >12 carbons (dairy, meat, fish, plant oils, nuts + seeds)

usually even number of carbons in chain (rare to find odd)

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13
Q

How can fatty acids be classified by number of carbon double bonds?

A
  1. Saturated - can tightly pack on glycerol back bone (solid at room temo)
  2. Monounsaturated
  3. Polyunsaturated - double bonds creates a kink causing loose packing on glycerol backbone (liquids at room temp)
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14
Q

What are the different culinary fats and oils?

A

Vegetable / plant oils

Animal fats

Tropical oils

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15
Q

Explain what vegetable oils are - state at room temp, type of fatty acids etc

A

They are liquid at room temperature

Mainly monosaturated but does have some saturated

Some omega-3 and omega-6

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16
Q

Explain what animal fats are - state at room temp, type of fatty acids etc

A

Solid at room temperature

Long chain saturated fatty acids mainly

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17
Q

Explain what tropical are - state at room temp, type of fatty acids etc

A

Coconut + palm oil (somewhere in between animal + veg)

Produce liquid at room temp due to containing some medium-length carbon chains

More solid than plant oils though - as medium length chains overrides effect of saturation (plant oils have a more unsaturated profile)

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18
Q

How would you name a fatty acid - what’s its based on?

A

Represented by counting from the methyl group e.g.

  • Carbon chain length = 18
  • No. double bonds = 1
  • (if applicable) position of first double bond = 9 carbons from methyl end

Therefore name = 18:1n-9

(an omega prefix ‘ꞷ-9’ can also be used instead of ‘n-9’)

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19
Q

How is digestion + absorption different for fats?

A

Triglycerides are non-polar (hydrophobic) so do not mix well with water

  • Therefore digestion + absorption is more complex
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20
Q

What are the key process of fat digestion + absorption?

A
  1. Stomach
  2. Emulsification of lipids in small intestine
  3. Enzymatic digestion by lipase in small intestine
  4. Absorption of fat digested products
  5. Absorption into blood stream
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21
Q

Describe what occurs to fats in the stomach

A
  1. Lingual lipase is released from saliva + initially active in mouth
  2. Then moves down into stomach, whereby acidic environment fully activates lipase
  3. Gastric lipase produced by chief cells are released + involved in fat digestion
  4. They break down fat molecules into diglycerides + fatty acids
  5. Most digestion occur later however (lipase only acts on 30% of fats in adults)
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22
Q

Describe emulsification of fats in the small intestine

A
  1. Lipid droplets are broken down into smaller, emulsified fat droplets
  2. Bile salts (released from gall bladder) help emulsify large lipid droplets
  3. Increased SA so digestive enzymes can access lipid droplets easier
23
Q

Describe enzymatic digestion of fats by pancreatic lipase in small intestine

A
  1. Pancreases releases pancreatic lipase into small intestine
  2. These help breakdown triglycerides further
  3. Breaks it down into monoglycerides + fatty acids
24
Q

Describe the absorption of fat digested products

A
  1. Micelles transport fat products to intestinal cell membranes for absorption
  2. Fatty acids + monoglycerides then diffuse from micelles across cell membranes into enterocytes (small intestine)
25
Q

Once monoglycerides + fatty acids are in enterocytes, where do they go?

A
  1. Short + medium chain fatty acids - can be absorbed directly into bloodstream
  2. Long chain fatty acids + monoglycerides - reassemble triglycerides within intestinal cells + incorporated into chylomicrons (lipid transport vesicles)
  • then taken to tissues such as liver
26
Q

What’s the fate of absorbed lipids?

A
  1. Liver plays a role in fat metabolism - synthesises lipoproteins, cholesterol + phospholipids for body functions
  2. Metabolic fate of lipids depends on dietary intake + energy needs
  • Excessive fat intake - liver converts excess fat for storage in subcutaneous tissue via lipogenesis
  • If energy + glucose levels are lower - stored fat is broken down into glycerol + fatty acids via lipolysis for energy use
27
Q

What are the key fat-soluble vitamins + what’s required for their absorption?

A

Vitamin A, D, E and K

  • they absorb better when consumed with dietary fat
28
Q

What’s the function of Vitamin A (retinol)?

Give some examples of foods

A
  • contributes to immune system (normal function)
  • helps with vision in dim light
  • helps keep skin + linings of some parts of body (nose) healthy

Whole milk, cheese, carrots, dark green leafy veg + orange fruit

29
Q

What’s the function of Vitamin D?

Give some examples of foods

A
  • helps keeps bones healthy
  • lack of vitamin D can lead to bone deformities (such as rickets in children)

Oily fish, eggs, meat, fortified cereals (most from sunlight)

30
Q

What’s the function of Vitamin E?

Give some examples of foods

A
  • Helps protect the cells in our against damage

Veg + seed oils, spreads, nuts + seeds

31
Q

What’s the function of Vitamin K?

Give some examples of foods

A
  • Helps blood clot normally
  • Helps keep bones healthy

Green leafy veg, meat + dairy

32
Q

What are essential fatty acids (EFAs)?

A

They are fatty acids that cannot be synthesised by the body (or in adequate amounts) so is therefore essential in an individuals diet

33
Q

What are the 2 key EFAs?

Name, scientific fatty acid name, where from

A
  1. ALPHA-Linoleic acid (ALA) - 18:3n-3
  • from flaxseeds, walnuts, chia seeds + rapeseed oil
  1. Linoleic acid - 18:2n-6
  • from safflower, soybean + corn oils
34
Q

What are the requirements of % of total energy intake from these EFAs?

Is it being met?

A

Linoleic acid - >1% total EI from this

  • typically being met in the UK

Alpha Linoleic acid - >0.2% total EI from this

  • typically not being met in the UK
35
Q

What are the symptoms of a deficiency in EFAs?

A
  • Dry scaly rash
  • Decreased growth in infants + children
  • Increased susceptibility to infection
  • Poor wound healing
36
Q

List some of the key roles of EFAs

A
  1. Structural component of cell membranes
  2. Production of eicosanoids (hormone-like substances involved in innate immune response)
    - mediators in regulating biological responses (BP, vasoconstriction, immune + inflammatory responses)
  3. Converted into other longer-chain fatty acids
37
Q

What are the 2 very long-chain omega-3 fatty acids?

A

EPA - eicosapentaenoic acid

DHA - docosahexaenoic acid

38
Q

What forms EPA and DHA - what does it require, conversion rates?

A

Main sources of EPA + DHA are fatty fish (salmon + sardines) + algae oils

  • can be synthesised in body from ALA
  • requires elongase + desaturates enzymes

Conversion rate is limited!

  • 5% of ALA converted to EPA
  • Less than 0.5% converted to DHA
39
Q

What’s the recommendations of fish (also EPA + DHA recommendations)

A

2 portions of fish per week - one should be an oily fish

  • so roughly 450mg of EPA + DHA per daily adult dose
40
Q

Why is this recommendation important?

A
  • Regulates BP
  • Reduce circulating triacylglycerol levels = lower risk of premature death + lower risk of death from cancer, CVD etc
  • Improve brain function
  • Brain + eye development
  • Anti-inflammatory
41
Q

Why could traditional sources of very-long chain omega-3 polyunsaturated fats (PUFAs - EPA + DHA) be unsuitable?

A

Humans have overfished their stocks = unsustainable

  • there’s a decline in fish stocks by 24.2%
42
Q

As a result what are the suitable alternatives to marine-derived PUFAs?

A
  1. Algae oil or algae based products
  • impact on fasting triacylglycerol conc comparable to omega-3 PUFAs from fish oil
  1. Genetically modified plants (camelina sativa)
  • is as effective as fish oil for increasing EPA + DHA conc
43
Q

What’s the debate regarding saturated fat and health?

A

Whether saturated fat is bad for health or not…

  • De Souza (2015) found no association between saturated fat and health but still questioning - ‘if saturated fat is cut out, what would it be replaced with?’
44
Q

However, what did SACN (2019) report have to say about this?

A

Their evidence suggested that reducing dietary intake of saturated fat will…

  1. Reduce risk of CVD + coronary heart disease (CHD) events
  2. Lower total + LDL cholesterol levels
  3. Improve indicators of glycaemic control
45
Q

What’s the recommended daily energy intake from saturated fats?

A

No more than 10% of daily energy intake should be from saturated fats (for adults + children over 5)

  • possible to substitute saturated fats with PUFAs
  • minimal evidence to substitute with monounsaturated fats
46
Q

STUDY - isocaloric replacement of saturated fats with unsaturated fats

What does isocaloric mean + what were findings?

A

Isocaloric means the diet was the exact same in terms of calorific value, just changed in macronutrient content

  • found that replacing 5% energy from SFAs with either PUFAs or MUFAs or carbs from wholegrains = lower risk of CHD
47
Q

STUDY - randomised controlled dietary intervention + vascular function study

What was the effect of replacing 9.5-9.6% dietary SFAs with either MUFAs or n-6 PUFAs on fasting lipid profile + other CVD risk factors?

A
  1. Replacement lowered fasting serum total cholesterol + low-density lipoprotein (LDL) cholesterol
  2. The changes in LDL cholesterol conc correspond to an estimated 17-20% reduction in CVD mortality
48
Q

STUDY - what’s the difference between individual saturated fats?

Isoenergetic replacement (1% energy) from carbs with lauric acid, myristic acid, palmitic acid + stearic acid.

What was the effect of these SFAs on LDL cholesterol?

A

Lauric, myristic + palmitic acid all RAISED LDL cholesterol

Stearic acid had a NEUTRAL effect

49
Q

STUDY above - why could this be?

What’s the difference between these SFAs?

A

All are long chain fatty acids (>12 carbons)

  • but lauric, myristic and palmitic acid have 12, 14 and 16 carbons whereas stearic acid has the longest with 18 carbons
50
Q

Is coconut oil actually good for you + a ‘healthy’ alternative to other cooking oils?

A

Evidence has proven otherwise!

Coconut oils are extremely high in saturated fats (about 50% more than butter) which may be associated with an increase in total + LDL cholesterol compared to non-tropical oils

BUT there is a flipside…

  • proponents believe that some saturated fats in coconut oil (called medium-chain triglycerides) may actually raise levels of beneficial HDL cholesterol
51
Q

Why could traditional guidelines to foods now be less useful?

A

They are isolating nutrients - this was needed for certain advances in nutrition (to avoid nutrient deficiencies)

  • but may not be a suitable approach for chronic disease prevention
  • as people consume foods not individual ingredients
52
Q

What is the food matrix? - a more holistic approach

A

Whole foods consist of a variety of nutrients within a complex physical structure…
…this structure is known as the food matrix

  • it influences how nutrients are absorbed + digested

The nature of food matrix (how nutrients are organised + interact) affects the foods nutritional value + impact of health

53
Q

Why do diary products have a much more complex food matrix?

A

There’s such a difference in the type of products e.g.

Hard cheese - fermented (cultured) dairy food
- has most complex matrix
- rich in micronutrients (calcium + phosphorus) whilst also containing protein + bioactives

Butter - a water-in-oil emulsion
- contains very little calcium, phosphorus, protein + bioactives compared to hard cheese

54
Q

How does the food matrix affect the blood lipid response to saturated fatty acids from dairy?

A

Comparing matched intake of butter with hard cheese on LDL cholesterol

  • eating a higher amount of cheese compared to butter led to reduced levels of LDL cholesterol

Human Nutrition - Y2S1 (8 decks)

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