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Human Nutrition - Y2S1 > Proteins + Amino acids > Flashcards

Proteins + Amino acids Flashcards

1
Q

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

A

4kcal per 1g of protein

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2
Q

What are the main roles of proteins?

A

Provide many essential functions in body…

  1. Digestive enzymes for chemical reactions
  2. Immune functions by antibodies
  3. Regulation of expression of DNA / RNA
  4. Move blood around body (Hg)
  5. Bodily functions by hormones
  6. Contraction of muscles
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3
Q

Describe the structure of a protein

A

Amino acids bound together via peptide bonds forming a polypeptide (primary structure)

  • free amino group (N-terminus) one end
  • free carboxyl group (C-terminus) at other end
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4
Q

What are amino acids structure?

A

A central carbon bound to…

  • a hydrogen
  • a nitrogen-containing amino group (NH2)
  • a carboxylic group (COOH)
  • An R group / variable side chain
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5
Q

What are the 2 types of amino acids?

A

Indispensable (essential) amino acids

Dispensable amino acids

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6
Q

Describe indispensable amino acids and what are conditional indispensable AAs?

A

They cannot be synthesised by body so adequate dietary intake is required

  • such thing as conditional indispensable = usually not essential amino acids except in times of stress / growth / illness
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7
Q

Describe dispensable amino acids

A

These can be synthesised by the body

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8
Q

What do dietary proteins contain?

A

Usually a mix of both dispensable and indispensable amino acids

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9
Q

Describe digestion and absorption of proteins

A
  1. Mechanical breakdown in mouth (chewing)
  2. Chemical digestion in stomach - via hydrochloric acid which unfolds 3D structure revealing chain + enzymatic digestion by pepsin forming shorter polypeptides + chyme
  3. Digestion by pancreatic enzymes (trypsin, chymotrypsin + other proteases) = formation of tripeptides, dipeptides + AAs
  4. Once inside enterocytes of small intestine, all proteins are broken down to form AAs which are absorbed by blood stream + taken up by target tissues
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10
Q

What is chyme?

A

Chyme is a mixture comprised of gastric juices + partially digested food which is transported from stomach to small intestine

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11
Q

What are the dietary recommendations of protein (average weight adults - what is this for avg weighed male + female?)

A

Reference nutrient intake (RNI) for average-weight adults is 0.75g protein / kg of body weight per day

  • Females - 45g / day (60kg)
  • Males - 56g per day (75kg)
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12
Q

Why would males required more typically + how does protein need change for active individuals?

A

The greater protein intake for males is required to maintain nitrogen balance for muscle mass

  • highly active individuals + growing children + pregnant women require more protein
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13
Q

How is protein intake different between continents?

A

India + Asia - meeting protein recommendation for an individual weighing 62kg (a lot from plant-based protein)

EU + US - these protein recommendations are sig. exceeded (a lot from animal protein)

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14
Q

What are the 2 kinds of severe acute malnutrition (affected by protein intake)

A
  1. Kwashiorkor
  2. Marasmus
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15
Q

Describe Kwashiorkor in more detail

Cause, age group, subcutaneous fat, oedema, liver, muscle wasting

A

Cause - protein deficiency
Age group - 6mo -> 3yrs
Subcutaneous fat - preserved
Oedema - present (build-up of fluid in body)
Liver - enlarged fatty liver
Muscle wasting - mild or absent

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16
Q

Describe Marasmus in more detail

Cause, age group, subcutaneous fat, oedema, liver, muscle wasting

A

Cause - protein + energy deficiency
Age group - < 1 yr
Subcutaneous fat - not preserved
Oedema - absent
Liver - no fatty liver
Muscle wasting - severe

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17
Q

How is excess protein stored?

A

It is stored as fat or excreted in urine

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18
Q

Why is excess protein a bad thing?

A

Metabolic burden

  • Bones = high protein intake increases calcium excretion = bad bone health
  • Kidneys = strain from filtering excess nitrogen
  • Liver = overburdened metabolism

Increased disease risk

  • heart disease + cancers - high animal proteins (red / processed) = coronary heart disease + some cancers
19
Q

What could also be an underlying reason for increased disease risk from excess protein intake?

A

Often due to excess animal protein (red / processed) which often contain high amounts of saturated fats

20
Q

How are proteins ranked + what is it dependent on?

A

Based on quality - how many AAs are present in biologically available format (20 key amino acids)

  • dependent upon proportion of protein-derived AAs from digestion
  • how similar are the AAs to those found in human cells
21
Q

What is the protein quality score based on?

A

Amino acid composition, digestibility of essential AAs, human requirement of essential AAs

  • PDCAAS - quality based on faecal digestibility
  • now replaced by DIAAS - based on ileal digestibility
22
Q

What are the 2 types of proteins based on quality?

A
  1. Complete proteins (high quality) - provide adequate amounts of all 9 essential AAs (e.g. animal proteins, soy, mycoprotein)
  2. Incomplete proteins (low quality) - do not contain adequate amounts of >1 essential AAs (e.g. nuts, grains, seeds, legumes)
23
Q

So should you only eat complete proteins?

A

NO, obviously not!

It is possible to combine incomplete proteins sources to provide all 9 essential AAs

e.g. peanut butter on toast - complementing legumes (PB) with grains (bread) = complete protein

  • however protein complementation does not need to be done at same meal to meet protein needs
24
Q

Where is the largest reservoir for body protein?

A

Skeletal muscle - accounts for roughly 50% of total body protein

25
Q

Muscle protein metabolism in young adults

What are the 2 key processes?

A

Muscle protein turnover (replacing older protein)

  1. MPS - muscle protein synthesis = building new protein
  2. MPB - muscle protein breakdown = degradation of muscle protein
26
Q

What stimulates MPS?

A

Protein ingestion (food intake) and resistance exercise

27
Q

What happens as you get older in relation to muscle protein?

A

Sarcopenia

This is the biological ageing process associated with a gradual loss of skeletal muscle mass + function leading to…

  • Reduced mobility = loss of independence
  • Frailty
  • Impaired metabolic adaptation to illness + disease
  • increased mortality
28
Q

What else occurs as you get older?

A

Anabolic resistance

29
Q

What is anabolic resistance?

A

The reduced ability of muscle tissue to synthesise protein in response to anabolic stimuli (food intake + PA)

  • blunted MPS response (as reduced sensitivity to stimuli)
  • increased MPB risk (if outpaces MPS = muscle loss / sarcopenia)
30
Q

As a result, the issues in older adults regarding protein breakdown means…

A

They need to intake more protein

  • More dairy products (milk, cheese, yoghurts)

This helps to maintain muscle mass + micronutrients (calcium, potassium) for normal muscle function

  • research has shown hand-grip strength went up after 12 weeks period of incorporating ricotta cheese into diet
31
Q

Therefore, the recommendations for older adults is…

A

At least 1-1.2g of protein / kg per day

  • upwards of 1.5g may be needed for adults with acute / chronic illnesses
  • also with PA for as long as possible

Nutrition in combination with exercise is optimal for muscle function

32
Q

What are the pros of animal derived protein sources?

A

+ High quality dietary protein with essential amino acids for muscle protein synthesis
+ highly digestible
+ Contributes to micronutrient intake

33
Q

What are the cons of animal derived protein sources?

A
  • Red + processed meat = risk of colorectal cancer
  • Animal production linked to greenhouse gas production + nitrogen pollution
  • Puts unsustainable pressure on land, water + global resources
34
Q

What is the worst animal protein for greenhouse gas production?

how does it compare to plant-based proteins?

A

Beef produces largest levels during production - 50kg CO2eq per 100g protein) with next highest level being lamb at 20

  • beans, nuts, tofu are <2
35
Q

What do eat-lancet recommend humans should do?

A

We should adopt a ‘planetary healthy diet’ whereby minimal greenhouse gases are produced

  • however can this feed a population of 10 billion people? - big Q’s
36
Q

How could environmental impact of protein production be reduced?

A

Consume more alternative sources of protein which offer a more sustainable source for human food (+ animal feed)

  • this will reduce excessive intake of animal proteins

BUT it needs to be safe, affordable + acceptable for consumer (in terms of taste + texture etc)

37
Q

What are these alternative options to animal protein?

A
  1. meat analogues with plant proteins - look + taste like meat
  2. growing meat in lab with stem cells from animals
  3. fermentation derived protein (mycoprotein)
  4. edible insects - 4 species already accepted in europe
  5. algae - seaweed (macro) + microalgae
38
Q

What is mycoprotein?

A

A whole food produced by the continuous cultivation of filamentous fungus ‘Fusarium venenatum’

39
Q

Why is mycoprotein a good alternative to animal protein?

A

It is a complete protein source!

  • also the biomass fermentation uses the rapid growth of some protein-rich microorganisms to make large amounts of protein
40
Q

What are the potential advantages of plant-based diet?

A

+ lower GHG emissions
+ lower T2D risk
+ dietary fibre + lower saturated fats
+ lower CVD risk
+ phytochemicals + antioxidants (strengthen immune system, reduce inflammation etc)
+ just as good at improving muscle strength

41
Q

However is there downsides to these plant-based diets?

A
  • lower digestibility
  • lower protein content per serving
  • lower essential AA content
42
Q

How can the disadvantages of plant-proteins be overcome?

A

Lower digestibility - soaking, germination, cooking, industrial processing + use of probiotics / digestive enzymes
-protein isolate / concentrate
Protein content - increase portion size
- combine food groups
Lower EAA - fortification of protein supplements with specific AAs

43
Q

What is a blended protein approach?

A

Done by consumers of animal-based proteins who want to consume a more sustainable diet

e.g. combining pea protein with whey protein in shakes

Human Nutrition - Y2S1 (8 decks)

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