Proteins + Amino acids Flashcards
What’s the energy source from proteins? (kcal)
4kcal per 1g of protein
What are the main roles of proteins?
Provide many essential functions in body…
- Digestive enzymes for chemical reactions
- Immune functions by antibodies
- Regulation of expression of DNA / RNA
- Move blood around body (Hg)
- Bodily functions by hormones
- Contraction of muscles
Describe the structure of a protein
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
What are amino acids structure?
A central carbon bound to…
- a hydrogen
- a nitrogen-containing amino group (NH2)
- a carboxylic group (COOH)
- An R group / variable side chain
What are the 2 types of amino acids?
Indispensable (essential) amino acids
Dispensable amino acids
Describe indispensable amino acids and what are conditional indispensable AAs?
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
Describe dispensable amino acids
These can be synthesised by the body
What do dietary proteins contain?
Usually a mix of both dispensable and indispensable amino acids
Describe digestion and absorption of proteins
- Mechanical breakdown in mouth (chewing)
- Chemical digestion in stomach - via hydrochloric acid which unfolds 3D structure revealing chain + enzymatic digestion by pepsin forming shorter polypeptides + chyme
- Digestion by pancreatic enzymes (trypsin, chymotrypsin + other proteases) = formation of tripeptides, dipeptides + AAs
- 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
What is chyme?
Chyme is a mixture comprised of gastric juices + partially digested food which is transported from stomach to small intestine
What are the dietary recommendations of protein (average weight adults - what is this for avg weighed male + female?)
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)
Why would males required more typically + how does protein need change for active individuals?
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
How is protein intake different between continents?
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)
What are the 2 kinds of severe acute malnutrition (affected by protein intake)
- Kwashiorkor
- Marasmus
Describe Kwashiorkor in more detail
Cause, age group, subcutaneous fat, oedema, liver, muscle wasting
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
Describe Marasmus in more detail
Cause, age group, subcutaneous fat, oedema, liver, muscle wasting
Cause - protein + energy deficiency
Age group - < 1 yr
Subcutaneous fat - not preserved
Oedema - absent
Liver - no fatty liver
Muscle wasting - severe
How is excess protein stored?
It is stored as fat or excreted in urine
Why is excess protein a bad thing?
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
What could also be an underlying reason for increased disease risk from excess protein intake?
Often due to excess animal protein (red / processed) which often contain high amounts of saturated fats
How are proteins ranked + what is it dependent on?
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
What is the protein quality score based on?
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
What are the 2 types of proteins based on quality?
- Complete proteins (high quality) - provide adequate amounts of all 9 essential AAs (e.g. animal proteins, soy, mycoprotein)
- Incomplete proteins (low quality) - do not contain adequate amounts of >1 essential AAs (e.g. nuts, grains, seeds, legumes)
So should you only eat complete proteins?
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
Where is the largest reservoir for body protein?
Skeletal muscle - accounts for roughly 50% of total body protein
Muscle protein metabolism in young adults
What are the 2 key processes?
Muscle protein turnover (replacing older protein)
- MPS - muscle protein synthesis = building new protein
- MPB - muscle protein breakdown = degradation of muscle protein
What stimulates MPS?
Protein ingestion (food intake) and resistance exercise
What happens as you get older in relation to muscle protein?
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
What else occurs as you get older?
Anabolic resistance
What is anabolic resistance?
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)
As a result, the issues in older adults regarding protein breakdown means…
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
Therefore, the recommendations for older adults is…
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
What are the pros of animal derived protein sources?
+ High quality dietary protein with essential amino acids for muscle protein synthesis
+ highly digestible
+ Contributes to micronutrient intake
What are the cons of animal derived protein sources?
- Red + processed meat = risk of colorectal cancer
- Animal production linked to greenhouse gas production + nitrogen pollution
- Puts unsustainable pressure on land, water + global resources
What is the worst animal protein for greenhouse gas production?
how does it compare to plant-based proteins?
Beef produces largest levels during production - 50kg CO2eq per 100g protein) with next highest level being lamb at 20
- beans, nuts, tofu are <2
What do eat-lancet recommend humans should do?
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
How could environmental impact of protein production be reduced?
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)
What are these alternative options to animal protein?
- meat analogues with plant proteins - look + taste like meat
- growing meat in lab with stem cells from animals
- fermentation derived protein (mycoprotein)
- edible insects - 4 species already accepted in europe
- algae - seaweed (macro) + microalgae
What is mycoprotein?
A whole food produced by the continuous cultivation of filamentous fungus ‘Fusarium venenatum’
Why is mycoprotein a good alternative to animal protein?
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
What are the potential advantages of plant-based diet?
+ 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
However is there downsides to these plant-based diets?
- lower digestibility
- lower protein content per serving
- lower essential AA content
How can the disadvantages of plant-proteins be overcome?
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
What is a blended protein approach?
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
