What are proteins
Chains of amino acids
Protein classification
- Polypeptide
- Chains of AAs linked by a peptide bond
- Dipeptide
- Simplest polypeptide
- Tripeptide
- Oligopeptide
Explain essential and non-essential protein
Essential - the body cannot synthesis (diet)
Non-essential - body can synthesis
Function of protein
- Synthesis of body protein
- Structural parts of all cells
- Muscle, skin, hair
- Bones and teeth (minerals embedded in protein structure)
+ Deficiency in protein - these structure break down:
^ Reduced muscle mass, loss of skin elasticity, thinning of hair
Protein for fuel at rest and exercise
- Estimated contribution of protein to energy expenditure at rest 5 - 15%
- During exercise ↑ carbohydrate and fat oxidation
- Contribution of protein to oxidative metabolism in prolonged exercise < 5%
Protein turn over and net protein balance
proteins are continually breaking down and synthesizing
Net balance
The area of protein synthesis - the area of protein breakdown = protein gain or loss
Amino Acid pool
Small pool of amino acids
- 120g of free amino acids are present in the skeletal muscle of an adult
- Amino acids are constantly extracted from the free amino acid pool for synthesis of various proteins, and breakdown of protein makes amino acids available for the free amino acid pool
Protein breakdown
- Purpose
Serves 3 main purposes:
- Degrades potentially damaged proteins to prevent a decline in their function
- Provides energy when some individual AAs are converted to Acetyl CoA – oxidized in the mitochondria
- Synthesis of other compounds
Protein -> breakdown -> amino acid -> amino acid -> new protein
What is transamination
Before proteins can be oxidised:
- Amino group must be removed
- This is achieved by transferring it to another molecule called a keto acid
- Resulting in the production of another type of AA
- This process is catalyzed by aminotransferase
What is Deamination
Before proteins can be oxidised:
- Amino group must be removed
* Amino group can be removed to form AMMONIA
* Ammonia is toxic and is either:
+ Used to form glutamine from glutamate or alanine from pyruvate within the muscle
+ Transported to the liver; converted to urea and excreted
What happens after the removal of the amino group
- The remaining carbon skeleton (the keto acid) is eventually oxidised to CO2 in the TCA cycle
How does it enter the TCA:
- Acetyl-CoA
- Alpha ketoglutarate or oxaloacetate – metabolites of glutamate and aspartate respectively
Amino acids to protein
- Regulatory
- Structural
Regulatory (e.g. enzymes)
- Mins, hrs, days
Structural (e.g. collagen and contractile protein)
- Days, weeks, month
Protein quality
- complete/non complete
Complete
- Not deficient
Incomplete
- Deficient in one of more amino acids
Quality of protein
1 (highest) - after digestion of the protein it provides 100% of essential amino acid required
0 (lowest)
Example of high quality
- Whey protein
- Egg white protein
- Casein protein
- Milk protein
- Soy protein
We generally refer to the QUALITY of protein as its ability to support the increase of muscle protein synthesis after ingestion.
- Stimulate muscle protein synthesis
- Protein digestive capacity
- Amino acid absorption efficiency
- Essential amino acid - leucine
- Protein turn over at rest
- Protein turnover and diet
- Protein turnover and resistance training
- Protein intake and protein synthesis
- Factors affecting protein synthesis
Rest
Negative protein balance
Diet
- Meal to meal fluctuations in muscle protein synthesis influence gains and losses in skeletal muscle mass
- Possible to increase net protein synthesis at rest with regular meals containing 10- 20g of protein.
Resistance training
- Resistance exercise (of sufficient intensity) stimulates mixed muscle protein synthesis and breakdown
- Protein synthesis is stimulated more than breakdown
- Net muscle protein balance is improved
- EXERCISE improves muscle protein synthesis (MPS) but… NOT enough to enter a NET POSITIVE MPS state
- RT volume: best - Unilateral 8 x 10 @ 80% 1RM
Protein intake and protein synthesis
- Hours after exercise - Protein synthesis may exceed protein BREAKDOWN BUT… Only after AA feeding
- Strongest stimulus = training + protein intake
Factors affecting protein synthesis
- Co-ingesting of other nutrients
- Amount of protein
- Timing of intake
- Type of protein
Co-ingestion of other nutrients
- CHO
- Milk
CHO
- CHO alone doesn’t stimulate protein synthesis
- CHO combined with protein had the greatest effect net protein balance
- Increase in insulin levels
- Reduction of protein breakdown (from CHO)
- Small increase in protein synthesis
Fat free milk vs Whole fat milk
- Fat free milk delayed the delivery of amino acids
- Whole milk is best
Amount of protein
Recommended intake
- General populations: 0.8g/kg
Athletic populations
- Strength athletes: 1.5 - 1.7g/kg
- Endurance athletes: 1.2 - 1.6g/kg
- Timing of intake
- strategies of consumption
There was a common belief that there was an narrow anabolic window (for building muscle). However, through evidence this window was shown to be larger
- 3hr is best but still have a 48hr winder
Strategies
- Bolus: 2 meal with 40g of protein over 12hrs
- Intermediate: 4 meals of 20g of protein over 12hrs (produces best results)
- Pulse: 8 meals of 10g of protein over 12hrs
Type of protein
Digestive properties of proteins influence the anabolic response at rest and exercise
- SLOW: takes the body longer to breakdown and absorb
- FAST: body digests and absorbs rapidly
Milk
- Whey (20%) - fast
- Casein (80%) - slow
Soy protein
- fast
Milk vs soy protein
- Milk based has a larger protein synthesis rate
Whey vs Casein - Whole body protein synthesis is stimulated with whey and supressed with casein
Whey vs Casein vs soy
- Muscle protein synthesis the greatest following whey. Soy higher then casein
Leucine
Stimulates the mTOR, a key signalling protein and triggers a rise in muscle protein synthesis
Protein high in LEUCINE is beneficial
- Whey: 10g per 100g
- Casein: 8.2g per 100g
- Soy: 5.9g per 100g
- Leucine threshold that stimulates muscle protein synthesis appears to be about 3g leucine per meal.
- Consideration in determining protein recommendations
- 0.4 g.kg.meal (4 meals)
Training stimulus TYPE
Metabolic response of individual proteins may respond differently to training stimulus
- Different training different amount of protein synthesis in a different area
Different areas for protein synthesis
- Myofibrillar proteins
- Mitochondrial proteins
- Sarcoplasmic proteins
Resistance training
- Higher myofibrillar protein synthesis rate
Endurance training
- Higher mitochondrial protein synthesis rate
Supplementing with BCAAs
- Types of BCAA
- BCAA claims
- Glutamine
BCAAs
- Leucine, Isoleucine, Valine
- Not synthesized in the body (essential AAs)
- Oxidised during exercise
- Must be replenished in the diet
BCAA
- Fuels during exercise and spare glycogen
- Increase protein synthesis following exercise.
- Reduce net protein breakdown in muscle during exercise.
- Reduce muscle damage and soreness
Reduce fatigue.
Glutamine
Non-essential AA
- Many very important roles:
* Nitrogen transport
* Acid-base regulator
*Used by white blood cells
Normal intake: ~3 to 6 g/day Supplement claims for Glutamine:
- Fluid absorption
- Muscle protein balance
- Muscle glycogen synthesis
- Muscle damage and soreness
- Immune system
