Protein Nutrition Question PDF

Preview

Summary

Protein example essay answer...

Description

Describe the metabolic fate of dietary protein and discuss the potential implications this may have in terms of both physical performance and the adaptations to various types of exercise. Protein metabolism denotes the various biochemical processes for the synthesis of proteins and amino acids (Anabolism) and the breakdown of proteins (catabolism). 

The component parts of protein (amino acids) enter the body’s free amino acid pool (body fluids and tissues) from the protein foods we ingest, from the breakdown of body protein, and/or dispensable (nonessential) amino acids, synthesised from CHO or fat and ammonia.  In non-growing human an equilibrium exists such that the body protein that is continually being broken down is replaced by protein synthesised from amino acids in the free pool.  However, if dietary protein is less than adequate there are insufficient amino acids entering the free pool to maintain a rate of protein synthesis to counteract protein degradation, ultimately known as catabolism.  In contrast when protein intake is excessive the surplus amino acid carbon is oxidised and/or converted into CHO or fat and stored while the surplus nitrogen is largely excreted (primarily as urea in urine)  Proteins are made up of chains of amino acids, which contain an amine group (NH3+), carboxyl group, side chain variable R group and an alpha carbon.  When ingesting dietary protein the overall fate of these molecules is that a small amount of protein is synthesised maxing out at around 1.4-1.7g.kg.bm.day which has a high energy requirement (20% of total energy intake), some of the protein is oxidised and a lot of protein is excreted due to the attached amine group (nitrogen) being toxic Protein metabolism details (1) Inter conversion of Amino Acids  Appearance of Amino acids in the blood that you already have a lot of these will undergo the process of transamination This is the conversion one AA to another so  One AA, then in a Schiff base rearrangement take N away  known as deamination and give to another Carbon skeleton and leave the one you don’t want which can then go on to be used in CHO or lipid metabolism. Having removed nitrogen from deamination you can then go onto: 1) Use deaminated carbon for energy  Carbon skeletons go into CHO or lipid metabolism (glycogenic undergo gluconeogenesis, ketogenic (Acetyl CoA for TCA cycle or ketone bodies brain alternative energy source or mixed) 2) New amino acid for anabolism (transamination)  Excess must be excreted i. Transamination often used to produce alanine which safely transports excess nitrogen to the liver ii. Arrives at liver; transaminase operates on alanine producing 1. glutamate/ aspartate produced which can go one of 2 ways 2. Oxaloacetate/ alpha ketoglutarate 3. NH4+ Transaminase of alanine produces glucose for liver glycogen storage or hepatic glucose output Muscle liver cycle: - Muscle uses transamination to get the amino acids it wants often producing alanine - Liver uses this to create glucose which is then provided back to the muscle Hepatic Urea formation: - Ammonia must be excreted - This prevents toxicity and makes the nitrogen soluble and easy to excrete in urine (but costs energy!!) 1) Ammonium  carbamoyl phosphate (involving bicarbonate) uses 2 ATP 2) Carbamoyl phosphate feeds into urea cycle, uses aspartate which liberates fumarate which passes onto TCA cycle which provides aspartate (In a cyclic fashion, anaplerosis) 3) Urea can now safely be transported into blood and be filtered into urine by kidneys (major method of N+ excretion with 90% of protein excretion done this way but there is an alternative Remaining 5-10%:  Converted into their neutral amides rather than entering urea cycle  Glutamate and aspartate into glutamine and asparagine (pick up H+)  Glutamine and asparagine are carried to the kidneys where amonia diffuses into filtrate  Go back to glutamate and aspartate which are then excreted into urine

And so, when there is insufficient protein this undergoes catabolism and results in subsequent degradation of protein such as muscle protein, however when protein intake is in excess of demands the majority of it is excreted as amino acids cannot be stored due to toxicity which takes up approximately 1/3 of our daily energy intake and so protein balance is an essential part of dietary protein intake. There is an understanding that:  Resistance training increases myofibrillar protein components you have (actin, myosin etc)  And endurance exercise results in production of proteins such as mitochondria and tissue turn over (catabolism of tissue to make way for better adapted tissue)  Both resistance and prolonged dynamic exercise induce catabolism in post exercise period so if protein intake isn’t high enough to suit demands after exercise athletes will be in a net state of catabolism losing protein faster than you are making it and so the idea is that.. 

Supplements may provide a more anabolic cellular environment by having more Amino acids o Which can facilitate the accretion of muscle protein as athletes want to be in a net anabolic state then perhaps they have a higher need for protein?



Tarnopolsky et al (1988) used sedentary controls vs athletes using a nitrogen balance method o PPTs ingested either low protein 1-1.7g.kg.day or high protein 1.9-2.7g.kg.day over 10 days o Energy balance reached for controls at 0.8.g.kg.day of protein which is the guided RDA (Tarnpolosky review, 1990; American Medical Association). This is the ideal as you cannot store amino acids and so nitrogen balance is essential as exposure to too high amount of protein can result in damage to organs such as the kidneys.



So… athletes do require more protein, but this is a very minor shift, perhaps noise in the measurement method differences between resistance trained and endurance trained athletes. o Resistance exercise requires more protein, but intake is still needed to maintain CHO and Protein

Amount  Large feedings of protein can often make you feel nauseous, and fuller for longer due to slow gastric emptying, foaming and so often CHO are reduced.  And if there are increases of dietary protein as an expense of CHO intake, this can reduce net protein gain via reduced training (glycogen loading ability and quality) or cataplerosis (not producing anabolic by-products of protein metabolism for synthesis instead just for CHO/lipid metabolism). o The urea cycle can deplete the intermediates of the TCA cycle, one is in a higher rare of flux and depletion in TCA cycle perhaps influences fatigue (Billsbrough and Mann, 2006).  Can perhaps be worried about ingesting not enough but the result of consistently overloading the system with protein should not be underestimated. o Over ingestion of protein also referred to as “rabit starvation syndrome” symptoms of diarrhea, nausea and death within 2-3 weeks, explained by the inability of the liver to sufficiently upregulate ureagenesis to cope with large loads of protein (Leib, 1929).  Houltham and Rowlands (2014) studies female endurance athletes. o Whilst the average protein requirements were what would be expected around 1.2g.kg.h, there is a very big range within athletes (1.2-3.8g.kg.h) which should be considered. o However, many of these endurance athletes had a high training volume but low CHO intake and so a lot of protein was being used for the conversion of glycogenic amino acids to glycogen glycogenic amino acids being converted to CHO.  Nutrition diet + nutrition survey (2013) those who take part in more activity, more protein is ingested that in the general population diet (1.6g.kg.day). o However, most people intake more protein than that is required without the additional support of a supplement. Additionally, athletes tend to take protein supplements in bolus amounts and so how much dosage is needed for a oneoff drink to aid training adaptation? Not total protein but after work out want enough to give signal. Dosage of one-off drink! 

Moore et al (2009) used egg protein for simple leg extensions. Participants ingested 5, 10, 20 and 40g in bolus amounts after a work out to give the signal for synthesis of proteins.

Significant difference in 5-20g, 40g was higher but not significantly so, worth discussing smallest worthwhile effects o a further study by McNaughton et al (2016) (n=6) where participants were ingesting whey protein, found a significant difference between 20 and 40 g of protein.  Perhaps due to different protocols using whole body resistance exercise compared to simple leg extensions and so protein is shared between each muscle group. Also, perhaps whey protein was more effective than egg protein and in terms of protein synthesis 40g is as effective as 20g but just detectable in McNaughton study. Influence of number of participants. Moore et al (2009) intake of only 20g of intact protein maximally stimulates protein synthesis over 4 hours post exercise. o Muscle protein synthesis and leucine oxidation rate (marker of catabolic response) shows intake of only ~20 g intact protein maximally stimulates protein synthesis over 4 h post exercise. o For adaptation the excess is simply oxidised due to high Michaelis Constant (Km) of catabolic enzymes (plus tachyphylaxis?) the muscle is fully saturated with protein and so the muscle shows full effect. o Even infusion studies have shown infusion of AAs have shown muscle is full and will not utilise AAs. o Feed amount of protein that gets synthesis as high as possible without increasing catabolic enzymes. 40 certainly increases leucine, so perhaps 20 is better. (Moore et al, 2015) Age effect linked to dose required, younger people required less protein (20g). o Older people require a bigger signal to onset accretion of muscle so need a bigger dose to stimulate the response. Energy intake considering amount. o More than 1/3 of your daily required energy is used for protein synthesis (20%) and the other 10% is required for gluconeogenesis and ureagenesis (Rolfe & Brown, 1997). o Protein metabolism is expensive: making proteins costs 10 x more than signal, mRNA response costs a lot less energy so can show bigger responses). Calloway and Spencer (1954) Varying levels of caloric intake, vast differences in protein intake. o Ingesting Sub optimal amount of calories but ingesting vast quantities of protein with sub optimal calories. Only when you hit energy balance that you can hit nitrogen balance! o Cannot be in a catabolic and anabolic state at the same time (building phase gaining muscle, cutting phase losing fat). Time is the key word, dependent on time period large time period it can be. Longland et al (2016) for 28 days used a 40% energy deficit (Large deficit) plus resistance exercise with either normal (1.2g.kg.day) or high (2.4.g.kg.day protein), showed a reduction in BM, greater reduction in fat mass but increases in lean body mass. o Taking precise (Dexa, bioelectrical impedence and x-ray) and extreme measures you can detect in theory that you can be catabolic and anabolic at the same time in the time frame of 28 days. But in a net period to gain tissue and lose fat tissue need to be done over a prolonged periods. o











Summary amount: Even just a small amount of protein will help to maximise protein synthesis want at least 25g of protein per meal per day (gets the maximum in a bolus amount), any excess protein can cause GI discomfort also makes you feel full so may not take on as much CHO Time 

  

Tipton et al (2009) Intense leg resistance exercise routine and During recovery ppts ingested either H2O (placebo) or 40g essential amino acid solution (taste gross) 1-2 hours during and after exercise. o Showed increased protein synthesis (increased PHE by 20-30 units). o Increased protein synthesis and similar magnitude of breakdown in the muscle. If you Stay fasted after exercise you remain in net catabolic state which is not what athletes do not want to do Ingestion of protein (amino acids) over several hours you see accretion of lean tissue (from negative to positive protein) However, decreased break down may not be a good thing  to adapt doesn’t just add tissue, it recognises sub optimal tissue and breaks it down to get rid of sub optimal tissues for better adapted ones.



During exercise you increase blood flow to musculature by default delivering AA at the time. Uptake of PHE (amino acid common in muscle) closely mirrored this in this study; suggests why whey protein may be better than essential AA’s (EAA’s taste gross, Whey partically hydrolysed but can get a large amount in the body)

Tipton et al (2001)  Intense leg resistance exercise ppts ingested either CHO + AA or just AA pre- exercise or post exercise  Post exercise uptake of Amino acids (PHE) is much lower compared to pre exercise o CHO + AA uptake are encouraged by insulin. o CHO encourages uptake of AA in general  But Ingesting protein pre-ex gives a far better protein synthesis rate, attributed to PHE  PHE uptake greater in 3 hours recovery when Protein had added CHO  Idea that pre-is advantageous over post because of blood flow  Raise AA in blood before exercise (hyper aminoacidemia)  Then you during exrcise increase blood flow to musculature by default delivering AA at the time, uptake of PHE closely mirrored this suggests why protein may have been better pre Pihoker et al (2018)  Female endurance athletes consumed CHOPRO supplement pre, post or control (no protein) high intensity resistance training o pre no better than post in practise CHO-PRO mixture pre or post or control o CHO protein mixture pre and post was better than control  The present study demonstrates that neither pre- or post-workout protein-carbohydrate supplementation is superior in stimulating body composition or lower body strength adaptations but may be more effective for upper body strength  the anabolic window for nutrient timing is likely not limited to PRE or POST, but the two interact. Tipton et al (2007)  Follow up study, intense leg resistance exercise pre or post exercise ingested o intact protein (needs to be digested first and blood flow doesn’t benefit like infusion)  Pre-exercise helps delivery the protein but to get the benefits protein needs to be hydrolysed into its respective AAs.  Post No difference, uptake is lower in both  After 4 hours both uptake pre and post is the same  It is generally advised to ingest 20-25g of high quality dietary protein immediately after the cessation of exercise as a means to optimise post exercise reconditioning if you have a short recovery time for better adaptation  Protein may even be ingested before and or during exercise to stimulate post exercise muscle protein accretion further and prevent post exercise catabolic state  Protein ingestion following exercise increases muscle protein synthesis rates, stimulates net muscle protein accretion and facilitates the skeletal muscle adaptive response to prolonged exercise training - Recent studies show protein ingestion before and during exercise also increases muscle protein synthesis rates during resistance and endurance exercise - Nutrition is requited to allow proper muscle reconditioning and is a pre- requisite for muscle hypertrophy to occur - When protein is ingested following a single bout of exercise, muscle protein synthesis rates are increased to a much higher level and for a more prolonged period of time than in normal postprandial muscle protein synthetic response - Protein supplementation represents an effective strategy to augment further skeletal muscle adaptive response to more prolonged resistance exercise training resulting in greater gains in skeletal muscle mass Type Essential Amino Acids may be best but taste vile… (Tipton, 2001) Phillips (2002)  Study from 6 labs, (8-16 weeks of resistance training) 241 men (excluded creatine) of CHO/placebo, whey protein and soy protein  Gain of around 2 kg of lean tissue gain with less than half of that with placebo or just CHO  Ingestion of any protein can be helpful  3 x the amount of muscle gain when having protein around resistance training than not Mitchel el al (2015)  Milk protein Vs Whey protein consumption in middle aged men on muscle protein synthesis  Milk has the capacity to aid protein ingestion as they found similar levels of protein synthesis to whey  animal proteins more beneficial as synthesising the right AAs

 

Milk with fat was better Suggestion: start with milk as a base for athletes and spike with leucine/ whey for maximum levels of protein synthesis Schroeder (2013) Input of Anabolic hormones post resistance exercise (testosterone, Growth hormone and IGF-1): 3 things must be there for growth to occur: 1) When ingesting AA provides building blocks to make proteins (What you want to make) 2) Get the signal, flicks a switch in the muscle to synthesise tissue 3) Tissue needs to give you energy for the expensive process (costs about 1 calorie to burn every gram of protein)  Need physical building blocks of proteins, the growth signal plus energy to turn the signal on So are acute exposures anabolic hormones needed after resistance exercise to promote protein synthesis?  Whilst training to get a hormone response may not be necessary, we can use this understanding that if we get a total elevation of testosterone over 24 hours, that might be more helpful than an accumulated exposure than short spikes of training. Men get non-stop testosterone (Phillips) Aceiro (2013): Linked with time  Typical daily intake: 3 meals per day in this study high protein 3 time per day or high protein over 6 meals  Increased protein and increased frequency decreases body mass, increases lean body mass and favourably affects cytokines  By reducing time in a day spent in a catabolic state  So what you want is a big enough bolus of best type of AAs for protein synthesis and space out these evenly Tipton et al  Ingestion of a mixture of 6g Essential AAs + 35g sucrose before exercise was more effective for the stimulation of post exercise muscle protein synthesis  May be attributed to combination of increased AA levels at a time when blood flow is increased during exercise thereby offering a greater stimulation of muscle protein synthesis by increasing AA delivery to the muscle  Dietary protein ingestion before and or during exercise may provide a more effective feeding strategy to improve AA availability during early post exercise recovery  The observation that muscle protein synthesis rates can be elevated during exercise could be of particular relevance as it may extend the window of opportunity during which muscle protein synthetic response to exercise can be facilitated  Window of opportunity: Muscle protein synthesis is already stimulated during exercise when protein is provided before or during exercise, the latter may extend the window of opportunity and accelerate skeletal muscle reconditioning  So it may be particularly wise to ingest protein before and during more prolonged endurance events as this may prevent excess muscle protein breakdown and allow muscle protein synthesis to be elevated throughout the exercise sessions  Overnight recovery of sleep  muscle protein resynthesis is low  Dietary protein ingestion after exercise increases post exercise muscle protein synthesis rates stimulate net protein accretion and facilitates the skeletal muscle adaptive response to prolonged exercise training  Protein ingestion before and/or during exercise may inhibit muscle protein breakdown stimulate muscle protein synthesis and further augment skeletal muscle adaptive response to exercise  Tipton (2000) protein and AAs for athletes: an acute bout of exercise has a dramatic effect in the rate of muscle protein synthesis  As long as energy balance is achieved and food of a normal protein content (12-15% total energy) is consumed even athletes in training should not require additional protein supplements in their diet Protein synthesis:  6g of essential amino acids can stimulate muscle protein synthesis potentially most effective pre-exercise (Tipton, 2001)  However, doubli...