Modérateurs: Nutrimuscle-Conseils, Nutrimuscle-Diététique
par Administrateur » 21 Mai 2009 16:48
par x-men » 21 Mai 2009 16:57
par Alban » 23 Mai 2009 11:29
Method of Measuring Protein Quality
Chemical Score:The chemical score of a protein refers simply to its amino acid profile rated to some standard or reference protein, each amino acid is rated on a scale indicating how much of that amino acid is present compared to the reference protein.
For example, let’s say that the reference protein being used contains 100 milligrams of the amino acid leucine. Let’s say that the protein we’re looking at contains only 75 mg of leucine; that protein would be given a chemical score of 75% for leucine; if instead it contained 125 mg of leucine, it would be given a chemical score of 125% for that amino acid.
Frankly, chemical score isn’t used very much anymore and the whole concept is based on knowing what the ideal protein for human health and function actually is. Even in that case, chemical score says nothing about digestion or how a given protein is actually used by the body.
Biological Value(BV): BV is one of the more common methods of measuring protein quality and tends to be the one that is seen the most so I’m going to give it the most discussion. BV is simply a measure of how much of the protein actually entering the bloodstream is retained in the body (e.g. used for proteins synthesis or what have you); that is it takes digestibility into account. I’d note that some of the protein (again, researchers are actually measuring nitrogen going in vs. out but that’s not important here) that gets into the bloodstream comes back out in the urine.
Since BV is comparing protein in vs. out, the highest possible value for BV would be 100, that would mean that 100% of the protein that got into the bloodstream is being used by the body (note again, some protein won’t be digested in the first place). No protein has a BV of 100 and claims that whey have a BV of 140 are simply nonsense (they are based on a misreading of a specific paper); this would suggest that for every gram of protein from whey that is eaten, the body somehow stores 1.4 grams of protein. An impossibility.
BV is measured by feeding subjects a protein free diet for three days and then giving them a measured amount of protein, the amount that comes back out in the urine and poop and skin and such are then estimated and BV is calculated. This type of study is called a nitrogen balance study and, for a variety of reasons can be very inaccurate. Again, more detail can be found in The Protein Book.
I’d note that BV is typically tested at very low protein intakes, far below what the average American (and certainly any athlete would eat). Eating more protein lowers the apparent BV which has led to some humorously bad interpretations of BV. As well overall energy intake drastically affects BV; if you eat more calories, apparent BV goes up, if you eat less, apparent BV goes down.
Because of this, BV has a lot of practical problems. It’s very accurate under conditions of low protein intake but caloric has to be meticulously controlled. At the types of high protein intakes seen in most modern countries, as well as with athletes, BV doesn’t tend to say very much.
Net Protein Utilization (NPU): NPU is extremely similar to BV. But while BV is comparing the amount of protein that is actually digested to the amount that is stored in the body, NPU simply compares the amount of protein eaten to the amount stored in the body. Put differently, BV takes digestion and actual absorption of protein into account; NPU doesn’t. This doesn’t make NPU very useful.
Protein Efficiency Ratio (PER): PER is a measure of the amount of weight gain (in grams) in rats compared to their protein intake. It’s always measured in young growing rats and, frankly, has about zero relevance to human physiology.
Protein Digestibility Corrected Amino Acid Score (PDCAAS): The PDCAAS is the newest method of scoring protein quality and is the one most in common use. Like chemical score it compares the amino acid profile to some reference protein; as well it it takes into account digestion. Somewhat interestingly, proteins that were scored as low quality (such as soy protein) achieved a much higher score via the PDCAAS. This is actually in line with research showing that quality soy proteins work just fine for supporting basic human protein needs.
PDCAAS does have a couple of problems, however. The first is that the highest score possible is set at 1.0, no protein can score above that value regardless of the apparent quality. Basically, scores higher than 1 are simply rounded back down.
Additionally, part of the premise of the PDCAAS is that the ideal pattern of amino acids for supporting human health (or athletic performance) is actually known. It’s possible that the ideal protein for supporting basic human health might change with age (for example, amino acid and protein requirements do change with age) or might be different different types of athletes. The idea that a single amino acid profile can be ideal under all circumstances is tenuous at best.
par deric » 23 Mai 2009 18:08
par Alban » 23 Mai 2009 19:14
deric a écrit:En fait nous recherchons tous la meilleure prot avec le meilleur aminogramme possible mais notre corps ne va t'il pas digérer ces protéines les réduire en acides aminés et les recomposer selon ses besoins?
rocky a écrit:en gros sa dit quoi alban ?? parce que l'anglais et moi sa fait 4
par Persephone » 23 Mai 2009 19:21
Alban a écrit:deric a écrit:En fait nous recherchons tous la meilleure prot avec le meilleur aminogramme possible mais notre corps ne va t'il pas digérer ces protéines les réduire en acides aminés et les recomposer selon ses besoins?
Oui, c'est ce qu'il fait....
cf. à peu près les 12 articles dont je viens de donner les URLs... il y a une partie sur la digestion et 3 parties sur le profile en acides aminés.
par Donald TRex » 27 Mai 2009 20:55
Non, ce n'est pas ce qu'il fait.
Cela se comprend d'ailleurs assez facilement parce que si c'était le cas on aurait les mêmes résultats avec des protéines ayant un aminogramme identique, ce qui n'est pas du tout le cas.
Dans ce cas il suffirait aussi de prendre des protéines végétales quelconques et de compléter les AA pour avoir les mêmes effets qu'une Whey et ce n'est pas le cas non plus.
par Administrateur » 27 Mai 2009 23:26
x-men a écrit:oui tout a fait d'accord avec le chene
ah moins que la quantité d'isolat soit tres faible
Administrateur a écrit:...pour Musclewhey 3, il ne faut pas oublier de décompter l'arôme, les vitamines et les édulcorants.
par Romain » 27 Oct 2009 00:14
) ? Ou tout du moins nous confirmer celles qui ont un IC > 100 ??
par Longinus » 27 Oct 2009 11:33
