On September 5, 2011, in General Nutrition, Protein, Tests, by Andrea

I’ve been slow on my ASMBS posts. I know it, but life has a funny way of getting in the way..

A discussion of late on the BBGC is about collagen protein supplements, and of course how they are either good or bad for supplementation. So it’s spurring me to share one of the things I learned while down in Orlando: how to figure PDCAAS.

There are calculators out there, or you can usually hit me up and beg for a score as I’m generally curious as well. And in the past, I’ve used the calculators because I never knew how to do this myself.. but now I do and it’s interesting how it’s done.

In the future will I continue to use the calculators? Possibly. We’ll see. I’m kinda old fashioned in a number of ways, and I may choose to keep doing the long-hand method just to keep up the practice (and to impress everyone..) but at least now I’ll have the choice.

And so will you.

First off, a quick protein primer.

Body proteins, including muscle, are made of 20 amino acids. Of these 20 amino acids, 9 must be consumed via food or modular protein supplements of some sort. These 9 are called Indispensible Amino Acids. The other 11 can either be consumed or created by the body, given that there are enough IAAs and nitrogen to create them. The 9 IAAs are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. In order for a protein to be complete and able to be truly bioavailable by the body, a protein food or supplement must have these nine IAAs.

Here’s a slight exception to the rule (don’t you love these?): the body does keep a slight pool of histidine in reserve — in normal people with normal guts, with normal digestibility, with normal food tolerances, and no other issues. Do bariatric patients keep histidine in reserve? Possibly – especially those of us further out and more normal than most. But I would not count on it. But how does this affect all of this? When I get down to the math below, if histidine is the limiting amino acid, it is possible that the protein product is okay, even thought the PDCAAS says it’s crap simply due to this “pool” — but I generally like to play it safe when it comes to saving things like heart muscle…

PDCAAS, or the protein digestibility corrected amino acid score, is a protein evaluation method proposed back in 1991 to replace some of the other methods of evaluating protein sources such as BV (biological value), NPU (net protein use), and PER (protein efficiency ratio). The main difference between PDCAAS and its predecessors is that it evaluates protein adequacy based on the limiting amino acid found in the protein. Basically, it ranks protein on the lowest common denominator. So if a protein has 8/9 IAA’s (and it’s not histidine missing..) then the PDCAAS reflects it as a 0/100. Period.
To figure the PDCAAS:

  1. Get the amino acid information from the manufacturer. Some will give it to you willingly – generally those who have nothing to hide. Some put it on their product labels, some on their websites. But you cannot figure a PDCAAS without this information.
  2. Convert the IAAs into milligrams per gram of total protein for each amino acid. (Believe it or not, this is where the people beside me in class threw their pencils down in disgust..) Some companies provide their information in milligrams per 100 grams of protein, some provide per portion. This is simply a matter of doing the math to convert down into milligrams per gram of protein.
  3. Add methionine & cysteine and phenylalanine & tyrosine. This is due to the unique metabolism of these IAAs.
  4. Divide the milligrams of each IAA per gram of protein by the requirement for each IAA as set forth by the Institute of Medicine. It should be noted there was a standard set in 1985 and another set in 2005 in which the amounts increased dramatically. For example, the standard set in 85 for histidine was 0 mg/gm protein whereas in 2005 it was 18 mg/gm protein, and lysine went from 16 mg/gm protein to 51 mg/gm protein. Technically using either standard would be correct, but I will be using the 2005 standard in my calculations. (Chart given below.)
  5. Determine digestibility. This is where it gets questionable. This may be provided by the company.. if not, use data for the source protein as set by the Food and Agriculture Administration and World Health Organization. This is not an exact science.. make your best guess. (Chart given below.)
  6. Multiply digestibility score by lowest uncorrected ratio amino acid score found in step 4. This is the PDCAAS.

Example: Syntrax Nectar Medical Whey Protein Isolate Unflavored

  1. Get the amino acid information from the manufacturer.
    This is on the side of the container:
    Important Amino Acids Per 100 Grams of Protein
    Arginine 2.4 g
    Glutamine 7.4g
    Histidine 1.7g
    Isoleucine 6.7g
    Leucine 11.9g
    Lysine 9.7g
    Methionine 2.0g
    Phenylalanine 3.3g
    Threonine 7.2g
    Tryptophan 2.1g
    Valine 6.2g

    Pinked AAs are IAAs.

  2. Convert the IAAs into milligrams per gram of total protein for each amino acid.

    Histidine 1.7g / 100g protein

    I converted the 1.7g into milligrams first. 1000mg/1g = 0.017mg / 100g protein
    Divide the 0.017mg by 100 to get 1g protein = 17mg / 1g protein

    Isoleucine 67mg/gm protein
    Leucine 119mg
    Lysine 97mg
    Methionine 20mg
    Phenylalanine 33mg
    Threonine 72mg
    Tryptophan 21mg
    Valine 62mg

  3. Add methionine & cysteine and phenylalanine & tyrosine.

    Methionine 20mg + Cystenine 0mg = 20mg
    Phenylalanine 33mg + Tyrosine 0mg = 33mg

  4. Divide the milligrams of each IAA per gram of protein by the requirement for each IAA as set forth by the Institute of Medicine.

    IOM 2005 Requirements

    Histidine    18 mg/gm protein
    Isoleucine    25 mg/gm
    Leucine    55 mg/gm
    Lysine    51 mg/gm
    Methonine + Cysteine    25 mg/gm
    Phenylalanine + Tyrosine    47mg/gm
    Threonine    27mg/gm
    Tryptophan    7mg/gm
    Valine    32 mg/gm

    Calculations for Example:

    Histidine 17mg/gm     17 / 18 (IOM standard) = 0.94
    Isoleucine 67mg     67/ 25 = 2.68
    Leucine 119mg     119 / 55 = 2.16
    Lysine 97mg     97/ 51 = 1.90
    Methionine + Cysteine 20mg     20/25 =  0.8
    Phenylalanine + Tyrosine 33mg     33/47 = 0.7
    Threonine 72mg     72/27 = 2.67
    Tryptophan 21mg     21/7 = 3.0
    Valine 62mg     62/32 = 1.94

  5. Determine digestibility. There is not a digestibility score listed. So it’s time to look at the chart:

    Milk     95
    Casein     99
    Whey     99
    Egg white     98
    Soy     95-98

    This is whey protein isolate, so we will use the whey score.

  6. Multiply digestibility score by lowest uncorrected ratio amino acid score found in step 4. This is the PDCAAS.

    We take the lowest score from above (Phenylalanine + Tyrosine 33mg     33/47 = 0.7) and multiply that by .99 =
    .99 x .7 = 0.69

    To get a percent, multiply the 0.69 by 100.

    The PDCAAS for this product is 69%.


Now, I have to tell you — I expected to get a perfect score here, seeing it to be whey isolate. I’ve been glamoured into thinking whey isolate = perfect PDCAAS by the industry, but doing the math? It doesn’t add up. It could simply be because Syntrax did not put the values for Cysteine and Tyrosine on the label (or their website) but they are in the product. Or it could be that they simply are not in the product at all. So this is interesting to me on a couple of different levels. Very interesting. It makes me itch and want to go and check all of my supplements now. Seriously confuzzled here.

How seriously should we look at PDCAAS?

Well. If you are early out, it’s probably much more critical to look at it than if you are further out. Those who are struggling to get in all of their protein, who are actively starving themselves due to stringent restriction and healing from surgery? They probably should really watch this closely. Those patients should probably be sure they are choosing the best quality they can for the volume they can get down rather than “whatever I can get down is better than nothing” mentality.

Also those with restrictive diets — vegans, for example, should be aware of PDCAAS and protein quality.

However, those who are eating more normally, those who are further out and eating meat and only having protein supplements when needed probably don’t need to be as cautious as newbies should be. However, this doesn’t mean collagen bullets should be a sole source of protein, either.

In any case, PDCAAS is simply another tool to help patients, and hopefully their health care team, determine better quality products on the market for their needs.


Sourcework – 2011 ASMBS Allied Health Session, Protein Powders, Potions & Elixirs by Mary D. Litchford, PhD, RD, LDN

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9 Responses to “PDCAAS Math”

  1. Reggie Veil says:

    What is a good cuttoff for acceptable PDCAAS values? Thanks.

  2. Reggie Veil says:

    I forgot to say thank you for this excellent information. I’ve been wondering how to evaluate different protein sources in the powders. I’m pre-op and the first few weeks scare the hell out of me…

  3. Andrea says:

    Matter of opinion. Also, depends on medical needs.

    Personally, I wouldn’t go for anything below 95% as a protein supplement but that’s cause proteins are expensive.

    However, it should be noted that there are SOME reasons to look at some of the lower quality supplements like collagen, which aren’t as good at repairing muscle but better at things like skin and cartilage. If those were a factor, I’d be less inclined to look at the PDCAAS in these cases. These also provide a good nitrogen content, which is needed to help convert IAAs into the other amino acids as well.. so they can and do serve a purpose for a segment of the population.

  4. Hi Andrea – great post!
    Another complicating factor is that for most manufacturers, they are really only giving you the “typical amino acid profile.” Often whey suppliers may only assay on a periodic basis, and it is considered acceptable to publish levels this way (and I would agree). That said, proteins are natural products and the amino acid content for things like whey will vary from lot to lot. This is also of course true for food – no two cows, chicken or fish will have the same amino acid content.

    Kindest Regards,

  5. Mz. Puppie says:

    Interesting point about collagen being better at repairing skin than muscle. Can I extrapolate that to mean that collagen bullets might be a great idea for those who are recovering from plastic surgery?

  6. Jeanette says:

    The ASMBS covers the nitrogen aspect of collagen, too.

    “Caution should be used when recommending any type of
    collagen-based protein supplement. Although some commercial collagen products can be combined with casein or
    other complete proteins, the resulting combination might
    still provide insufficient amounts of several IAAs. These
    types of products are typically not considered “complete.”
    However, because collagen contains a high level of nitrogen
    within a small volume, it might be useful for the patient who
    is able to consume enough good-quality dietary protein to
    supply the needed IAAs, yet not be consuming enough total
    nitrogen to meet the nonspecific nitrogen requirement and
    achieve balance [171].”

    There was a collagen based protein Beth was talking about, wasn’t there, Andrea that had added tryptophan? I’m trying to remember where I saw her discuss that. I’m curious how much that ups the score.

    But, like I said in another thread, I tasted a collagen based protein shot and it tasted what I imagine ass would taste like. I’m not sure I would even want to choke those nasty things down even IF they were good for me.

  7. Val says:

    Sit beside me in math class pleeaaaase?
    I love how you are really giving factual information based in scientific evidence. It is what we need. There is so little factual info available to the normal postop. you breaking it down into understandable terms is a great help!
    Since I had surgery ( 9 years soon – 9/25/2002) I have seen so much posted by so many people that falls in the category of “repeated so often everyone know it is true” and so little that is actually evidence based.
    I’m also glad to see that your evidence backs up what I have always believed and followed as my eating habit, that if I get a good amount of protein from my diet – often 80-100 gms a day, I should be meeting my needs. I have had people try to convince me that they had it on absolute authority that we cannot absorb protein unless it is whey, and that I was risking death by malnutrition by not drinking protien. They never were able to provide any evidence to base it on other than rumor and specualtion. There is definately a place for protein supplementation, early post ops can’t consume enought to make it, people on liquid diets have to get it someplace and diet jello doesn’t do it. The people who NEED to rely on supplements need to have this kind of accurate and reliable information to make good decisions. THANK YOU !

  8. Pinkie says:

    I’m thinking too that collagen bullets might be useful post weight bearing workouts, I have been doing that to battle osteoporosis in lieu of yearly Reclast infusions for osteoporosis because of the possibility of increase femur fracture as a side effect, and did have some jaw bone death with it.

    I really appreciate that someone that takes such an interest in seeking information is so willing to share it.

  9. MacMadame says:

    When I was using collagen-based protein shots as one of my protein sources, my nails, hair and skin were fantastic.

    One of the issues I have with the PDCAAS system of scoring protein is that these collagen-based proteins are used in hospitals to keep up the protein levels of patients who receive all their nutrition from IVs. And they work! Yes, they work for patients who get protein from no other source to keep up their serum protein levels.

    Therefore, I think PDCAAS can’t be telling the whole story.

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