# what is the amino acid breakdown of milk protein? **URL:** \ **Category:** Factual Questions\ **Created:** [October 24, 2003, 2:55am UTC](https://boards.straightdope.com/t/what-is-the-amino-acid-breakdown-of-milk-protein/209244 "2003-10-24T02:55:33Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Wesley\_Clark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wesley_clark/32/20581_2.png) [@Wesley\_Clark](https://boards.straightdope.com/u/Wesley_Clark)\ **Post date:** [October 24, 2003, 2:55am UTC](https://boards.straightdope.com/t/what-is-the-amino-acid-breakdown-of-milk-protein/209244/1 "2003-10-24T02:55:33Z")
of the 20 amino acids, how many of each are present in the 8 grams of protein per serving of milk? ---
**Author:** ![Nametag](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nametag/32/406_2.png) [@Nametag](https://boards.straightdope.com/u/Nametag)\ **Post date:** [October 24, 2003, 5:31am UTC](https://boards.straightdope.com/t/what-is-the-amino-acid-breakdown-of-milk-protein/209244/2 "2003-10-24T05:31:19Z")
According to [this site](http://www.priyachem.com/casesoy.htm), the following percentages are present in casein, the main protein in milk: L-ASPARTIC ACID 13.00 L-GLUTAMIC ACID 25.39 L-HYDROXYPOLINE 4.39 L-VALINE 3.52 L-ISOLEUCINE 3.68 L-PHENYLALANINE 3.47 L-HISTIDINE 1.67 L-THREONINE 4.77 L-PROLINE 1.47 L-ALANINE 3.89 L-METHIONINE 1.72 L-TRYPTOPHAN 0.87 L-ARGININE 2.09 L-SERINE 4.85 L-CYSTINE 1.46 L-LEUCINE 5.98 L-GLYCINE 10.08 L-TYROSINE 3.31 ---
**Author:** ![Bob55](https://avatars.discourse-cdn.com/v4/letter/b/e9c0ed/32.png) [@Bob55](https://boards.straightdope.com/u/Bob55)\ **Post date:** [October 24, 2003, 5:50am UTC](https://boards.straightdope.com/t/what-is-the-amino-acid-breakdown-of-milk-protein/209244/3 "2003-10-24T05:50:05Z")
My first guess was that it would be the same percentages as our bodies, but this doesn’t seem to be the case. [www.ars.usda.gov/is/AR/archive/may98/milk0598.pdf](http://216.239.39.104/search?q=cache:QRGdoI-dQS0J:%5Burl)]This site claims that milk is very similar between mammals, and says > [@](#): > > Three amino acids — glutamate, leucine, and proline — make up 40 percent of the total amino acids in all animals’ milk. > > While all primates — humans, chimps, and apes — have very similar milk components, human milk has the highest cystine content, with the great apes coming in second. > > Both tiger and house cat milks have a high arginine content. Other amino acids are found in milk, such as taurine. I’ll try to find out the actual percentages. ---
**Author:** ![Bob55](https://avatars.discourse-cdn.com/v4/letter/b/e9c0ed/32.png) [@Bob55](https://boards.straightdope.com/u/Bob55)\ **Post date:** [October 24, 2003, 6:05am UTC](https://boards.straightdope.com/t/what-is-the-amino-acid-breakdown-of-milk-protein/209244/4 "2003-10-24T06:05:18Z")
Using **Nametag’s** data we can calculate the # of molecules of each amino acid using their[molecular weight.](http://www.bioscience.org/urllists/aminacid.htm) For example, in 8g of milk protein approximately 25% is glutamic acid (Mw = 147.13) so 25% \* 8g \* (1 mole/147.13g)\* (6.02x10^23 molecules glutamic acid/1 mole) = 8.18x10^21 molecules of glutamic acid in 8g of milk protein (caesin). Taking a smaller one like proline (1.47%), you get 6.1x10^20 molecules. ---
**Author:** ![Popup](https://avatars.discourse-cdn.com/v4/letter/p/94ad74/32.png) [@Popup](https://boards.straightdope.com/u/Popup)\ **Post date:** [October 24, 2003, 12:47pm UTC](https://boards.straightdope.com/t/what-is-the-amino-acid-breakdown-of-milk-protein/209244/5 "2003-10-24T12:47:54Z")
I think you have to specify which kind of milk. I would assume cow, but some of the links above treat other kinds. > [@](#): > > \*Originally posted by Bob55 \* > **This site claims that milk is very similar between mammals, and says** Not according to Harold McGee, who wrote the highly recommended _On Food and Cooking_. He claims that cow milk contains three times as much protein as human milk (8% vs 2.5 or so). Also, the protein in cow milk is mainly (~80% IIRC) casein, whereas human milk has more (~60% again IIRC) whey. A (cow) calf doubles in weight in 50 days, whereas it takes something like 100 days for a human baby to double in weight. (I don’t have the book here, so all the figures are from memory - Salt to taste.) ---
**Author:** ![Epimetheus](https://avatars.discourse-cdn.com/v4/letter/e/c4cdca/32.png) [@Epimetheus](https://boards.straightdope.com/u/Epimetheus)\ **Post date:** [October 24, 2003, 1:08pm UTC](https://boards.straightdope.com/t/what-is-the-amino-acid-breakdown-of-milk-protein/209244/6 "2003-10-24T13:08:22Z")
I don’t have a cite handy but I have heard that milk, for children if not adults, is not a good source for complete proteins. Milk apparently lacks a protein necessary for proper brain development in children, and feral children like Anna and Genie that were fed nothing but milk did not develop properly because of that. (probably contendable, due to the severe isolation of these two girls) (According to my Sociology teacher anyhow) I personally would be wary of that statement because many babies are fed breastmilk and have developed just fine through the ages. Whether or not they were fed nothing BUT breastmilk I do not know. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [October 24, 2003, 3:57pm UTC](https://boards.straightdope.com/t/what-is-the-amino-acid-breakdown-of-milk-protein/209244/7 "2003-10-24T15:57:11Z")
Couple of things. First, while casein is the main protein in milk, even the casein has a number of different components. Here’s a [PDF file](http://www.nationaldairycouncil.org/nutrition/products/table15.pdf) from the National Dairy Council giving some breakdowns. Even these are simplified, as there are at least a half-dozen immunoglobulins. Milk is not at all similar among mammals, as must be the case since the needs are so very different. For example, humans have the highest percentage of lactose in their milks, at 7%. Cows have 5%, but some of the sea mammals have none at all, instead having 35% fat for energy, compared to 4% for cows, which is just slightly less than in breastmilk. **Epimetheus** , you are correct that cow’s milk is not perfectly suitable for human babies, which is why formulas have been developed, but if nothing else is available it’s the best substitute. You do seem to be confusing breastmilk with cow’s milk, though. Obviously all mother’s milk is perfectly suited for sole consumption until weaning for their own babies. Also note that **nametag’s** cite is for a casein-based protein supplement, not for protein straight out of the cow. OK, now to answer the question. [Amino Acid Distribution in Milk](http://www.nationaldairycouncil.org/nutrition/products/TABLE16.pdf)