Is casein from cow's milk harmful to humans over one year of age?

Question

In the book Can We Live 150 Years?, author Mikhail Tombak, Ph.D. makes the following claim:

Casein is a protein needed by the calf for building its hoofs and horns. ... Human beings do not have hoofs or horns. Why would they need so much casein? (p.22)

Casein contained in milk is broken down in the stomach by rennet. Children one to two years old ... do not need casein. Their digestive system does not produce rennet anymore, and casein becomes indigestible, even poisonous. (p.23)

No source for this claim is cited. (In fact, the book is mysteriously missing a bibliography entirely!)

Is it true that casein "becomes even poisonous" to humans, specifically after the age of one or two years?

Answer 1

There is no reason to believe that casein cannot be digested by children or adults.

From "Gastrojejunal kinetics and the digestion of [15N]beta-lactoglobulin and casein in humans: the influence of the nature and quantity of the protein" (page 550)

casein was slowly recovered in the jejunum mainly in the form of degraded peptides efficiently absorbed in the upper part of the intestine

This paper is about different aspects of casein digestion, but the quoted passage shows that casein is degraded into peptides and absorbed in adults.

There is a study on the toxicity of casein to rats "Lethal Amounts of Casein, Casein Salts and Hydrolyzed Casein Given Orally to Albino Rats" which states

The lethal dose of casein given as an aqueous suspension intragastrically to albino rats was estimated to be well over 1000 g/kg administered over a period of 2 weeks but could not be definitely established because deaths were due in part to distilled water in the suspension.

So they had to feed the rats more than their own weight in casein to achieve toxic effects. In such extremely high doses pretty much anything can become toxic.

The part about casein being needed for hoofs and horns is either misleading or flat out invented by the author. The main purpose of milk is to provide nutrition. Casein is a family of proteins that can bind calcium and that are phosphorylated (see Wikipedia for more information). Proteins are a source of amino acids after digestion, and the caseins additionally provide calcium and phosphate. All of this is useful to humans, contrary to what the author writes.

If you take a look at the low-rated Amazon reviews you'll find that the author makes other extremely unlikely claims like the influence of zodiac signs on health. I wouldn't take anything serious that this author writes about health.

Answer 2

This is one of the most ridiculous claims I have ever seen.

First of all, there is not just one casein, caseins are a family of proteins.

Caseins are found in mammals milk in different proportion, generally quite high (that is why they are called caseins, from the Latin caseus, meaning cheese).

As the other answer points out, almost 50% of the protein content of human milk is made up of caseins during late lactation (from Human-milk proteins: analysis of casein and casein subunits by anion- exchange chromatography, gel electrophoresis, and specific staining methods.)

As for cow's milk:

Casein is the most important protein in bovine milk under both quantitative and nutritional aspects, as it represent approximately 80% of the total protein content (corresponding to 2.5–3%, w/v) and is rich in essential amino acids.

• Source: Quantification of bovine casein fractions by direct chromatographic analysis of milk. Approaching the application to a real production context.

So, essentially Dr. Tombak claims that all the people around the world who drink milk and eat cheese are very lucky and have not be killed by it so far...

Anyway, to the specific claim:

Casein is a protein needed by the calf for building its hoofs and horns. ... Human beings do not have hoofs or horns. Why would they need so much casein?

This does not really make sense. Proteins are digested and broken up into aminoacids, which are always the same 21, no matter the source of the protein. The fact that casein is found in hoofs and horns is absolutely irrelevant: calfs synthesise it, they don't use it directly from the proteins found in their mother's milk.

Chapter 23.1.1 of Biochemistry. (5th ed.) by Berg et al. explains this process.

Protein digestion begins in the stomach, where the acidic environment favors protein denaturation. Denatured proteins are more accessible as substrates for proteolysis than are native proteins. The primary proteolytic enzyme of the stomach is pepsin, a nonspecific protease that, remarkably, is maximally active at pH 2. Thus, pepsin can be active in the highly acidic environment of the stomach, even though other proteins undergo denaturation there.

Protein degradation continues in the lumen of the intestine owing to the activity of proteolytic enzymes secreted by the pancreas. These proteins, introduced in Chapters 9 and 10 (Sections 9.1 and 10.5), are secreted as inactive zymogens and then converted into active enzymes. The battery of enzymes displays a wide array of specificity, and so the substrates are degraded into free amino acids as well as di- and tripeptides. Digestion is further enhanced by proteases, such as aminopeptidase N, that are located in the plasma membrane of the intestinal cells. Aminopeptidases digest proteins from the amino-terminal end. Single amino acids, as well as di- and tripeptides, are transported into the intestinal cells from the lumen and subsequently released into the blood for absorption by other tissues

Source: The Digestion and Absorption of Dietary Proteins

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Finally, a remark on the author of the book, Mikhail Tombak, Ph.D.

I was wondering what subject his PhD was in, but couldn't really find much about it. Now, of course I may just need to search some more, but the best I could find was a copied-and-pasted-across-multiple-sites (including Start Healthy Life) biography stating:

Mikhail Tombak, Ph.D. graduated from the faculty of biology and chemistry of the Russian University. For many years he was the head of Center for Health Sciences in Moscow;

Needless to say there is no "Russian University" (e.g.)... and I could not find any evidence of a Center for Health Sciences in Moscow either.

Actually, if you Google for "Center for Health Sciences, Moscow Mikhail Tombak", you will only fall onto reviews of his books... so, well probably I would not really trust the source of the claim.

Answer 3

According to the American Journal of Clinical Nutrition, there is casein in human milk.

Total casein in human milk, as determined by the Kjeldahl method, varies during lactation; the casein content is approximately 20% of the total protein content in early lactation and 45% in late lactation.

So it's probably not poisonous.

Answer 4

There is an article by Michael Dye is repeated in several places on the Internet. It quotes a number of experts, such as Frank Oski

Frank Oski, M.D., author of Don't Drink Your Milk! is the Director of the Department of Pediatrics of Johns Hopkins University School of Medicine and Physician-in-Chief of the Johns Hopkins Children's Center. He is the author, co-author, editor or co-editor of 19 medical textbooks and has written 290 medical manuscripts.

In the first chapter of his book, Dr. Oski states, "The fact is: the drinking of cow milk has been linked to iron-deficiency anemia in infants and children; it has been named as the cause of cramps and diarrhea in much of the world's population, and the cause of multiple forms of allergy as well; and the possibility has been raised that it may play a central role in the origins of atherosclerosis and heart attacks."

[...]

Another outspoken critic of cow's milk is Dr. William Ellis, a retired osteopathic physician and surgeon in Arlington, Texas, who has researched the effects of dairy products for 42 years. Dr. Ellis is listed in Marquis' Who's Who in the East, Leaders of American Science, the Dictionary of International Biography and Two Thousand Men of Achievement. Dr. Ellis says dairy products are "simply no good for humans... There is overwhelming evidence that milk and milk products are harmful to many people, both adults and infants. Milk is a contributing factor in constipation, chronic fatigue, arthritis, headaches, muscle cramps, obesity, allergies and heart problems."

[...]

Dr. Christiane Northrup, a gynecologist in Yarmouth, Maine, states, "Dairy is a tremendous mucus producer and a burden on the respiratory, digestive and immune systems." Dr. Northrup says when patients "eliminate dairy products for an extended period and eat a balanced diet, they suffer less from colds and sinus infections."