What are milk proteins?

Casein and whey explained, from udder to intestines

Milk does not consist only of water and milk sugar. A large part are milk proteins. The two main families are caseins and whey proteins. Below you can read what they are, how they occur, what your body does with them and why you sometimes get symptoms. Clear, practical and with links to in-depth NooMooo blogs.

Brief explanation

Milk proteins are the proteins in milk. With cow's milk, roughly eighty percent casein and twenty percent whey. Caseins together form casein micelles that give milk its structure. Whey proteins, on the other hand, remain soluble in the aqueous phase of milk.

In simple language: think of casein as little balls floating through the milk and whey as the loose proteins in the milk liquid.

How are milk proteins formed in the udder

Milk proteins are made, packaged and excreted in the mammary gland cells of the udder. The process starts in the endoplasmic reticulum, where the cell builds the protein chains. Then these proteins go to the Golgi apparatus, which further processes and sorts them.

The caseins, meanwhile, bind to calcium phosphate and together form what are called micelles: tiny spheres whose exterior is made up of kappa casein. That layer keeps the micelle stable in the milk. Eventually, both the casein micelles and the loose whey proteins are packed into vesicles and delivered to the lumen of the mammary gland: that's the milk you eventually get in the glass.

In simple language
Think of the udder as a factory. First the cell builds the proteins, then they go out through the packing department in neat little packages. Casein clumps together into soft globules (micelles) with a protective layer, and whey remains loose in the milk fluid.

What types of milk protein are there

Casein

The casein group consists mainly of alpha s1-casein, alpha s2-casein, beta-casein and kappa-casein. Together, they form the micelle and are important for cheese making.

Complaint Opportunity: caseins belong to the most common allergens from cow's milk. They can also play along with sensitivity without allergy.

Whey Protein

The main whey proteins are beta-lactoglobulin and alpha-lactalbumin. They are in the watery phase and react differently to heating and digest than casein. Whey comes from the English word for whey.

Complaint Opportunity: both proteins are known allergens In cases of cow's milk protein allergy.

In simple language: casein is the club that clumps together, whey is the club that floats. Both can give symptoms, but in a different way.

What happens to milk proteins in your body

Milk proteins (casein and whey) each follow their own path once you ingest them. Below you can read about what happens step by step, and why that matters to how you feel after dairy.

What happens to milk proteins in the stomach

In the acidic environment of the stomach curdles casein: it forms a soft lump. As a result, it leaves the stomach slower and the release of amino acids occurs gradually. Whey Protein remain correct soluble and go faster through the stomach. That difference explains why casein is often more satiating, while whey is more quickly utilized.

What happens to milk proteins in the small intestine

Arrived in the small intestine take digestive enzymes such as trypsin and chymotrypsin take over. They cut both casein and whey into smaller pieces: peptides and amino acids. These are then absorbed through the intestinal wall and used by your body as building materials for muscles, enzymes and hormones, among others.

In simple language
Casein behaves like pudding: it stays in your stomach for a while and slowly releases nutrients. Whey is more like lemonade: it flows smoothly. In your gut, both are cut into small pieces, and those small pieces are exactly what your body can absorb and use.

Bioactive peptides

During cutting, bioactive peptides arise. Their significance varies by person and product. For most people, they are broken down further and simply absorbed. In simple language, this means that casein slows down and whey speeds up. Eventually, small pieces are released that your body uses as building blocks.

Why you may suffer from milk proteins

Cow's milk protein allergy

Then it responds immune system on casein or whey. That can fast are with skin rashes or tightness of the chest, or delayed With mainly intestinal complaints. Treatment: strictly avoid and guidance from physician or dietitian. Read the distinction with intolerance in What is the difference between cow's milk allergy and cow's milk intolerance.

Sensitivity without allergy

No allergy, but complaints such as bloated belly, fluctuating stools, fatigue, headache or skin complaints. The mechanism has not been proven one-to-one and appears to be related to barrier of the intestine, microbiome and low grade inflammation. Often a period of time helps cow's milk free and then targeted testing What you do tolerate. Follow our guide How to test whether or not you can tolerate cow's milk well.

In simple language: with allergy, your immune system is at work. With sensitivity, there is no allergy, but your body still does not react well to milk protein.

Does editing matter

Heating

Heating mainly changes whey proteins. Sometimes the sensitivity decrease, sometimes actually increase. It varies by person and product. Pasteurizing makes milk so not automatically safer For people with allergies or sensitivities.

Fermentation and ripening

Fermentation and maturation change especially lactose and taste. The proteins remain present. Therefore, if you are sensitive to milk proteins, you may also react to yogurt or aged cheese.

In simple language: warming or aging changes the proteins, but does not remove them.

A1 and A2 beta-casein in plain language

Beta-casein has variants, including A1 and A2. During digestion of A1 can the peptide BCM-7 release. Some studies suggest that A2 milk by some people milder feels in the abdomen. The evidence is not yet unequivocal. Think of it as a personal trial option, not as a guarantee.

In simple language: A2 may be nicer for some people, but it is not for everyone.

What does this mean practically for you

Know what you are testing

Start by getting clear on what triggers you. If you get symptoms from lactose-free dairy products, then this more often indicates a reaction to milk proteins. If your symptoms are triggered by products from goat or sheep, then lactose is more likely the trigger. Work step by step and test one variable at a time. Useful guide: How to test whether or not you can tolerate cow's milk well.

Lactose-free is not cow's milk-free

Lactose-free only says something about the sugar in milk. The milk proteins are still present and thus can still cause symptoms. If you are unsure what is going on with you, read the basics: What is lactose intolerance and What is cow's milk intolerance.

Choose alternatives that work for you

Plant-based options are often a safe and practical choice. Do pay attention to nutritional value: preferably choose varieties with added calcium and vitamin D. Labels remain important, especially with processed products. Additional help can be found in: Check the ingredient list.

Cheese issue, short and clear

Old, hard cheeses usually contain little lactose due to aging, but they continue to have milk protein. That means they sometimes go well with lactose intolerance, and can actually cause symptoms with cow's milk intolerance. For nuances by cheese type: Which cheeses contain high or low levels of lactose.

Using supplements smartly

Lactase only works against lactose. It does nothing against milk proteins and thus does not help with cow's milk intolerance. Use it where appropriate and read more about dosage and forms in: What are lactose intolerance pills.

Frequently Asked Questions

What are milk proteins

Milk proteins are the proteins in milk. In cow's milk, about eighty percent consists of casein and twenty percent from whey. Casein forms the structure of milk, while whey protein remains dissolved in the liquid part.

What is the difference between casein and whey

Casein Clumps together in the form of micelles and gives milk firmness. Whey Protein such as beta-lactoglobulin and alpha-lactalbumin, on the contrary, remain dissolved in the aqueous phase. Both types of proteins can cause symptoms in some people.

How are milk proteins formed in the udder

In the mammary gland cells, proteins are built up and then packaged into small vesicles. Casein forms micelles along with calcium, while whey proteins remain loose in the fluid. Both are excreted through the mammary gland into the milk.

What happens to milk proteins in your stomach and intestines

In the stomach curd casein into a soft lump, digesting it slowly. Wei remains liquid and passes more quickly to the small intestine. There, both types of proteins are broken down by enzymes into smaller pieces and amino acids, which the body can absorb.

Can you suffer from milk protein without allergy

Yes, you can. Some people experience symptoms such as abdominal bloating, fatigue, skin problems or headaches, without an allergy. This may have to do with gut function, the microbiome or sensitivity to certain protein fragments.

What is cow's milk protein allergy in brief

At a cow's milk protein allergy reacts it immune system on casein or whey. Symptoms may occur immediately, such as skin rashes or tightness of the chest, or later, with abdominal pain or diarrhea, for example. Treatment is strict avoidance of cow's milk protein, under the guidance of a doctor or dietician.

Helps heat or pasteurize against complaints from milk proteins

Heating mainly changes the structure of whey proteins. For some people, that makes a difference in how they tolerate it, but it's not a guarantee. Pasteurizing does not remove the proteins and thus does not automatically make milk suitable for people with allergies or sensitivities.

Do fermentation and aging do anything to milk proteins

Fermentation and maturation break especially lactose off and change the taste. The proteins however, remain present. Therefore, products such as yogurt or aged cheese can still cause symptoms in cases of sensitivity to milk proteins.

Is A2 milk more tolerable than regular milk

Milk contains varieties of beta-casein: A1 and A2. Digestion of A1 may release a substance (BCM-7) that causes symptoms in some people. A2 milk is sometimes better tolerated, but the evidence is not yet conclusive. It may be an option to try out for yourself.

Is lactose-free the same as cow's milk-free and do lactase supplements work against milk proteins

Lactose-free means that the milk sugar (lactose) has been removed or broken down. The milk proteins remain present. Lactase supplements help only with lactose and have no effect on milk proteins. In cases of sensitivity to milk proteins are cow's milk free or vegetable alternatives needed.

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With this foundation, you can targeted testing, smarter choices and your own threshold Finding. On NooMooo you will find honest explanation, familiar stories and practical tips in one place. That saves searching and especially hassle for your belly.

Note: this blog is informational. I am not a doctor and do not give medical advice. If in doubt, contact your doctor or dietician.