Milk Intolerance May be Caused by A1 Beta-Casein

Digestive issues that result from milk consumption are often attributed to lactose intolerance, but research indicates that it may be the result of an intolerance to a specific type of protein found in some types of cow’s milk; specifically A1 beta-casein.

Casein and whey are the two primary proteins found in milk, with casein accounting for ~ 80 % of the protein in milk. Approximately 30% of the protein in milk is beta-casein.

There are two variants of beta-casein; A1 and A2, however before cows were domesticated, they only produced milk that only contained the A2 form of beta-casein[1,2]. Older breeds of cows such as most Jerseys, Guernseys, Brown Swiss, Normandes, as well as most of the cows in Asia, Africa and southern Europe[2] produce milk with the A2 variant of beta-casein, as do goats, sheep, donkeys, yaks, camel and buffalo [2]. In addition, human milk contains A2 beta-casein.

It is thought that ~8,000 years ago, a single-gene mutation occurred in Holsteins which resulted in the production of the A1 beta-casein protein in this breed. This novel gene variant was passed on to other northern European breeds of cows, including Friesian, Ayrshire and British Shorthorn since Holsteins were bred with them to improve milk production[2]. 

Today’s Holstein breed is the most common dairy cow in the US, Canada, Australia and northern Europe and carries both A1 and A2 forms of beta casein in approximately equal amounts[2].

Milk intolerance may not always be due to lactose intolerance, but due to intolerance to milk containing A1 beta-casein.

Note: Primary lactose intolerance is a result of a lack of the enzyme lactase, which is genetic in origin. This is a permanent condition. Secondary lactose intolerance is temporary and the result of being sick with something that causes diarrhea which sloughs off the lactase from the wall of the intestine. Genuine lactose intolerance can be tested with a hydrogen breath test.

Research suggests that A1 beta-casein protein may be at the root of stomach pain and other gastrointestinal (GI) symptoms associated with consumption of milk from A1 cows and which closely resemble lactose intolerance. These symptoms are not present when consuming milk from cows that only produce A2 beta-casein. Food-derived peptides such as β-casomorphins and others are known to have different effects on the intestines, including the secretions of the stomach and pancreas, as well as gut motility [3]. Studies have found that a peptide called β-(beta) casomorphin (BCM-7) may be behind stomach pain and other symptoms associated with milk containing A1 beta-casein.

The Difference Between A1 and A2 Beta-Casein

If one thinks of proteins as chains of amino acids strung together like train-cars in a train, each one of the ‘cars’ represents a different amino acid.  In the older A2 beta-casein variant, the ‘car’ which occupies the 67th position is an amino acid called proline, but in the newer A1 beta-casein variant, the amino acid in the 67th position is histidine. When milk with A1 beta-casein is digested, the histidine bond breaks, resulting is a peptide made up of 7 amino acids, called β-(beta) casomorphin-7 (BCM-7).

β-(beta) casomorphin-7 (BCM-7) is a naturally occurring opioid peptide, with a structure similar to morphine and is known to bind to opioid receptors [3]. What effect does BCM-7 have on the body as a result of binding with these opioid receptors?

A 2015 review paper cites research demonstrating that milk containing A1 beta-casein increases GI transit time (the amount of time that it takes for food to go through the GI tract) which means in slows it down, and in animal studies, increases inflammatory markers significantly more than A2 beta-casein containing milk[5]. In a small, double-blinded, randomized crossover study from 2014 with 41 subjects, it was found that participants consuming A1 beta-casein cow’s milk had significantly softer stools, more bloating and more abdominal pain than those drinking A2 beta-casein milk [6]. In another unrelated double-blind, randomized, crossover trial from 2016 with 45 Chinese participants with self-reported intolerance to cow’s milk drank  250 mL of either A1/A2 or A2 milk following each of two meals over a 14-day period. When drinking the A1 beta-casein milk, there was an increase in transit time and in GI inflammation, and a worsening of digestive discomfort [7] as well as an increase in inflammatory markers such as IgG, IgE, and IgG1. These were significantly lower in those that drank A2 milk [7].

Addendum (July 22, 2019): *there has been some anecdotal evidence that people with arthritis do considerably better when they do not consume casein (see Arthritis Foundation website).

In a large scale 2017 randomized cross-over design follow-up study, 600 adult who reported lactose intolerance and digestive discomfort following milk consumption were assigned over a 7-day period to consume either 300 mL of conventional milk containing both A1 and A2 beta casein, or only A2 milk. Results indicated digestive symptoms were markedly reduced after consuming A2 milk versus conventional milk [8].

Healthcare professionals have often assumed (without giving people hydrogen breath tests to confirm it) that people with GI symptoms related to consuming dairy products have lactose intolerance, when it is possible that the symptoms could be related to intolerance of A1 beta-casein.

Concerning to those with histamine-intolerance, including those with Mast Cell Activation Disorder (MCAD) who need to lower their intake of histadine-containing foods and histamine-liberators [9] may unknowingly be adversely affected by milk commonly available in the US, Canada, Australia and northern Europe that contains A1 beta-casein, as when it is digested it produces betacasomorphin-7 (BCM-7), a potent histamine liberator. The most well-known Histamine Intolerance Food Compatibility List from the Swiss Histamine Intolerance Group (SIGHI) lists milk as producing a low reaction — perhaps because the milk available in Central Europe, as in southern Europe, contains A2 beta casein, and not A1 beta-casein as in North America, Australia and northern Europe [10]. Those with histamine-intolerance in the US and Canada, for example and other countries with A1 beta-casein in dairy need to be aware that the milk and the hard cheeses listed as being “well-tolerated, no symptoms expected at usual intake” does not apply to the milk and cheese available to them.

Final Thoughts…

While much research has yet to be done to determine the extent that A1 beta-casein proteins impact human health, those with suspected lactose intolerance who continue to have symptoms while consuming lactose-free milk and low-lactose products such as yogurt and hard cheese, should try eliminating milk produced at ordinary large-scale dairies that have milk containing both A1 and A2 beta-casein to see if their symptoms improve.  As a substitute, they could use goat milk or buffalo milk, or find small, local dairies that use “heritage herd” cows, such as specific species of Jerseys, Guernseys, Brown Swiss, and Normandes that only produce milk with A2 beta-casein.

Note: My tried and true recipe for making homemade goat or A2 yogurt in an oven or crock-pot using a temperature controller, as well as turning it into thick Greek yogurt is posted here.

Those with histamine-intolerance in the US, Canada and Australia might feel better avoiding milk, cheese, and yogurt from conventional dairies, as these contain A1 beta-casein, which are high histamine liberators. After a period of dairy avoidance to enable mast cells to calm, dairy products from “heritage herd” cows can then be trialed.

NOTE: Butter and full-fat (whipping) cream are entirely fat, and as such do not contain either A1 or A2 beta-casein proteins. These would be fine to consume regardless of which dairy they were from.

More Info?

If you have food allergies or food intolerances, including what you thought was lactose intolerance, or have been diagnosed with histamine-intolerance or Mast-Cell Activation Disorder (MCAD), I can help.

You can find out more about the packages and hourly consultations I offer under the Services tab or by clicking here. If you would like further information, please send me a note using the Contact Me form above and I will reply as soon as I can.

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LEGAL NOTICE: The contents of this blog, including text, images and cited statistics as well as all other material contained here (the ”content”) are for information purposes only.  The content is not intended to be a substitute for professional advice, medical diagnosis and/or treatment and is not suitable for self-administration without the knowledge of your physician and regular monitoring by your physician. Do not disregard medical advice and always consult your physician with any questions you may have regarding a medical condition or before implementing anything  you have read or heard in our content.


  1. Ware M, Metropulos M, Medical News Today, A2 milk: What you need to know, July 25, 2017,
  2. Pasin G. A2 milk facts. California Dairy Research Foundation website. Published February 9, 2017.
  3.  European Food Safety Authority. Review of the potential health impact of β-casomorphins and related peptides. EFSA J. 2009;7(2):1-107.
  4. Kurek M, Przybilla B, Hermann K, A naturally occurring opioid peptide from cow’s milk, beta-casomorphine-7, is a direct histamine releaser in man, Int Arch Allergy Immunol. 1992;97(2):115-20.
  5. Pal S, Woodford K, Kukuljan S, Ho S. Milk intolerance, beta-casein and lactose. Nutrients. 2015;7(9):7285-7297.
  6.  Ho S, Woodford K, Kukuljan S, Pal S. Comparative effects of A1 versus A2 beta-casein on gastrointestinal measures: a blinded randomised cross-over pilot study. Eur J Clin Nutr. 2014;68(9):994-1000.
  7. Jianqin S, Leiming X, Lu X, Yelland GW, Ni J, Clarke AJ. Effects of milk containing only A2 beta casein versus milk containing both A1 and A2 beta casein proteins on gastrointestinal physiology, symptoms of discomfort, and cognitive behavior of people with self-reported intolerance to traditional cows’ milk. Nutr J. 2016;15:35
  8. He M, Sun J, Jiang ZQ et al, Effects of cow’s milk beta-casein variants on symptoms of milk intolerance in Chinese adults: a multicentre, randomised controlled study. Nutr J. 2017 Oct 25;16(1):72.
  9. Molderings GJ, Brettner S, Homann J, Afrin LB. Mast cell activation disease: a concise practical guide for diagnostic workup and therapeutic options. J Hematol Oncol. 2011;4:10. Published 2011 Mar 22. doi:10.1186/1756-8722-4-10
  10. Lamprecht H, Swiss Interest Group Histamine Intolerance (SIGHI), Histamine Intolerance Food Compatibility List, &

This article is based in part on material by Judith C. Thalheimer, RD, LDN, Is A2 Milk the Game-Changer for Dairy Intolerance?Today’s Dietitian, Vol. 19, No. 10, P. 26

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Lactose Intolerance


Lactose is the sugar found in milk and milk products. It is also added to some processed and prepared foods such as salad dressings. An enzyme called lactase is needed for your body to break down (digest) lactose.

Primary lactose intolerance occurs when your body does not have enough lactase — which can occur because your body does not make it. Certain ethnic populations have a higher likelihood of having primary lactose intolerance. In North America, adults lactose intolerance has been reported at 90% of Asians, 80% of First Nations, 75% of Blacks, 50% of Hispanics, and 21% of Caucasians 1. As high as 60-80% of Ashkenazi Jews (Jews of Eastern European background) have primary lactose intolerance 2

Secondary lactose intolerance occurs as a result of something else such as in inflammatory bowel disease, such as Crohn’s or Colitis. Celiac disease (antibody mediated gluten intolerance) or those with Celiac disease who have not been strictly following a gluten-free diet may also have secondary lactose intolerance. In these cases, the villi of the intestine (little hair-like projections that increase the surface area of the intestine) which contain the lactase needed to break down the lactose become damaged, resulting in lactose intolerance.  For those with inflammatory bowel disease or Celiac disease, once their disease is better managed,  the villi in their intestines heal, making them able to digest lactose again. Even a bout of stomach flu can result in temporary lactose intolerance.

Congenital Lactose Intolerance – In rare cases, lactose intolerance is cause by a defective gene that is passed from the parents to a child, resulting in the complete absence of lactase in the child. This is referred to as congenital lactose intolerance.



In those without lactose deficiency, the body breaks down the lactose taken in through the diet into smaller parts for digestion and absorption. Without the lactase enzyme, or enough of this enzyme, the lactose passes into your large intestine undigested, and there it is fermented by bacteria which may result in symptoms such as:

  • bloating
  • gas
  • cramping
  • nausea
  • diarrhea
  • weight loss (in children)

The severity of these symptoms depends on the amount of lactose eaten and the amount of lactase enzyme that the body produces. Most people with lactose intolerance can tolerate some lactose in their diet.

How Is Lactose Intolerance Diagnosed?
Lactose Intolerance Test

This blood test measures your body’s reaction to a liquid that contains high lactose levels.

Hydrogen Breath Test

This test measures the amount of hydrogen in your breath after consuming a drink high in lactose. If your body is unable to digest the lactose, the bacteria in your intestine will break it down instead. The process by which bacteria break down sugars like lactose is called fermentation. Fermentation releases hydrogen and other gases. These gases are absorbed and eventually exhaled. If you aren’t fully digesting lactose, the hydrogen breath test will show a higher than normal amount of hydrogen in your breath.

Stool Acidity Test

This test is more often done in infants and children. It measures the amount of lactic acid in a stool sample. Lactic acid accumulates when bacteria in the intestine ferment the undigested lactose.

Managing Lactose Intolerance

Those with lactose intolerance benefit from reducing the amount of lactose in their diet.

While you expect to find lactose in milk products, it is often added as an ingredient to foods and beverages you might not think have lactose. Be sure to read the ingredient list on product label to find out if the product contains an ingredient that contains lactose — such as:

  • milk
  • milk solids
  • whey
  • lactose
  • curds
  • cheese flavour
  • malted milk
  • non-fat milk solids
  • buttermilk
  • cream
  • non-fat milk powder


Prepared foods may also contain lactose, including:

  • store bought gravy or sauce mixes
  • vegetable or chip dips
  • soups
  • chips or snack crackers (e.g. cheese or ranch flavoured)
  • sugar substitutes made with lactose (e.g. Equal®)
  • artificial whipped toppings
  • powdered meal replacement supplements
  • hot chocolate mixes
  • cream-based liqueurs

Note: Products that contain lactic acid, lactalbumin, lactate and casein do not contain lactose.

Limiting, Rather than Avoiding Lactose

Some people are able to tolerate certain lactose-containing foods while other people with lactose intolerance cannot.

Limit your intake of foods that cause you discomfort.

hard cheddar

Once your symptoms have improved significantly, try adding in small amounts (60-125mL or 1/2 cup) of lower lactose foods such as:

  • hard, aged cheese (cheddar, Swiss, Parmesan)
  • yogurt
  • chocolate milk
  • pudding
  • sour cream
  • cottage cheese

If these amounts cause you discomfort, then try eat less.

Greek yogurt
Lactose Free & Lactose Reduced

In Canada, ”lactose-free” means that there is no detectable lactose in the food.  ”Lactose-reduced” means that at least 25% of the lactose in the product has been removed.

Calcium and Vitamin D

Many foods that contain lactose are also important sources of calcium and vitamin D, so if you avoid lactose-containing foods, be sure to include other sources of these nutrients, such as the following lactose-free or lactose-reduced products, preferably fortified with calcium, such as:

  • lactose-hydrolyzed milk (e.g. Lactaid®, Lacteeze®)
  • soy beverage
  • rice beverage
  • casein or soy-based products in place of cheese
  • yogurts with live bacterial cultures or lactose-reduced yogurts
Calcium & Vitamin D

It is important that if you are lactose intolerant to be sure to get enough Calcium and Vitamin D.

Calcium is a mineral that helps you build and maintain strong bones and teeth, and is also used in other parts of your body — to help your muscles work and is involved in maintaining your heartbeat. Adequate calcium intake throughout your life can help to prevent osteoporosis, a disorder that causes thinning of the bones until they are weak and fracture easily or break. Women are at greater risk of developing osteoporosis than men, particularly after menopause, because estrogen levels which act to maintain bone are reduced.

Lactose-free sources of vitamin D include fish, liver and egg yolks.


Being lactose intolerant does not mean you can’t ever have dairy – hard cheese and yogurt are naturally low in lactose and reduced lactose milk can be purchased at most grocery stores. Some people may not have any symptoms at all from regular milk or cream, provided they only have a small amount. If 1/2 cup (125ml) causes you discomfort, then try 1/4 cup.

Finally, remember that Calcium and Vitamin D can be found in other foods besides dairy, such as canned sockeye salmon. Don’t forget that the bones are the best sources, so mash them finely and eat them along with the rest.




  1. Scrimshaw NS, Murray EB. The acceptability of milk and milk products in populations with a high prevalence of lactose intolerance. Am J Clin Nutr. 1988;48(4 Suppl):1079. Available at: Accessed on March, 6, 2015.
  2. Heyman, MB. Lactose intolerance in infants, children, and adolescents. Pediatrics 2006;118(3):1279-1286. Available at: full Accessed on February 23, 2015.