Lactose Intolerance vs A1 Beta Casein Protein Intolerance

Kate DiPrima for Beta A2 Australia – Oct 2021

Dairy foods including milk, cheese and yoghurt provide essential calcium and protein and is recommended to be included as part of a healthy diet. However for a growing number of people, consuming dairy foods can cause many symptoms ranging from skin conditions such as eczema, to gastrointestinal symptoms of diarrhoea or constipation. Symptoms are associated with either an allergy to the dairy protein involving the immune system, or an intolerance to the dairy protein or the dairy sugar known as lactose.

Lactose is present in all mammalian milk including human milk.  The lactose molecule is a disaccharide represented as 2 sugars bound together by 1 bond – the sugars are glucose & galactose. The Lactose molecule is the same (uniform) across all mammals however the amount present varies between 2-9%.  Human milk lactose levels are approx. 7%[1], while milk (bovine or cows) is between 4-5%[2].  Infant formula based on cow’s milk has adjusted levels of lactose to be aligned with levels in human milk.

68% of the world’s population identify themselves as intolerant to dairy[3] and most people believe their intolerance is due to lactose. But what if that’s not the case?

True lactose intolerance, where the body is unable to digest the dairy sugar, is less common than is widely perceived, and is only one potential cause of cows’ milk intolerance. There is increasing scientific evidence that the A1 beta-casein protein found in standard dairy milks may be associated with cows’ milk intolerance.

In humans, digestion of the A1 beta-casein protein found in regular dairy products produces a peptide (smaller protein) known as beta-casomorphin-7 (BCM-7). BCM-7 activates opioid receptors throughout the gastrointestinal tract and body which can mimic the symptoms of lactose intolerance in sensitive systems. In dairy products that only contain the A2 beta- casein protein, BCM-7 is not produced and therefore can be gentler on the gut.

Human research involving a double-blind, randomized cross-over study showed that participants consuming A1 beta-casein type cows’ milk experienced statistically significantly looser stools compared with those receiving A2 beta-casein milk. Additionally, a statistically significant positive association between abdominal pain and stool consistency was observed when participants consumed the A1 but not the A2 diet[4].

Those babies, children or adults  diagnosed by a health care professional with a cow’s milk protein allergy,  need to avoid all cow’s milk proteins including A1 and A2. A health care professional such as Paediatrician, GP or specialized Dietitian can help determine whether symptoms are associated with an allergy or intolerance. There are a small number of babies that are lactose intolerant and are unable to breast feed.  They must have their own specialised formula.  Equally there are those that are allergic to cow’s milk all together and must avoid all dairy products.

For the vast majority of babies, they are able to breast feed and digest the lactose.  It is when they transfer to regular cow’s milk after breastfeeding that they experience intolerance symptoms, for example bloating and constipation. It is at this point that they attribute these symptoms to a component found in cow’s milk (which could be various components in the milk including Lactose).   The key thing to remember is that the lactose molecule is exactly the same in human milk and cow’s milk.  Perhaps there are other factors contributing to symptoms including ethnicity, a drop in lactase production or the status of the gut[5]; however it could equally be attributed to the presence of the A1 beta casein protein, which is absent in human milk.

Milk and dairy intolerance is a complex problem of importance both to public health and individual health. It is clear that lactose malabsorption (and consequent symptoms) is one element of the syndrome, but it is also evident that there are other factors that play an important role. The potential role of A1 beta-casein is arguably the prime candidate requiring closer scrutiny if understanding is to be advanced[4].

[1] Jenness R. The composition of human milk. Semin Perinatol. 1979 Jul;3(3):225-39. PMID: 392766

[2] Steve Hertzler, Dennis A. Savaiano, Abby Dilk, Karry A. Jackson, Sinead N. Bhriain, Fabrizis L. Suarez, Chapter 40 – Nutrient Considerations in Lactose Intolerance, Editor(s): Ann M. Coulston, Carol J. Boushey, Mario G. Ferruzzi, Linda M. Delahanty, Nutrition in the Prevention and Treatment of Disease (Fourth Edition), Academic Press, 2017, Pages 875-892, ISBN 9780128029282, Adv. Nutr. 2017 Sep; 8(5): 739–748.

[3] Storhaug CL, Fosse SK, Fadnes LT. Country, regional, and global estimates for lactose malabsorption in adults: a systematic review and meta-analysis. The Lancet. Gastroenterology & Hepatology. 2017;2(10):738–746.

[4] Milk Intolerance, Beta-Casein and Lactose.  Sebely Pal, Keith Woodford, Sonja Kukuljan, Suleen Ho.  Nutrients. 2015 Sep; 7(9): 7285–7297

[5] Lactose Intolerance. Mayo Clinic


Special Thanks to Dietitian Kate DiPrima for her contributions to this article.

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