True or False: There is Good A2 and Bad A1 Casein and Eating the too Much A1 Containing Regular Dairy is Going to Make You Fat, Sick and Insulin Resistant!

"A1 beta-casein is a health risk regular dairy consumers are exposed to." Truth or science fiction even Marvel would be ashamed to propagate?
It sounds like yet another of these Internet humbug myths, but you will hardly believe it, there is actually a recent study investigating the differential effects of A1 vs. A2 beta-casein - and it's not a rodent study (Ho. 2014)!

The scientists from the Curtin University were intrigued by the previous in-vitro and animal studies which suggest that digestion of A1 but not A2 beta-casein affects the gastrointestinal motility and inflammation through the release of beta-casomorphin-7.

In their latest study, Ho, Woodford, Kukuljan & Pal did thus aim to "evaluate differences in gastrointestinal effects in a human adult population between milk containing A1 versus A2 beta-casein." (Ho. 2014)
You can learn more about dairy at the SuppVersity

Dairy Has Branched-Chain Fatty Acids!

Is There Sth. Like a Dairy Weight Loss Miracle?

Foods, Not Ma- cronutrients Build Healthy Guts

Lactulose For Your Gut & Overall Health

Is There a "Fat Advantage" for Dairy Lovers

Dairy, Diabetes, Estrogen, IGF-1, Cancer & More
Before we get to the results let's briefly review why these differential gastrointestinal effects would even be relevant. So let's see what Ho et al. have to say about that:
"Beta-casein is the second most abundant casein type in cows’ milk and comprises ~ 30% of total milk protein. There are two families of beta-casein proteins, known as A1 and A2 beta-casein ‘types’. The A1 type variant arose in European herds from the original A2 type ~ 5000–10 000 years ago from a Proline 67 to Histidine 67 point mutation. In countries that have dairy cows of northern European ancestry, the relative proportions of the co-dominant A1 to A2 beta-casein alleles are typically 1:1 in cows, which then produce the same ratio of A1 to A2 beta-casein in milk. This tends to be lower in breeds from Southern Europe." (Ho. 2014)
As you can see, it's hard to tell, how much A1 "your" milk actually contains. In view of the fact that the A2-only cattle is less productive, you can be pretty certain, though, that the milk you can buy at the supermarket contains significant amounts of A1 beta-casein. Accordingly, there will be a certaion amount of A1 that is converted to the bioactive opioid peptide betacasomorphin-7 (BCM-7) whenever you drink a glass of milk (compared to A1, A2 beta-casein releases much less and probably minimal amounts of BCM-7 under normal gut conditions (De Noni. 1999; Schmelzer. 2007;  Cielinkska. 2012)

So BCM-7 is the villain, here?

BCM-7 is a mu-opioid receptor ligand. It will dock to the mu-opioid receptors which are expressed widely throughout your body - most prominently, obviously, to those in your gut.

If you are looking for something to freak out about, how about homogenization? Try my article "New Research Fuels the Flames on Concerns About Ill Health Effects of Homogenized Milk" | learn more.
From rodent studies we know that the increased transit time and potential downstream on the release and stability of incretin hormones (GLP1, GIP & co), which are involved in the release of insulin and appetite control (Barnett. 2014). In that, the degradatin of GLP1 & co is rather collateral damage that occurs, when the body produces an enzyme to break down the BCM-7 peptides in the gut.

The degradation of "satiety hormones" is yet only one negative side effect Barnett et al. observed. In addition, they found that A1 feeding relative to A2 feeding significantly increased the colonic activity of the inflammatory marker myeloperoxidase by ~ 65%. Unlike the degradation of GLP, GIP & co, this effect which was significantly more pronounced (+207%) in a previous study by Haq et al. (2013), where only A1, in the absence of other molecules from milk was administered, was directly mediated by the activation of the opioid receptors in the gut.

The scientists from the National Dairy Research Institute in India were also able to show that the intestinal interleukin-4 and immunoglobulin E levels as well as the leukocyte infiltration increased with A1 compared with A2 feeding.
Why does all this matter? In view of the accumulating evidence that intestinal inflammation disturbs not just the colonic microbiota composition and enhances pathogen growth, but has negative downstream effects on one's overall metabolic health, any changes in intestinal markers of inflammation could be potentially health relevant.
BCM-7 has also been reported to alter human intestinal lymphocyte proliferation and promote mucus secretion via MUC5AC mu-opioid receptor activation (Trompette. 2003; Zoghbi. 2006). Now these in vitro studies would be more or less irrelevant, if
"[...] bovine BCM-7 [had not] been detected in the jejunal effluents in humans fed 30 g of casein in amounts compatible with a biological action, which confirms the identification ~30 years earlier of immunoreactive BCM-7 materials in the aspirated small intestinal contents of healthy male adults following milk intake." (Ho. 2014)
Bovine immunoreactive BCM-7 has also been detected in the blood of human infants fed cows’ milkbased infant formula and some Internet sources claim that they are partly responsible for the increased allergy-risk in formula-fed babies. Still, scientists like A.S. Truswell believe that the in-vitro evidence is insufficient and highlight that they "have not yet seen clear evidence that this peptide is released and active in humans in vivo," (Truswell. 2006) citing Svedberget al. (1985) as an example, who found peptides in the human small intestine after the ingestion of 1l of bovine milk that reacted immunologically as if beta-casomorphin 7 but it did not show opioid activity or behave  chromatographically as authentic beta-casomorphin-7.

With its opiod-receptor interactions there is still a plausible mechanism that could explain some, but not all of the often cited ill health effects. A human study which assessed whether A1 relative to A2 beta-casein-containing milk imparts different gastrointestinal effects in human adults, however has not been conducted before.

It's time for real human data, now!

It was thus about time for Ho et al. to approach this issue by investigating the the gastrointestinal effects of dietary A1 versus A2 beta-casein-containing milk in adults using subjective and objective measures of gastrointestinal performance.

In an 8-week cross-over study, 12 men and 29 women (19–68 years) from Perth, Western Australia, were randomly assigned to one of two groups for 2 weeks, following a 2-week dairy washout in which rice milk substituted dairy milk (A1) milk containing beta-casein of A1 type (n= 21); or (A2) milkcontaining beta-casein of A2 type (n= 20). Exclusion criteria were as follows: (1) milk allergy; (2) diagnosed lactose intolerance; (3) pregnancy/ lactation; (4) cardiovascular events in the last 6 months; (5) opioid consumption; (6) antibiotic treatment in the previous 8 weeks; and (7) immunosuppressive medication or anti-inflammatory drugs in the 4 weeks before screening. Before crossing over to part II of the study, the participants underwent a second 2-week dairy.
One thing that may be relevant for the interpretation of the study results is the fact that a subgroup (n= 10) had self-reported intolerance to commercial milk - a problem that could be related to the comparatively high A1 beta-casein content of milk. The fact that three participants withdrew from the study during the A1, but only one of the patients withdrew during the A2 phase would further support the notion that A1 beta casein does - at least - increase the risk of milk intolerance and gastroinstestinal overreactions.
During the 2-week A1 and A2 beta-casein interventions, participants were instructed to consume 750 ml/day of their allocated milk (containing ~ 7.5 g of either A1 or A2 beta-casein) over the day and to avoid all other dairy products. The A1 and A2 milk were both standardised to the following nutrition
profile per 100 ml: energy 189 kJ, total protein 3.1 g, total fat 2.5 g and lactose 5.2 g; no other known differences existed.
"Proteome Analysis Facility, Macquarie University, Sydney, NSW, Australia) of the A1 and A2 milk showed that the A1-type beta-casein proportion of total beta-casein was 499% in the A1 milk and⩽0.5% in the A2 milk."
The milk was processed and packed in identical 1-l UHT plain packages (blinding participants and the investigator to each milk intervention) by Pactum Australia Pty Limited, Taren Point, NSW, Australia, to ensure successful blinding.

The assessments, the scientists did included anthropometry, diet and physical activity measurements, a test for markers of inflammation in the gut, and subjective recording of gastrointestinal symptoms. The tummy aches, flatulence, stool consistency, etc. as well as the general food intake and compliance, i.e. "did I ingest my milk, or didn't I" were recorded in daily logs. An analysis of these logs revealed that the
[...m]ean compliance with the A1 and A2 diets was 96.2% (±5.3) and 96.4% (±6.6), respectively. Greater than 100% compliance stems from some participants consuming extra study milk in tea/coffee/food." (Ho. 2014)
Significant between group differences for milk, energy, fibre or calcium intakes during the intervention were not detected. The latter could not be said for the quality of the stools: As you can see in Table 1 there were significant differences between the stool quality during the A1 and A2 phase of the study.
Table 1: . Bristol Stool Scale analyses of stool consistency (mean±s.e.m. | Ho. 2014)
Interestingly, a subgroup analysis revealed that these differences were significant only in women and the previously mentioned subgroup of initially 10 subjects who claimed that they were milk intolerant.
There is one interesting difference between A1 first vs. A1 second consumption. In contrast to those who switched right onto the A1 diet after the preceding "no-milk" phase, the scientists observed a significant increase in bloating and flatus. For subjects who consumed the "bad" A1 caseins after getting used to "milk" in an initial A2-only phase, on the other hand, there was no such effect. At least for me, this supports the notion that regular milk, which contains both caseins, cannot be generally bad for everyone (check out the figure in the bottom line, as well).
Against that background, it's a at least surprising that the values of gastrointestinal discomfort were numerically higher on the A1 diet, but not significantly elevated - even for the eight remaining milk intolerant individuals, for whom the mean A1 values were considerably higher than A2 values for bloating (61% higher), abdominal pain (38% higher) and voiding difficulty (83% higher), statistical significance was not detectable due to the the small participant numbers in the selfidentified milk-intolerant group.

Among the correlates of the gastrointestinal symptoms the scientists evaluated, only the absence of the A1-exclusive correlation between loose stools and abdominal pain appears worth mentioning. Loose stools, which were less frequent in the A2 group, could thus be a first indicator for what I would like to call A1 intolerance. Whether this is a direct result of the previously discussed opiod-receptor interaction is yet uncertain. As Ho et al. point out, the loose stools could also be the result of
"[...] greater opportunities for food fermentation and hence digestive discomfort within the gastrointestinal system." (Ho. 2014)
This effect would that occur in response to the initial increase in gastric transit time due to A1 consumption, not as a direct consequence of opiod-receptor interactions. Assuming that the "fermentation hypothesis" is correct, the difference between "milk tolerant" and "milk intolerant" subjects could eventually come back to something as simple as having the "wrong" gut bacteria. Corresponding evidence that probiotic supplements can sooth the pro-inflammatory reaction in milk intolerant subjects comes from a study by Pelto et al. who observed that probiotic bacteria down-regulate the milk-induced inflammatory response in milk-hypersensitive subjects but have an immunostimulatory effect in healthy subjects (Pelto .1998).
Overview of a handful of studies showing reductions not increases in diabetes, as you would expect them if the GLP-1 reduction in response to the tons of "bad" A1 casein in regular dairy would be the significant health risk some Internet resources claim it was. Accordingly, there is at the moment no reason for milk tolerant individuals to avoid "regular" dairy.
But let's stop speculating... I guess, all we can say in the case against A1 now is that there is evidence which suggests that people with existing milk intolerances may have to be careful with respect to the ingestion of A1 containing foods. For everyone else, the evidence that it would harm their health is simply not there (yet?).

The idea that the degradation of BMC-7 will induce collateral damage in form of a reduction of beneficial incretins such as GLP-1 would still suggest that it's worth keeping an eye on the research, even if the contemporary available evidence does not suggest that consuming milk and dairy products would have a negative effect on body weight and glucose tolerance as you would expect to see it in response to the GLP-1 degrading effects.

I mean, look a the reductions in diabetes risk in dairy lovers in the seven studies I used to build the graphical overview on the right. With all that "bad" A1 casein in regular dairy the negative effects should show on a population level, shouldn't they? You think differently, let me know on Facebook!
  • Barnett MPG, McNabb WC, Roy NC, Woodford K, Clarke AJ. Dietary A1β-casein affects gastrointestinal transit time, dipeptidyl peptidase-4 activity, and inflammatory status relative to A2β-casein in Wistar rats. Int J Food Sci Nutr 2014; e-pub ahead of print 20 March 2014; doi:10.3109/09637486.2014.898260 
  • Choi, Hyon K., et al. "Dairy consumption and risk of type 2 diabetes mellitus in men: a prospective study." Archives of internal medicine 165.9 (2005): 997-1003.
  • Choi, Hyon K., et al. "Dairy consumption and risk of type 2 diabetes mellitus in men: a prospective study." Archives of internal medicine 165.9 (2005): 997-1003.
  • Cielinkska A, Kostyra EB, Kostyra H, Olenski K, Fiedorowicz E, Kaminski SA. Milk from cows of different beta-casein genotypes as a source of beta-casomorphin-7. Int J Food Sci Nutr 2012;63:426–20.
  • De Noni I. Release of b-casomorphins 5 and 7 during simulated gastro-intestinal digestion of bovine b-casein variants and milk-based infant formulas.Food Chem 2008;110: 897–903.
    Jinsmaa Y, Yoshikawa M. Enzymatic release of neocasomorphin and beta casomorphin from bovine beta-casein.Peptides1999;20: 957–962. 
  • Elwood, Peter C., Janet E. Pickering, and Ann M. Fehily. "Milk and dairy consumption, diabetes and the metabolic syndrome: the Caerphilly prospective study." Journal of epidemiology and community health 61.8 (2007): 695-698.
  • Elwood, Peter C., et al. "The survival advantage of milk and dairy consumption: an overview of evidence from cohort studies of vascular diseases, diabetes and cancer." Journal of the American College of Nutrition 27.6 (2008): 723S-734S.
  • Grantham, Narelle M., et al. "The association between dairy food intake and the incidence of diabetes in Australia: the Australian Diabetes Obesity and Lifestyle Study (AusDiab)." Public health nutrition 16.02 (2013): 339-345.
  • Haq MR, Kapila R, Sharma R, Saliganti V, Kapila S. Comparative evaluation of cow β-casein variants (A1/A2) consumption on Th2-mediated inflammatory response in mouse gut. Eur J Nutr2013;53: 1039–1049. 
  • Ho, S., et al. "Comparative effects of A1 versus A2 beta-casein on gastrointestinal measures: a blinded randomised cross-over pilot study." European journal of clinical nutrition 68.9 (2014): 994-1000.
  • Liu, Simin, et al. "A prospective study of dairy intake and the risk of type 2 diabetes in women." Diabetes Care 29.7 (2006): 1579-1584.
  • Pelto, L., et al. "Probiotic bacteria down-regulate the milk-induced inflammatory response in milk-hypersensitive subjects but have an immunostimulatory effect in healthy subjects." Clinical and Experimental Allergy 28.12 (1998): 1474-1479.
  • Schmelzer CE, Schops R, Reynell L, Ulbrich-Hofmann R, Neubert RH, Raith K. Peptic digestion of beta-casein. Time course and fate of possible bioactive peptides. J Chromatogr A 2007;1166:108–115. 
  • Svedberg J, de Haas J, Liemenstoff G, Paul P, Teschemacher H (1985). Demonstration of B-casomorphin immunoreactive materials inIn Vitrodigests of bovine milk and in small intestine contents after bovine milk ingestion in adult humans.Peptides6, 825–830.
  • Tong, X., et al. "Dairy consumption and risk of type 2 diabetes mellitus: a meta-analysis of cohort studies." European journal of clinical nutrition 65.9 (2011): 1027-1031.
  • Trompette A, Claustre J, Caillon F, Jourdan G, Chayvialle JA, Plaisancie P. Milk bioactive peptides and beta-casomorphins induce mucus release in rat jejunum. J Nutr 2003;133: 3499–3503 
  • Truswell, A. S. "Reply: The A2 milk case: a critical review." European Journal of Clinical Nutrition 60.7 (2006): 924-925.
  • Zoghbi S, Trompette A, Claustre J, El Homsi M, Garzon J, Jourdan G et al. beta-Casomorphin-7 regulates the secretion and expression of gastrointestinal mucins through a mu-opioid pathway.Am J Physiol Gastrointest Liver Physiol 2006; 290: G1105–G1113
Disclaimer:The information provided on this website is for informational purposes only. It is by no means intended as professional medical advice. Do not use any of the agents or freely available dietary supplements mentioned on this website without further consultation with your medical practitioner.