Not to discredit your friend's or Burtlancast's experience, Lindsay, but for me personally, I saw no difference between A2 certified 100% grass-fed milk from Guernseys and Devonshire heritage breeds, goat dairy and plain old Organic Valley or Stonyfield milk. In fact, the farmer I get my A2 milk from isn't convinced that there is validity to the A2 beta casein claims, but he went ahead and had his cows tested anyway for his customers. The thing that raises a red flag for him and I is that, at the time (I'm not sure if it's still the case), farmer's milk could only be licensed as being A2 milk if the cows were tested through the same company that claimed A1 to be an issue, the A2 Milk Company. Here's a quote:
"While the company marketing A2 milk claims that milk containing A1 proteins are harmful, there is no scientific evidence that A2 milk has benefits over normal milk.
A1 and A2 beta-casein are genetic variants of the beta-casein milk protein that differ by one amino acid. The A1 beta-casein type is the most common type found in cow's milk in Europe (excluding France), the USA, Australia and New Zealand. A genetic test, developed by the A2 Milk Company, determines whether a cow produces the A2 or A1 type protein in its milk. The test allows the A2 Milk Company to give licenses to milk producers once these producers prove their cows produce only A2 beta-casein protein in their milk, to the exclusion of the A1 beta-casein protein type."
Here's what is said about the A1 mutation:
"All proteins are long chains of amino acids. Beta casein is a chain 229 amino acids in length. Cows who produce this protein in their milk with a proline at number 67 are called A2 cows, and are the older breeds of cows (e.g. Jerseys, Asian and African cows). But some 5,000 years ago, a mutation occurred in this proline amino acid, converting it to histidine. Cows that have this mutated beta casein are called A1 cows, and include breeds like Holstein."
So that would mean 5,000 years of dairy intolerances for anyone drinking milk from Holsteins or other A1 cows. When I was a little girl in the 80s to early 90s, there were no buzz words like A1/A2 casein, grass-fed, raw ect. and it was rare that a person had a milk allergy. I personally never knew anyone with a dairy allergy.
I'm not sure why your friend has an issue with milk in the US, but what we do know for certain is many of the people on the Ray Peat forum as well as here, are pretty extreme cases in terms of our diet and health history. Many of us found Ray Peat because our health was in the tanker due to restrictive diets like low-carb or fruitarianism ect. so I'm not surprised people are reacting poorly to milk and also many other foods. If you've noticed, people are also complaining about fat gain and fatty livers from the carbs, inflammation from meat and major digestive upset from starches. So perhaps many of the dairy intolerances stem from not only the cows diet, but our own diet history?
One interesting thing I noticed with me is that after taking minocycline for the bacterial infection, I no longer have any skin issues or digestive troubles whatsoever when I have dairy of any kind. How did you handle dairy after the appendectomy and rounds of antibiotics, Lindsay?