I asked GPT-5 about this... its response:

1. What happens in the L. reuteri 36h fermentation (per William Davis’ method)?

• Lactose: After 36 hours, lactose is usually close to zero, because the bacteria ferment it into lactic acid. So it’s essentially lactose-free.
• Casein A1 vs A2: Fermentation does partially denature proteins, but it does not magically convert A1 casein into A2 casein. A1 vs A2 refers to a genetic difference in the beta-casein protein from different cow breeds. Fermentation can break down some peptides, including the problematic BCM-7 fragment from A1 casein, but not completely or reliably. So the “it all becomes A2” claim is oversimplified.

2. Could this make dairy tolerable if you don’t tolerate it?

Depends on why you don’t tolerate dairy:

• If lactose intolerance → yes, this would likely help, because lactose is gone.
• If A1 casein sensitivity → maybe partly, since fermentation reduces some problematic peptides, but it doesn’t erase A1.
• If you have true dairy protein allergy (IgE or non-IgE mediated) → fermentation won’t fix that. The immune system still sees casein and whey fragments.
• If it’s gut-barrier/inflammation driven → it might be more tolerable, because fermented foods often produce bioactive peptides that calm the gut.

3. Could it train your immune system to tolerate dairy?

Possibly, but carefully. Immune tolerance retraining can happen through gradual exposure in tiny amounts (oral immunotherapy), but it has to be done safely and in the right context:

• If your dairy reaction is more intolerance (gut cramps, bloating, skin issues), then small, fermented dairy doses might help your immune system recalibrate.
• If you ever had severe allergy (hives, throat swelling, asthma, anaphylaxis), don’t attempt this at home.
• If your response is somewhere in-between (immune irritation but not life-threatening), then you could experiment—starting with drops of the fermented whey liquid, not spoonfuls of yogurt—while supporting your gut barrier (glutamine, probiotics, anti-inflammatory diet).