In 'Milk Proteins: The Good and the Bad' Dr. Phil Maffetone discusses dairy, and specifically milk proteins casein and whey.
Most of the protein in milk is casein, but not all casein is the same. A1-casein is the bad type you want to avoid, while A2-casein is the good one.
Most dairy sold in supermarkets contains mostly A1-casein. However milk from animals like goat, sheep, buffalo and Brown Swiss cows contains A2-casein.
If you occasionally like to eat a little good quality cheese, choose cheese from milk of
- goat (Chevre, feta)
- sheep (Pecorino, Roquefort)
- buffalo (Mozzarella di Bufala)
- Brown Swiss cows (cheeses of Switzerland).
If you can tolerate some dairy, it's always a good idea to hunt for the very best products, like grassfed organic butter. Yes it is more expensive, but think of it as an investment in your health and fitness.