> In the many conversations I've had about processed foods, people never seem to be talking about things like milk, yogurt, or cheese, all of which undergo _heavy_ processing.

The faddish 'paleo/caveman diet' definitely says you shouldn't eat these, and I think that's the poster boy for the unprocessed diet. But it also depends on your genetics, if you're from a lineage that has no issue with lactose then it's probably fine. They are very calorie dense though if weight loss/maintenance is a goal.