Ruth, I agree with a pp about your ethnic background & area giving more details than just general stuff. For example, I'm Greek, but both my parents come from areas in Greece that are not hospitable to cattle. So any milk my ancestors may have ingested would have been goats milk. And I tolerate goats milk a lot better than cows. However, dairy tolerance is hit or miss throughout the mediteranean area, and I happen to be one of the misses. I'm sure if you were to tell us your ethnic background & what parts your ancestors came from (ex. Southern Germany, vs. Northern) and we can narrow it down for you.

Momily, I don't think you need to make different meals necessarily. Just look at what your son's ancestors would have eaten. If dairy was non-existant, it's safe to say he shouldn't focus on dairy products that much. Otherwise, I think preparing any food traditionally is beneficial to everyone, regardless of ethnicity. Eating corn prepared traditionally is good for me, even though my ancestors NEVER ate it until, well, my mom came here in the 80s, lol. Now, if I were to show a sensitivity to a certain food, that's another story.
That said, people prone to digestive issues probably need lots of fermented foods in their diet to strengthen that area. Type 2 diabetes probably needs to keep vigilant on the amount & type of carbs eaten (never refined, only properly prepared grains sparingly, etc). Etc, etc. All of these issues are really a matter of rebalancing a general traditional foods diet to include more of one (or more) items instead of others. I wouldn't say that they are due to not eating 'true' to ancestral type. Ok, that didn't make sense, lol. In other words all of these issues are resolved by eating more of certain foods, rather than only eating what one's ancestors ate.
Ami
Ami