Scandinavian/Celt. Low carb tolerance, also am now sure I am celiac after stubbornly reintroducing very occasional wheat and soy (mostly in the form of pancake/baking mixes) in 06 and again in 09. Both times led to return of baaaaaad multiple system symptoms. I will never know now as I will never eat grains again, and thus cannot be tested.
Have no idea re: parent/grandparent tolerance as I am an adoptee. However, info I have been able to get included a statement by my birthmother @ age 24yyears that paternal grandparents had both suffered from cancer, but otherwise, esepcially her family was "disgustingly healthy."
I don't have to eat zc or vlc on a daily basis, but did have to go what I know was quite low to lose the 90+lbs originally. I have never counted anything, so can only estimate. The other night I estimated carbs for the first time. I took in about 70 that day I think. I do well doing "change-it-up." This means I change my eating cyclically like crazy - very high fat today, much lower tomorrow. ZC x3 days, then very heavy on the veggies and lesser meat/fish/fowl...if I want to do a carb spike day, it is through nuts, primarily. I am suspicious also that too starchy carb is implicated in some of my autoimmune stuff, whihc I want to deep GONE!
Sugar is NOT my friend. Period. Fruit consumption is permanetly limited to only low gly/low load berries etc and they are infrequent. Do very well with PILES of non starcy carb vegetables. My plate often looks vegetarian - just all low carb veggies + the protein/fat.