My husband's side of the family - everyone is skinny. They are not high carb eaters. They don't like sweets (desserts that are brought over do not get eaten) and they crave salt and vinegar type snacks. If anyone is snacking in the house it will likely be mixed nuts or pickled hot peppers. My husband started to eat high carb when we got married and within about 6 months started having indigestion problems. I knew immediately what it was and offered him more of "his" foods (before I was low carbing).
I was brought up on high carb and my body tolerated it until my mid-teens. I started to realize at that early age that I was having indigestion, constipation, etc but didn't know why. I continued to ignore my body and became VERY ill in my late 20's with a candida infection.
I believe our metabolisms are all "essentially" the same. However, if you start to low carb at age 30 or 40, your body is in for a HUGE change (as was my husband's body going from relatively low carb to high carb).
I believe low carb is the way we are supposed to eat.
Trying to be a vegetarian almost killed me (no touche' intended but it is the truth).