<This is something of a running fight. True of some modern
animals like deer, but not all. But was it true of the
extinct animals? From cave
art to frozen mammoths in the arctic we know that paleo
mega-fauna carried huge fat deposits.>

Would it not make sense that we ate the large, fat,  slow moving, easier to
kill animals that  were in abundance prior to 10,000 yrs. ago.
I  doubt we would have past them by to chase a deer or skinny, lightning
fast gazelle.  If this is true then we would scarcely have had sufficient
time to
adapt to this very low fat food(rabbit starvation), just as we have been
unable to adapt to grains(name your problem).

I believe we are best suited to the fatty meats and as the ice age ended we
were forced to eat lean meats and grains to survive.
In time we may possibly adapt to both.

Jeff