>Even better yet, combine a quarter cup of grains, like rice, with a quarter
>cup of beans (more complete protein), along with a cup or more of some
>vegetable or vegetable combination, plus your protein/meat allotment.
>
>Despite what our ancestors tens of thousands of years ago were capable of
>eating, I  think something like this could prove to be very workable now.

One problem with this logic is pointed out in the NeanderThin book.  A
human body is not like a car engine, that can be made to run on a different
fuel just by making a few adjustments.  It's an extremely complex system
that responds chaotically (I mean that in the mathematical sense, as in
"chaos theory") to changes.

On paper, the grains-plus-beans may look like useful protein, but the
reality is not so simple.  So when in doubt, it's better to play it safe.

Eating "forbidden" foods may not cause immediate sickness, but over a life
time it may trigger cancer or other auto-immune problems.  Eating smaller
amounts would almost certainly reduce this risk.  I myself still "cheat"
with some baked goods, ice cream, etc.; but these are definitely minor
accessories to my diet.  I no longer eat big batches of rice, cereal,
pasta, potatoes, cheese, or beans.