Take the climate zone into account!
Diet for living is an intermediate between what is available and the body's reaction.
We are made for quick carbs like fruits, but only when we were living in some tropics full of fruits all year long.
+ animal products.
Other carbs came later on in man's history, to adapt going north, going cold.
Grains are ideal for keeping.
Then also, animal products go up when you go colder.
You cannot make any
profit of what is food for reindeers.
So they eat it, and you eat the
deer.
So, how can you live on forage only appart from little time and your own body reserve?