Is this why in the course of human history, religions eventually come to feel the need for "reform"?

Seriously though, and unrelated, I find it interesting that in my religion Hinduism too, religious fasting often centers around not eating grains that day with no restriction on fruits and vegetables.

[speculation]
Possibly the "agricultural revolution" left diets overly dependent on grains and these customs are ritualized reminders of the ancient attempts to restore balance away from grains. Perhaps, today's "low-carb" diets represent the latest attempt in the same direction.
[/speculation]