Demons are egregores; namely, thoughtforms. They guided the ancients, but were literally demonized by the early Christians.
Thoughtforms, once integrated, become homeostatic. By this I mean that the host will prevent modulation to the thoughtform, so long as Maslowian needs are met. When these needs are unmet, the host ejects the thoughtform. This is why revolutions are preceded by famine, disease, and war. Well-fed, safe citizens do not change their minds.
This is also why Jesus stated in Matthew:
And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you. Howbeit this kind goeth not out but by prayer and fasting.
The physiological changes induced by fasting include neurogenesis and increased neuroplasticity. I would imagine that ketogenic diets have similar effects.