Different people learn easier with different methods, for example some will remember the information easier by writing the information with a pen and paper, some will learn easier by saying what they're reading, some learn easier by being read to.
Although repetition helps a lot, if you're learning in a way that you have difficulty with will make you learn much slower.
Eggs and fish in general are good for the brain.
The human brain usually remembers the beginning and the end of a long session, taking a few minutes every 15 minutes or so to rest and reflect on what you've studied will help a lot.
Lack of blood flowing to the brain won't help, if you get fatigued you can try some breathing exercises to help your brain acquire more oxygen (moving around or stretching every so often helps as well).
Meditation for awareness:
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