Ever considered serotonin?
The production of serotonin begins with the essential amino acid Tryptophan (essential, meaning it can’t be produced by the body and is only absorbed by the body from the foods we eat). Tryptophan is then converted via hydroxylation to form 5-hydroxytryptophan and then decarboxylation to form serotonin.
During a crash diet of any significant length of time I would imagine serotonin would be impacted heavily due to this. Recovery time from this I would have no idea. Though people take ssri’s for a reason, increasing serotonin is not easy. A serious hit to your serotonin could have serious long term consequences.
Serotonin has a myriad of functions in the body, including gut health, mental stability, sexual function, sleep and body temperature just to name a few.
I’m not sure how this would corelate to npp or Deca use although from what I understand nandrolone can have serious impacts on neurotransmitters so this may explain it.
Just food for thought. I was doing a bit of research on serotonin and thought of this thread and the crash diet thread with regards to the serious impacts on sexual function. I could be completely off with the above although its worth a thought.