VeryGnawty
"is fasting really just starving yourself?"
The difference between fasting and starving yourself is state of mind. In Zen Buddhism, they say that there are some who go for a very long time without eating rice, yet they are never hungry. Yet there are others who eat all the day long, and are never satisfied.
Thus, starving is just a state of mind.
"does your body really even need all the food i put into it?"
No.
"can i fast for 15-40 days my first ever fast?"
Yes.
But the question isn't whether you can fast for forty days. The real question is, SHOULD you fast for forty days. The answer to this questions, depends on many factors. For most people, the answer to that question is: no.