Fasting is a good way to achieve that.

But as far as donating goes, there may be a day you might be the recipient of much needed blood donations.

Had a lady need 12 bags of blood after almost exsanguinating following a really complicated delivery (both survived). She never gave blood before due to fear of needles, but now is a regular blood donor because of the importance of it. She told me to not wait and just start giving.