Fasting is not starving oneself. It’s a purposeful denial of sustenance, usually for meditation or for dieting. Starving has more of a negative connotation, as being involuntary because of someone, including yourself as in a protest, withholding food from you or because of a lack of available food.
If you are starving, you don’t have a choice. If you are fasting, you have a choice, and you choose not to.