Can you Throw up from not eating?
It is not normal to throw up after eating, and one should definitely not want to throw up purposively after eating. The nutrition in food usually needs at least 12-24 hours to be fully digested. If you want to intentionally throw up after eating, you likely have an eating disorder or a digestive disorder.
How long it takes a cat to throw up after eating grass can vary quite a bit, depending on things such as how much grass the cat ate and what else was in its stomach. In general, a cat will throw up anywhere from almost immediately to 5 or 10 minutes after eating grass, though that don't always throw up at all.