First off, you should clear this proposed fast with your Spiritual Director (if you have one), or with your local Priest. You need to make sure your motives for this fast do not include spiritual pride.
Next, you should have a physical checkup from your Physician, explaining what you are planning to do, and asking for permission and guidelines for doing it. And if the Physician says “no”, obey. God loves obediance.
As always, these OPINIONS have not been endorsed by my three cats, who regard fasting as something only dog lovers could invent:rolleyes: