Didn't nan huaijin say that he relied on Qigong without eating or drinking? It is to rely on qi to prevent the friction between stomach and stomach. Isn't there a saying that people eat gas?
So I think this depends on enlightenment, that is, on your heart, not on external material methods.
Because besides detoxifying the body, Pigu also has the function of purifying the mind, so I think the key is whether you are savvy and calm down.
Well, the milder way is to eat one bite less every day and then stop eating.
Drink more water, your mood is very important, don't be impatient, don't break the balance of your body, keep your mind at all times, and it's best to do yoga properly (this is good, because yoga also pays attention to fasting)
Taoism means killing three corpse worms, that is, sexual desire, appetite and lust. You should give yourself a psychological hint that you must borrow these three desires during the valley, otherwise there will be no such realm.
Hehe, I wish you success.