newcastle is an extreme diet, based on starvation. it's always good not only to consult your doctor, but do it under some medical supervision. I won't go for it if I was you, it's too early an extreme, collect more info.
keto is not so hard, but check about the side effects in the first too weeks, to be prepared. It's also required to get plenty of water, magnezium, potassium and salt during this period of adaptation. Consult a doctor if you have other preconditions, to make sure they don't interfere. Otherwise, look for as much info as you can before starting it.
I'm on my second week of Keto and I still have side effects, but I didn't need to check with my doctor first.