My wife has only recently been able to go an entire day without eating, under keto/low carb. We’ve been doing keto/low carb, but she still had to eat three meals a day, or she got headaches. Her headaches from lack of eating had always occurred, since she was a child.
It’s highly likely that the problem is dehydration combined with low sodium/potassium/magnesium.
Keto/low carb diets are both naturally dehydrating and salts depleting. Especially when you are eating whole foods rather than high sodium packaged convenience foods.
I generally put a few grains of pink rock salt under my tongue throughout the course of my fasting periods. I still struggle with drinking enough water and remembering to salt my food, since I was trained out of that by standard medical advice. Low sodium, low fat dietary advice was killing me and is still killing others.
But I am off all meds except my BP med which has been reduced to a half tab of a 25mg tab as I continue to lose weight. I hope to be off of it by spring.