How do I know how much to eat?

I’m still not fat adapted but currently eating a strict no sugar, no flour diet in a 2-7pm eating window. Generally, I still feel awful – hungry, light-headed, tired. But I know it will pass. (Right?? Tell me it will pass…) My question is – is it possible to eat too little at this stage? I’m noticing that I’m not really hungry for my second meal. Should I eat it anyway?