My younger son also goes through periods when he seems to exist on air (we joke that he photosynthesises), so I sympathise. Even when he eats, he generally has days when he will only eat carbs and days when he will only eat protein - rarely both on the same day, and almost never both at the same meal. Obviously if there is a developing medical problem beyond the not-eating itself, it will need to be dealt with in some way, and that's beyond my expertise. All I can say is that whatever the solution is, it needs to be one where food doesn't give Alex power over you, because that poisons the parental relationship and the child's relationship with food. (I know you know that, but sometimes it helps for people to say these things anyway.) A book that I've found tremendously helpful is Preventing Childhood Eating Problems by Jane Hirschmann and Lela Zaphiropoulos. It has chapters corresponding to different age groups. I didn't read the ones for the very youngest ages too closely, because my kids were at school by the time I got it, but it might be worth a look.