"Why is my appetite changing so much?"
I will go days where I don't want to eat at all. And then I will have like three days in a row where all I want to do is just keep eating and eating and eating. Why does my appetite keep going up and down?
This is an interesting question and symptom that is very vague and only prompts many more questions. Things like appetite are affected by so many other factors, that it is nearly impossible to answer them definitively in the absence of more information, and usually a physical examination. Many social factors go into eating, and it could be that your appetite varies based on the social setting or your mood at the time that you are ready to eat.
While it is important to get enough energy to fuel your body and keep you healthy, the binge eating that you seem to be describing is a behavior that is not entirely healthy. Speaking to your doctor is an appropriate step to make sure that there is not something more serious, such as variations in your hormones or other factors, that are contributing to your problem. Other questions, involving things like your bowel habits, will also need to be addressed to fully understand why you are experiencing this shifts in your appetite, and whether or not it is contributing to your health. Please speak to your doctor, and maintain healthy eating habits both before and after the visit to make sure you remain well.
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