If you only eat 400 calories a day how much weight will you lose?

You will lose A TON of weight the first few months.. but honestly, if you are contemplating whether or not you should eat 400 calories a day, I am giving you cold hard advice to NOT do it. I am a recovering anorexic who would eat around 500 calories daily, and at month number 3, I realized I had a problem when my period didn't come, I felt tired ALL the time, I began falling into depression, and all I could think about was food and my appearance. Every living thing NEEDS food as it is fuel for the body, and most doctors recommend to not eat under 1200 calories because per day, a person usually burns as little as 1200 calories just by living. 400 calories is less than 1/3rd of what you should eat daily and if your body isn't getting the fuel or nutrients it needs, it will go into starvation mode, and once you're ready to eat as much as you did before weight loss, you will most likely end up gaining more weight than initially. Anywho, as for your question.. You'd probably lose around 2-3 pounds per week.. but like I said.. I strongly suggest you not go down that dangerous path.