When I had anorexia, I went a steady 6 months with less than 150 calories a day. Worst 6 months of my life, it was absolute hell. Basically an apple and half a slice of bread for the whole day. Now I don't count calories, but I'm guessing I'm somewhere between 2000-2500 a day, and I've never felt better. I changed my diet to low fat high carb vegetarian, and since then I've actually lost weight. I'm visibly thinner than when I ate about 1800 with high fat low carb vegetarian, so the source also truly makes a difference in my experience.