"Is it healthy to eat 1000 calories a day?"
No it is NOT healthy tom eat one thousand calories a day, and that's regardless of age or gender. Anyone that's eating that few of calories a a day, is taking unneeded risks, with their health. It can also be a sign of an eating disorder, and most commonly that's anorexia. One major issue with such a low caloric intake, is in meeting the base RDA of the more than fourty essential nutrients, at both the macro, and micro levels. While it can be done, it's very difficult to do,even some of the most knowledgeable in diet and nutrition would be hard pressed to meet on a continual basis all of the essential nutrients, that also includes registered dietitians. The base amount for a healthy diet, ranges from about fifteen hundred to two thousand calories a day, and maybe more depending on how active you, or anyone else is.