42 lbs. Online research will help you improve your weight loss.
How much weight will a 298 pound morbidly obese person lose if they eat 1,000 calories a day and limited carbs?
There are books that have charts based on age, activity level, calorie deficits and other pertinent factors.
God to your local library and get help from a reference librarian.
Your question contains far to little information for a useful answer.
1st of all, it depends on how long you do that. But it mostly depends on how good/bad your metabolism & genetics are. If your genetics are bad, it doesn't matter what you do (healthy or not) & for how long. You'll gain more weight faster as you get older.
2nd of all, eat less than 1,000 calories a diet & as less carbs/calories as you can. & exercise as much as you can.
Too many variables pertaining to an individual to say exactly.
It is not an exact science.
I'm thinking the better question would be .. Just how healthy can a person get if they followed a healthy diet? Still impossible to answer...but you get the picture.