How many calories must you eat to lose 57 lbs going form 217 to 160?

Answer 1

Unless you do fairly vigorous exercise/work, 1600 cal diet is a maintenance diet and you won't be losing much if anything on it. At around 900 cal you can hope for a half to a whole pound per week.

Answer 2

That depends on how long you want it to take. A reasonable rule of thumb is that your body burns 12 calories per pound of body weight per day by keeping a normal body temperature and continuing to simply be alive, so (your results may vary, each person is different) you can presume that you burn 2604 calories per day by being 98.6 degrees. Add to that any calories you burn by physical activity, let say you burn another 396, for easy, round numbers, by exercising and normal daily activities.

Weight loss occurs when your daily intake of calories is fewer than that 3,000. And how fast you lose depends (in part, it's more complex than this) on how much less your intake is than the 3,000.

Another rule of thumb is that a pound of fat is 3,500 calories.

If your calorie intake was 500 less than your calorie usage (2,500 calories per day in food & drink), it would then take you 7 days to lose one pound of fat. You're trying to burn almost 200,000 calories more than you take in, so use a reasonable diet and exercise plan that you can stick with... it's not doing to happen in a month and you shouldn't expect it to.

The dietary and nutritional nuances are many, and it's much more complex than this. But it's thermodynamically impossible for an overweight but otherwise healthy human being to burn more calories than they consume and not lose weight. Just be patient.