There are two reasons that there's a lower limit to your calorie range:
1) to make sure you get enough nutrients. At 1400-ish, if you do some planning and avoid empty calories, you can meet your nutritional requirements. It's pretty impossible to do that with less than 1200 calories, but 1400+ gives you room for error. Being larger doesn't mean you need a whole lot more calcium or fiber, for example.
2) to let you lose a reasonable amount of weight without unnecessary suffering. At 300 pounds, you're going to lose weight as long as you stay below about 2000. You'll lose faster at 1500 or so, but only if it's comfortable. If you're hungry or just feel bad, the natural human response is to quit doing what makes you feel bad, and that's why people "cheat" or "quit" diets. The low end of your range is the lowest level that dietitians think some people might be able to stand. It's not necessarily right for you. You might feel sick or hungry if you cut back that far-- and if you do, it is perfectly all right to eat more.
So, as others have said, don't go that low if you don't want to. You're in this for the long haul, and you're far more likely to get where you're going if you're comfortable at the start.
| current weight: 132.0