Update: I have lost about half a kilo in a week. So my weight now fluctuates between 49.5-56.5. Anyone know how to stop it from moving around so much?
Most people I talk to put weight down to a number, a dress size, a particular appearance. For most women, 60 is the magic number, as in 60kg. Under 60, and you're pretty trim. That's the main idea.
But it doesn't always work like that. I'm a good four or five kilos under 60, and I'm not really the trimmest person to walk the planet. In fact, I'm pretty sure if I ever hit 60 I'd be one chunky monkey. So it does vary, a lot. For some women (like me), 50 or 55 is pretty much the max. Other women can hit 60, 70 or even 80 and still be healthy.
You can't tell how healthy you are by your appearance. Fat cells are decided genetically - as in, you can't control it. You'll always have a minimum weight that you can't avoid without becoming seriously ill. You gain or lose weight by filling these fat cells with fat, but they're always there, and they always have a little fat in them. It's healthy and perfectly normal. This is also why some people find it hard to gain weight. Fat, and acceptable levels of fat, is also dictated by your racial and ethnic background - for example, if you're white with a medium build you can probably get away with a few more pounds than someone who's the same height but Asian with a slightly smaller build. Conversely, some races are just naturally plump to endure conditions in native lands (i.e. Eskimos).
Fat is also only one factor in general wellness. You can be fit and active and still be 60kg with generous love handles, but you'll be miles healthier than a skinny stick who smokes and eats burgers all day. The problem is that in this day and age we associate general health far too much with the number our scales churn out, and a lot of people think they're fine because they're thin when in fact some are more unhealthy than people who are a trifle overweight.
You can't always tell if you're the correct weight by appearance, either. Fat in different places mean different things, for example, fat in the breast, buttocks and thighs are actually healthy and essential for female fertility, but fat in the stomach is linked to diabetes and heart disease.
Stretch marks can be caused by weight gain, but are more often caused by pregnancy or the sudden growth spurts in adolescence. This is why babies have such lovely fat rolls, because this is when human beings do the most growing - if babies were as slender as adults they'd have stretch marks all over.
BMI calculators are also pretty flukey, because they don't take into account ethnicity, metabolism, age etc - Arnold Schwarzenegger would actually be chronically obese according to his BMI (he probably is now, but I was talking about his Terminator days). I have a pretty low BMI, but it doesn't mean much - a BMI calculator is useful in ensuring that your goal weight, if you're trying to lose weight, is healthy. I would like to be about 50-53kg, which is still well within the healthy BMI range. That's pretty much the only time I'm going to use the BMI calculator, because according to it I could go up to 63kg without being 'fat'! I'm 'fat' already!
My advice about getting fit is not to stress too much about it. Focus on being fit and healthy, not the abuse your scales give you. A little bit of icecream won't kill you, and no matter what, you're never going to look like Miranda Kerr.
I'm always going to be a big girl. But big girls still have to climb a few flights of stairs without having heart attacks. It's part of life.