Maybe you’ve seen it as a guideline for calorie restrictive diets, maybe you’ve heard it’s the bare minimum of calories you should consume in one day, but, have you ever wondered where this magic number comes from? Well, in my time working as a nutritionist I investigated the mystique of the 1,200 calorie threshold.
It comes from the theory that if you let your calorie consumption dip too low your metabolism will go into ’starvation mode’, meaning it will slow down considerably. This causes your weight loss to plateau if you maintain the same energy intake, or causes you to put fat on if you increase your calorie intake again (for a consistent period, and by a considerable amount). But then, that begs the question of how anorexics manage to keep getting so skinny consuming usually a maximum of 1,000 calories a day, if that. What’s the deal?
Well, the minimum guideline comes from what is assumed to be your Basal Metabolic Rate (BMR). Namely, the amount of calories your body would burn if you did nothing all day. And I do mean nothing. You’d be bed ridden. That’s not to say that 1,200 calories is what everyone would burn at rest, but it’s the standard estimate used for an average aged woman of average fitness or average size. It can varies for everyone — by quite a bit too! My BMR, for example, is about 1,400 calories per day, and that’s mainly because I’m fairly young (28). That’s a lot more than 1,200!! So, in essence, the theory is that if you let your average calorie consumption go below your personal BMR, you risk entering your body’s metabolic ’starvation mode’. Plus you’d just be really really cranky and tired.
So what about those scrawny anorexics? Well, at first their bodies did resist weight loss, provided they jumped right into extreme deprivation from normal food intake. But, in general, anorexics started as regular dieters and got worse (more restrictive) over time. Their bodies have not only burned their fat mass off for fuel, but their muscle mass as well. Some muscle loss is inevitable when losing weight. And that really is ok and unavoidable. Your body simply does not need as much muscle as it used to to lug around your weight as you get lighter. But it’s when the body is truly starving (ie// not getting enough calories to meet your basic needs –your BMR level), that it starts to deplete muscle mass alarmingly because it takes the most energy to maintain, but generally you will lose fat first. Anorexics die of general malnutrition and from their bodies needing to resort to using muscle sources –like your heart– for fuel.
The bottom line is this: don’t let your calorie intake dip below your BMR. There are equations to give you an estimate of what your BMR is and they should factor in your age, sex, and weight. 1,200 is not the BMR for everyone. Your BMR will be higher than that if you are: tall, possess a lot of lean muscle mass (ie// an athelete), young, male, or are just genetically blessed with a faster metabolism (although, this generally doesn’t make too much of a difference — usually only 50-75 calories/day).
Estimate Your BMR: http://en.wikipedia.org/wiki/Metabolic_rate#BMR_estimation_formulas