So, there are these old weight charts that were developed in the 1950s by insurance companies. There are all sorts of problems with these charts; they failed, for example, to take body type or activity levels into account. As a result, the ranges provided in the tables were unrealistic—and indeed, unhealthy—for large numbers of people, particularly for shorter women or for anyone with a more athletic build. One of the most influential of these charts was the 1959 chart developed by Metropolitan Life. Met Life has since revised those charts, but unfortunately, many doctors and health organizations continue to use the 1959 charts as a baseline.

Another formula often used—and I don't know who came up with this idea, but it's worse—is that women should calculate their ideal weight by allowing 100 pounds for the first five feet of height, and then adding 5 pounds for each inch of height after that. The resulting number could be adjusted plus or minus 10% to provide a "healthy range." So, according to that formula, the base number for a woman who's 5'5" would be 125 pounds. A wide variety of people and organizations still rely on this basic formula or a slight variation of it.

Here's the problem, and I'll use myself as an example, because I have data on myself, and it's just easiest that way: I am five feet tall. Therefore, according to the above formula, I should weigh 100 pounds, give or take 10 pounds. I do not weigh 100 pounds. I can't remember the last time I weighed 100 pounds. Nor do I weigh 110 pounds. I do remember the last time I weighed 110; I was 14 years old. What I weigh is about 119, which would mean, according to this formula, that I was on the verge of obesity and facing numerous weight-related health risks.

Even if I had no other way of gauging where I "should" be in terms of weight, that wouldn't seem right to me. I'm certainly not immune to distorted body image, and I can pine for a smaller ass and a flatter stomach along with the best of 'em, but even if I decided to believe someone who told me I should weigh 100 pounds, I suspect that it wouldn't be physically possible for me to lose 19 pounds without making myself really sick. This becomes more clear to me when I spend a few minutes playing around with calculations based on body fat percentages.

It can be difficult to obtain a reliable measurement of your body fat percentage, particularly if you're depending on someone who's using calipers to measure your skin folds, but who doesn't really know what they're doing. Many gyms and some doctors now have these fancy bioelectrical impedance devices that provide more accurate results. There's a margin of error, certainly, but if you take multiple measurements on different days under similar conditions, and then average the results, you'll be about as close as you can get without doing an underwater weighing.

So. The numbers. What the keepers of the fancy device tell me is that my body fat percentage at my current weight is around 21.8%. Of course, that doesn't mean anything unless you use some sort of chart to interpret it, and these charts can be totally inconsistent. In general, it seems that the charts you'll find from organizations dedicated to general health provide higher numbers in the "healthy" category than do health clubs or organizations that focus specifically on fitness. You can find a fairly typical general chart here, and a fairly typical health club version here. If you know your body fat percentage and your weight, you can use the formula from this page to figure out how many pounds of your total weight are fat and how many are lean body mass.

For example:

My current weight is 119, and my current body fat percentage is 21.8%. If you multiply those, you'll get a total for pounds of body fat.

(119 pounds total) x (.218) = (26 pounds of fat)

You can then subtract the pounds of fat from the total weight to figure out how much of your weight is muscle, bones, organs—that sort of thing.

(119 pounds total) - (26 pounds of fat) = (93 pounds of lean body mass)

Since the idea when you lose weight is to lose fat, not muscle, bones, and organs, you can use these numbers to come up with a much better idea of the kind of weight range that would be healthy for you. You can also use them to demonstrate just how bullshit some of the old formulae are.

For example:

If I think my goal weight should be 100 pounds, and I know how much lean body mass I currently have, I can subtract the lean body mass (because I want to keep all that) from the goal weight to determine how much fat I'd have at that weight.

(100 pounds total) - (93 pounds of lean body mass) = (7 pounds of fat)

Because you have all those figures, you can set up a simple equation to figure out how that translates to a new body fat percentage. If you're working with 100, the equation part is really unnecessary, but whatever. I'll write it out anyway.

(pounds total) x (body fat percentage) = (pounds of fat)

So...

100x = 7

Divide both sides by 100 to isolate the variable, and you get .07, or 7%. Looking back at this chart, we can see that women need 10-12% body fat to live. Even if I lost only fat on my way down to 100 pounds, I'd be lunching with Karen Carpenter. If I lost only fat to get to 110 pounds, the very upper end of that stupid formula's range for my height, my body fat would be 17%. While that percentage isn't dangerous, it's getting there. That chart I've been referring to lists the range for "athletes" as 14-20%, but it's important to remember that many athletes—particularly in sports like distance running, gymnastics, and skating—have body fat percentages that are way too low. (If you're interested in more specifics, here's an interesting article on the topic. I haven't fact-checked it, because I have a research fetish, but I also have limits.) Indeed, while the numbers vary for different women, many start to develop all sorts of problems, including amenorrhea, low blood pressure, and lowered bone density, when their body fat percentage drops below 17%. Clearly, 110 pounds isn't a realistic upper limit for me; it's barely high enough to be a safe low-end limit.

The point is not that this influential chart doesn't work for me. The point is that much of the advice we get about what we "should" weigh is terrible advice that can have devastating effects not just on our self-esteem, but on our health.

And that, my friends, is the story of why young gymnasts always look slightly deformed, why you should never rely on an actuary for health advice, and why you should love your ass. I can write a sentence like that if I want to, because even those of you who thought you were going to make it through this whole entry stopped reading when I wrote the word "equation." Still, I'm posting it anyway, because just when I find myself thinking that people already know this kind of stuff, I remember women I knew in college who taped pictures of Victoria's Secret models to their mirrors with annotations like "ME IN JUNE." Screw that. Screw the fact that I completely understood. And screw Victoria's Secret; they send me too many catalogs, and the last bra I bought from them has an itchy spot in the back.

Knocking you out with my Scandinavian thighs,
Shasta