What is Overweight?

Have you ever wondered where the BMI guidelines come from? Could they be completely arbitrary just like all the most of the other health advice we’ve been dished out? A new study published in JAMA provides some clues:

A new US study suggests that while the link between weight and causes of death varies considerably, being modestly overweight may actually lower death risk in a number of circumstances by providing the body with essential nutritional reserves during recovery from illness and major operations.

What is interesting here is not only that it shows a BMI of 18-25 may not be a healthy objective, but it calls into question what “overweight” really means. Isn’t the weight that confers the longest longevity the “ideal weight” and that weights under and over that ideal are in fact “underweight” and “overweight”?

Or have we confused sexy with ideal?

Although it is assumed that we are naturally attracted to whatever/whoever is healthiest, this is not necessarily the case. Creatures often find characteristics sexy which confer little health benefit. A peacock’s tail is no doubt a hit with the peahens but it is also a bit of a drag if he needs to make a run for it.

It doesn’t take much imagination to see that humans have preferred for a number of traits which, through the generations, have made us into very odd looking apes – naked, big breasts, long head hair… None of which seem to do much in the fitness department other than to signal sexual fitness. So have these preferences hijacked scientific thinking about what is ideal for health?

5 thoughts on “What is Overweight?

  1. I think body fat percentage is probably a better measure. I am 5′ 3″ and currently have 31% body fat and weigh about 147-148 lbs, which means I have around 101-102 pounds of lean body mass. Yet according to the BMI charts, I could weigh 105 lbs and still have a “healthy” BMI of 18.6. Assuming that it is undesirable to lose any lean body mass, this would put me at around 5% body fat, putting me at risk for amenorrhea (and god only knows what else, but I mention amenorrhea because of its affect on fertility – sexual selection is weird – we favor skinny women who probably aren’t even fertile)! A healthy body fat percentage for women would be more like 25% to 27%, which would give me a healthy weight of a little under 130, which is what I’m now aiming for.

    Dianne (aka Migraineur)

  2. I’ve had the same problem. I actually had a medical exam in which I was told to lose “x pounds of fat and y pounds of muscle.” It’s madness.

  3. By the way, Jared Diamond had an interesting take on sexual selection as it relates to things like the peacock’s tail. Extravagant displays of basically useless stuff show that the critter is so healthy it can afford to be wasteful. If you are an adult male peacock and have a gigantic tail, that means you can – and most likely have – escaped from enemies in spite of the disadvantage, which means you are fit in the extreme. He compares it to diamond engagement rings – useless, except it shows that the guy has extra resources.

    I think favoring skinny (i.e. infertile) women is the opposite – picking someone with no resources to spare at all. It doesn’t make sense from an evolutionary standpoint, and it’s part of my argument that evolutionary psychology can’t explain everything about human behavior. :)

    Miss Bossy, don’t give up a single ounce of your muscle!

    By the way, it’s long been known that people who weigh more have stronger bones. It doesn’t matter whether the weight is fat or muscle; the increased load strengthens bone.

    Dianne (aka <a href=”http://migraineur.wordpress.com”)Migraineur

  4. Pingback: What’s Your Ideal Weight? « The Migraineur

  5. Pingback: Calculating Life Expectancy « Harpoon

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