Friday, January 25, 2008

What your Waist-to-Hip Ratio Says About Your Health

A few weeks ago I had my annual checkup with my doctor. The drill was the same it's always been, except this time her nurse took a measurement on my waist.

Immediately I saw the connection to the research I am familiar with on the WHR (waist-to-hip ratio). WHR is a favorite topic of evolutionary psychologists.

It all started with an Indian researcher named Devendra Singh who demonstrated that men express the most sexual attraction to women with an hourglass figure - and not just any old hourglass figure. Men, in samples drawn from around the world, including non-Western and non-Industrialized cultures, agreed that women who have a waist-to-hip ratio of .70 are the most sexy.

Right about now, you might be wondering how to measure your WHR. Measure the narrowest part of your waist and the widest part of your hips. Divide your waist measurement by your hip measurement - that gives you your WHR.

A .70 WHR is roughly equal to a 25 inch waist and 36 inch hips. Regardless of weight or BMI (body mass index), those proportions are considered the most attractive to men all over the world.

Why? Men find sexiest those women who are likely to be fertile and nubile, i.e. able to get pregnant. Women with smaller waists and wider hips:
* aren't obviously pregnant
* tend to be younger

* have more circulating estrogen

- all of which are associated with higher fertility. Ancestral men who preferentially mated with women who showed signs of fertility left more offspring than men who were indifferent to such signals. Those are the men alive today.

And, ancestral women with those signals produced more offspring.

Women tend to be pear shaped, as opposed to the more apple shape of men. Why are the sexes shaped differently? The answer is probably obvious, because women's wider hips are "good for childbearing," but the evolutionary mechanism isn't obvious.

You've probably heard of natural selection, but what about sexual selection? Sexual selection is another way that organisms change over time.

Rather than changing in response to different climate conditions or the presence of predators as with natural selection, under sexual selection, change occurs due to competition for mates. Women become more pear shaped over time because that's what men find appealing, and women with sexier bodies can get better, more "fit" mates.

Although Singh's and other similar research has been fairly criticized on the grounds of flawed measurement instruments (at right), subsequent research using more valid techniques has achieved the same results.

The key piece in all of this is that question of whether women with .70 WHRs are really more fertile. As it turns out, women with smaller WHRs get pregnant more readily, according to a study of female fertility clinic patients.

Of course, I'm scratching my head at all this wondering why, if I have the ideal WHR and BMI and hormone levels, why can I not get pregnant then? It's the curse of endometriosis, a condition made worse by frequent menstruation, that probably never existed in ancestral times because women got pregnant soon after they started menstruating and then nursed, weaned the baby, and became pregnant again over and over.

Estimates are that ancestral women only menstruated about 30-40 times in their entire life. Can you imagine that? The average women living now menstruates hundreds of times in her life. And that, my friends, is an evolutionary novelty.

Medical doctors have caught on to the trend of WHRs - except they're interested in what it signals about your overall health - not just your reproductive health. Smaller waists and wider hips are associated with better coronary and vascular health. It's that connection with estrogen. Estrogen is "heart healthy." Must be, because my cholesterol numbers came in the mail today and mine are as healthy as they get.

My HDL "good cholesterol" is 83 out of 89 (higher is better), and my LDL "bad cholesterol" is 66. It's supposed to be under 130. And I eat cheese all the time - and milk. It's genetics, I tell you. It's genetics. Diet makes it worse, no doubt. I'm not going to start eating mac and cheese at every meal.