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.

Cranberries

The Today show featured a short segment on cranberries and bogs. The announcer really wanted the cranberry grower to explain how the whole bog thing works, but all he could do was point out some short bushes with little red berries. Left hanging on the vine was the question of how one goes from there to the picturesque water filled bogs. I wondered the same thing myself, so here's what I found out about cranberries. They're really interesting berries. (I still don't think they taste particularly good!). The berries are harvested by flooding the field they're grown in (a bog that has peaty, acidic soil) and then agitating the water with this device to loosen the berries. The floating berries are then sluiced from the surface.

Cranberries are native to New England and grow well in acidic soil (just like azaleas & rhododendrons). The name is probably a variation on the colonial "crane berry" so named because the flowers resemble the sand cranes that could be seen eating them. The Ocean Spray company produces 90% of the world's supply, grown in northern climates (MA, WA, OR, BC) only because milder climates create problems with fungus.

Cranberries are also well known for promoting urinary tract health. And, it's not all hype. In 2002, JAMA reported a study that suggests persistent urinary tract infections that are resistant to antibiotics could be prevented by drinking cranberry juice. The researchers found that cranberry juice prevents 80% of bacteria from attaching to the cells of the urinary tract. These anti-adhesion effects have been isolated to compounds called proanthocyanidins - yep, a cyanide relative. Cranberry juice is a real, viable alternative to participating in the evolution of antibiotic resistant bacteria.

Speaking of that, recently my Newfie puppy had to visit the vet for what they labeled a bladder infection. They allegedly did a test that showed she did have an infection, and of course, sent us home with antibiotic pills. She still dribbles. So, now I'm thinking it wouldn't hurt to put her on a cranberry juice routine. She may not like the tart treat as much as she enjoyed that peanut butter pills, but maybe it would be a good long-term solution.

The Cranberry Institute reports that the bacteria that cause periodontal gum disease are also sensitive to cranberry juice. That seems like good reason enough to drink the stuff, but did you know that blueberries are just as good?

Blueberries, in addition to having the anti-adhesion properties of cranberries, also have anti-proliferation capacity. They prevent cancer cells from replicating. Cool.

And, blueberries taste much better!

The Rutgers Blueberry and Cranberry Research Center is working to breed berries that have higher concentrations of medicinal properties.

Soy & Phytoestrogens

Last week I finished reading an article from Hormones and Behavior about the metabolism of hunger and sex drive. Within it, I learned some more interesting factoids about the consequences of ingesting soy. I think I drink a lot of soy, and I also eat tofu occassionally, so I am interested.

I'm still trying to wrap my head around the wide-ranging article, to fit the pieces together myself, so I'll just report some of the more interesting elements of the story.

1 - Fat cells have estrogen receptors! Mice without working estrogen receptors become obese.

2 - Body fat distribution is more critical to long term cadiovascular health than body fat content or BMI. Gluteofemoral fat deposits are cardioprotective. So, if you have an hourglass figure (narrow waist with wide hips and fleshy butt and hips - an hourglass/pear figure rather than an apple) you're at reduced risk of heart disease. Also, women with a .70 waist to hip ratio (the hourglass figure) have higher fertility.

3 - Insulin levels are associated with visceral (deep belly) fat, whereas leptin levels are associated with subcutaneous gluteofemoral (butt, hips, thigh) fat. Hormones of the HPA axis (hypothalamus - pituitary - adrenal glands), such as cortisol, are also implicated in body fat distribution. Stress may cause you to put on more visceral fat.

4 - Eating disorders (of which the author seems to be primarily interested in obesity) may arise from changes in neural sensitivity to estrogen that occur early in brain development.

5 - These changes might be intitiated by exposure to phytoestrogens in our diet and pollutants.

So, evidently, consuming soy is cardioprotective and reduces the risk of developing obesity only when consumed as an adult. BUT - and this is a big but - consumption of soy during pregnancy or exposure of a fetus to soy and phytoestrogens actually increases the risk of cardiovascular problems and obesity.

Pregnant women and infants should not consume soy or any products containing phytoestrogens because the phytoestrogens bind to the body's estrogen receptors in the brain, various internal organs, and particular body cells like fat cells. This leads to organizational changes in the infant's brain that masculinize a female's body fat distribution after puberty: more visceral fat around the waist, less around the hips and butt. This places her at greater risk of developing heart disease and obesity.

The paper, however, focused on an evolutionary theory that there are brain mechanisms dependent on hormones that serve to signal an animal when it's time to eat vs. mate. The author explored the metabolic control of hunger inhibition, arguing that such a mechanism is adaptive because it would "bring the cessation of hunger and eating long enough to find and court potential mates." She suggests that the hormone leptin, known as a hunger hormone because high levels of it inhibit appetite, should come to be viewed as a sex hormone too. Evidently, leptin enhances sex behavior - in rats and mice. It stimulates the preference of having sex over eating. The author also argues that the hormone neuropeptide Y which is known as an appetite stimulant, should also come to be viewed as a sex hormone that stimulates the preference for food over sex.

Weight Regulation

One of the things I try to get across to students in my intro psych class during our unit on motivation and hunger is why people have so much trouble losing weight and then keeping it off for good. Millions of people struggle with this problem but wind up choosing a strategy that doesn't work. A typical diet involves restricting calories, which at first blush seems like the right thing to do. Pounds disappear one after another. Some may even reach their target weight but then put almost all of the weight back on despite following the same diet.

Why does this happen?

The answer lies in how our bodies are designed. Humans evolved in an environment that was very different from the one we now enjoy. The easy access Americans have to fatty, salty, and sweet calorie rich food is completely novel. Our ancestors probably had to travel long distances to acquire the nutrients they needed to survive, let alone thrive. What was available may not have been particularly nutritious or filling. Tubers, nuts, and fruit were staple items - meat a rare delicacy. Famines may have been a regular problem. Those who could slow down their metabolism in response to famine could conserve the fat and muscle they had stored and wait out the "lean times." Our bodies aren't prepared to deal with regular indulgences that we have access to now.

When a dieter consistently restricts calories over a period of time, the person loses weight but also winds up signaling the brain (the hypothalamus) that s/he is in the midst of famine conditions. The brain responds adaptively by slowing metabolism down. If the person eats the same amount, s/he will start gain weight again as the body "saves up." Restricting calories even more will exacerbate the problem and create new ones (malnutrition).

In order to keep the unwanted weight off, the body's "set point" has to be changed. The set point is the genetically determined weight the person tends to have when s/he isn't dieting, overeating or engaging in an exercise program. That set weight point depends on the person's metabolism and this is what has to change in order for the person to permanently keep lost weight off. Metabolism depends on how responsive the hypothalamus is to the various signals that it receives from the body and the concentration of 'hunger hormones' such as leptin, neuropeptide Y, ghrelin, and orexin circulating in the bloodstream.

You can think of the hypothalamus as a thermostat for hunger regulation. Reduced food intake = slow down metabolism. Increased food intake = rev up metabolism. Because the human body evolved in an environment that saw recurrent famines, it is far easier for us to slow our metabolism down than to speed it up. When a dieter loses weight but then starts to gain it all back, that's because the body is doing exactly what it's supposed to do.

So, the real question is how to speed up one's metabolism and permanently reset the body's set point.

One way to try to do this is to get more exercise. Unfortunately, doing this while also cutting calories, releases a whole new wave of metabolic changes that are designed to put the weight right back on! For example, research from the NIH suggests that when a person loses weight and exercises more, thereby creating an energy deficit, ghrelin (an appetite stimulant) kicks into high gear.

That raises the question of whether it's even possible to permanently change a person's set point.

Lactose Intolerance

Over the weekend a good friend of mine visited for our college reunion. She's lactose intolerant and likes to enjoy ice cream and other dairy products so she brought lactase pills along with her so she could digest the milk sugar lactose. She was also told by her pediatrician the day after she returned home that she's got to fatten her one year old daughter up. I asked her how she's supposed to do that. Cheese! Makes sense, but she's worried her daughter might be lactose intolerant too. Being fully capable of digesting the stuff myself, the concept of lactose intolerance is not something I spend much time thinking about... until recently.

According to Steve Lewis, a professor of Darwinian medicine, mammals lose the ability to digest milk with age. This might "form a biological mechanism whereby the ties between mother and child are broken so that she can go on and have more offspring and the child can go and have offspring of its own." Symptoms of lactose intolerance include gas, bloating, abdominal cramps and diarrhea result. The NIH estimates that in the U.S. about 15% of people of European descent have it. Half of Latinos, 60-100% of Native Americans, 80% of African Americans, and 90% of Asian Americans are lactose intolerant. The ability to digest milk depends on how heavily a culture depended nutritionally on the milk of their herded animals.

What is really interesting to me from an evolutionary perspective is that lactose intolerance is something all humans should experience yet many don't. Relatively new research has discovered a genetic mutation that gave some adult humans the ability to digest lactose. This occurred sometime in the last 5,000-10,000 years and coincides with the origin of pastoralism in Europe.

This finding poses challenges to evolutionary theories about human behavioral adaptations (such as males' preference for mating with nubile women) that are thought to take hundreds of thousands of years longer to develop in a population. EPs can't go back in time to determine what kind of ecological conditions human ancestors lived in at the time we were evolving these adaptations (the so-called "environment of evolutionary adaptedness"), so most EPs infer what kind of behavioral adaptations would have been most adaptive for our ancestors by examining the ecological conditions of extant human hunter-gatherers. They assume the living conditions are essentially the same and that not enough time has passed for new adaptations to take hold, so if it would be adaptive for hunter-gatherers now it was probably adaptive in the past too. Obviously trouble arises when new evidence suggests that humans can evolve faster than expected. If a gene for making lactase well into adulthood can take hold in the last 10,000 years it is also possible that a gene for constructing hypothalamic-visual cortex connections in the brain that fire maximally for men viewing nubile young women could take hold that fast too. I seriously doubt that there was ever a time when the average man was turned on by the sight of a pre-pubescent or wrinkled old woman. It wouldn't make much sense for successful reproduction.

However, there are other adaptations that are more controversial and could conceivably be a product of relatively recent changes. The female orgasm, the desire for men to have more sex partners than women, sexual jealousy, monogamy, etc.

The discovery that lactose is newly digestible does NOT mean evolutionary psychology is a rotten paradigm, as some would have it (David Buller), but it does mean that care needs to be taken when hypothesizing adaptations that assume nothing has changed within the last 10,000 years.

As for my friend's daughter, she should be able to digest cheese just fine. Lactose intolerance doesn't set in until later in life and is a recessive trait, so if her dad can still digest lactose, she should be able to later in life too.