When I asked Anne Fausto-Sterling about a related issue a few years ago, she told me that she suspected that our brains and bodies were so different from prehistoric humans because of such radical change (I assumed in behavior and environment) that she found most evolutionary explanations for modern behavior patterns to be dubious. I guess I share her dubiousness. One of the principal ways that we seem to differ so profoundly from our ancestors that comparison fails us, in my opinion, is this pattern of inactivity and sedentary life. At least in my view, sedentary life is so UNLIKE anything our ancestors might have encountered that coming up with evolutionary scenarios that include it are suspect.

What I’m saying is that sedentary existence is such a radically different environment than what evolutionary psychologists suggest is humanity’s ‘environment of evolutionary adaptation’ that all bets are off as to how we will respond physiologically. Put a microbe in a glass of Coca-Cola, and it will react, but the environment is so alien to anything it would conceivably encounter outside that glass that it’s difficult to say whether its activities are any realistic predictor of what that microbe would have been like in a different environment. The problem with studying humans is that it’s very hard to find anyone living outside the glass of Coca-Cola when it comes to certain environmental characteristics.

That’s where the inherited factors come in. Everyone anecdotally knows of individuals who eat many calories and move hardly at all, yet are slender or “average.” Why does Evolution 101 fly out of our heads when we talk about fatness? Human populations aren’t genetically uniform.

What I’m missing here is a discussion of *why* we would have genes leading to fatness in the first place. It seems to me that populations would support a range of genes, where some people would be able to withstand starvation better than others. Speculatively, it may be that the first diet (“I weigh 150, but I’m so fat, I have to weigh 135″) provides the biological “cue” that starvation is imminent, thus triggering particular “thrifty” genetic responses in some.

This is a different situation than individuals with specifically damaged genes (whether they involve leptin or not.) Thus you have “freak show” type television shows about extremely large individuals, with the covert message that if “we” keep eating “junk food,” “we” are all going to look “like them.” But as Kolata points out in her book, naturally “average” people who participated in overeating experiments did gain some weight, but lost it when they reverted to their normal eating patterns. So there is something (most likely) genetic going on with these extremely large people that is possibly *different* from having a “thrifty” constitution.

In my take on your comment, you are reacting against an equally determinative assumption–of willpower and an ability to control body shape/thinness–as well as against the stigma accompanying weight in the US. And I actually agree with you. So I applaud when you say about Kolata’s argument, “it’s a much more carefully worded and circumspect claim that “you may not be able to be arbitrarily thin”.” The moralizing side of things is particularly pernicious at times from both the science and the popular side, and even the moralizing gets naturalized (see my critique of Pinker back in January). So for me it was great to see you come over and really bring that out.

I am planning to post in the near future on some of the physiology and variability, so I hope you check back in to make sure I am not veering too far to one side or another.

I hear what Fatfu is saying, and I understand also the activist agenda; both the key point Fatfu makes and the agenda are important. But from my perspective as a researcher on exercise, neurology, skill, and sometimes even evolution, I have a different view. I don’t buy the Supersize Me scenario in one sense; I think that, given what would have been normal levels of exercise even 100 years ago, the all-MacDonalds diet might (MIGHT) not have been unhealthy for humans (although some of the health effects in that movie freaked me out). That is, in cases like the Inuit, we know human groups that have gotten what can only be considered shockingly ‘bad diets,’ by modern dietitians’ standards, who still didn’t have the health problems we associate with obesity. Usually, researchers look to something in the diet to explain why people who ate high quantities of animal fat or red meat or unvarying diets didn’t get health problems; was it fish oil or nuts or some other magic ingredient.

But the overwhelming difference, to me, is sedentarism. Our society is, in my opinion, so different from others NOT because of what we eat — humans have eaten all sorts of things and seldom consult with a reputable nutritionist before doing so — but because of how little we move. Estimates on movement in foraging societies are always very high; I’ve recently read 12 miles per day, average, but I’ve also been looking at extreme cases, and they are stunning. Native American groups who ran very long distances as part of festivals and inter-group competitions, distances in the hundreds of miles.

Even in agricultural societies, people also moved a hell of a lot; it wasn’t just foraging. A researcher stuck pedometers on Amish people, a group not known for its low-fat diet or for their obesity problems, and found that people were walking miles every day. One guy apparently was walking around 25 miles a day behind a plow, which wouldn’t have been easy miles. My wife’s grandmother just told me that she and her brothers and sisters used to walk 4.5 miles to and from school — 9 miles a day — and that was before they started to play sports or have fun.

As Drs. Rainer Hambrecht and Stephan Gielen argued in an essay in The Lancet in 2005, the amount of energy expended by kilogram of body weight is estimated to be less than 40% today of what it was in ‘the Paleolithic.’ (I’m a little uncomfortable with the assumptions about time periods we can’t actually do research in, but the comparative data makes this assertion pretty hard to contest.) Contemporary estimates are that 40% of the US population does NO exercise. We have created an environment in which movement is not necessary when, in most human niches, people are constantly moving. We all know the stories; people walking miles to collect wood or carry heavy jars of water, hunters stalking prey for miles, people walking for days to travel. It’s just not something most of us do.

Given this staggering difference in activity levels, the question I would ask is not, how do genes make some people obese, but rather how on earth does anyone NOT get obese at low activity levels? We know that body fat itself is pretty energetically cheap to keep on the body; it doesn’t add too much to the body’s ability (or need) to metabolize calories, so once you’ve got, you pretty much get to keep the fat for free. I’m not trying to get all preachy, as Fatfu suggests is the usual route, but rather to point out that, for me, the research question is not, ‘what is the gene for obesity?’ but rather, what the hell is it about the people who DON’T get obese given that we’re in such an odd situation for our physiology?

People sometimes suggest that over-eating is a kind of pathology, often suggesting that it has to do with psychological problems. They also imply that satiety is a problem; some people are genetically predisposed not to feel satisfied when they eat. I don’t know. But I do know that animals are pretty prone to over-eating, too, as my increasingly fat Labrador retriever and two cats attest. And I know that our horses, if they manage to get their teeth on a bag of feed, will gladly eat until they make themselves very sick. We had a real scare with one of them due to over-eating. And we have many ethnographic and travelers’ accounts of populations with virtually no levels of obesity eating tremendous amounts of food when they have it; I read in grad school a Jesuit missionaries account of how Canadian Indians ate when they got ahold of game during the winter, and they would blow away the most impressive binges in McD’s in terms of an orgy of gluttony. But then again, the group bordered on starvation in between successful hunts in the winter (thanks Marshall Sahlins for assigning that one).

I agree with Fatfu that there’s a bit of an obesity hysteria, but when you start to look at the difference in activity levels in our environments, it seems pretty clear (at least to me) what the ’cause’ of weight gain is. The point is clearly not to ‘go back’; who would want to have whole communities periodically starving, or force everyone to work at hard manual labor. Moralizing the issue — suggesting that fat people are weak or immoral, or that the parents of fat kids are irresponsible — is hardly helpful (or even accurate), but I also think that the argument that people are just genetically predestined to be obese is equally inaccurate (and probably unhelpful). It may influence the growing social stigma placed upon obesity, but it’s hardly the whole picture of what is leading to changes in our bodies.

Understanding this global picture of the body and energy reframes the question, for me, about genetic contributions to obesity. Seeing obesity narrowly, bounded by Western ideals of body type and moral assumptions about food, seems to make ‘the obesity problem’ distorted and individual, and it leads to questions like, ‘what are the genes that contribute to obesity?’ Clearly, given this screwed up environment, some people may have genes that, somehow, buck the almost inevitable energy imbalance due to sedentary life. Or maybe there’s something psychological about those who stay thin in spite of rocky road ice cream, Coca-cola, pizza, and family holiday feasts that makes them deviant. But for me, at least, knowing the scorecard in a broader perspective makes me more interested in what is odd about those who stay thin given this situation.

Reference

Hambrecht, Rainer, and Stephan Gielen. 2005. Essay Hunter-gatherer to sedentary lifestyle. Lancet 366: S60–S61.

My disagreements. Yes, Kolata and the molecular biologists are giving us the tidy “no loose ends” version. And there are a lot of loose ends out there. But that’s true of any nature/nurture debate. And the evidence that weight is physiologically regulated, heritable, and that weight loss strategies don’t really work, while not bulletproof, are so strong – especially when compared to the degree to which most of us have been convinced of the exact opposite – that it’s understandable that she would present the most forceful case she could without burying herself in the muck that any nature/nurture debate engenders.

You’re also misstating her case a little. Her ultimate argument isn’t that it’s all genes or that environment is unimportant, it’s a much more carefully worded and circumspect claim that “you may not be able to be arbitrarily thin.” Which I think is the very least you can say given the evidence.

You’re doing a lot of very interesting picking at the margins of the argument (some of which I enthusiastically agree with, some of which I don’t). And while I think pulling at those threads is necessary and important, and there are deep philosphical issues to contend with, I gotta say. You risk missing the forest for the trees. Yes, environment matters. Yes, nature/nurture is a quagmire. But weight is not just 0.8 or 0.7 or 0.5 heritable. It’s REALLY heritable. No, really.

What Kolata and the molecular biologists are trying to say is not that biology is destiny, but for some traits biology is more destiny than it is for others. And weight is one of those things for which it’s definitely more destiny. And that’s hard to get across with numbers. On its own just saying that a given trait is 50% heritable or 80% heritable is kind of meaningless – for one thing people interpret the number any way they want. “50% of fat people are fat because of lifestyle.” Or “50% of your weight is genes, 50% is McDonalds.” “If we ate paleolithic we’d be 50% thinner.” (It reminds me of the joke from The Hitchhiker’s Guide: What’s the meaning of life? 42. Now you have to go back
and figure out what the question was. The heritability index is an excessively precise answer to a question we can’t remember anymore.)

Here’s my unscientific approach. I know you don’t like twin studies, but it’s twins. In one of my posts on fat fu (‘twins”) I linked to a gallery of photos from a twin festival. I think they give you a visceral feel for just what a heritability index of 0.70 or 0.80 (or 0.50 if you prefer) really means in the real world. I don’t think it’s possible to look at those pictures and not at least begin to see the problem with nitpicking to death the bald fact that stares you in the face – that weight is, yes, incredibly heritable. And honestly, I think people for whom this is all academic or mathematical need to look at them as a reality check. Those photos don’t erase environmental influences but I think they put bounds and context on how much you can expect nurture to explain or “fix” human variation.

Kolata’s also countering a group of people who are so singleminded about making the nurture case that they haven’t even noticed that they’ve thrown under the bus -and backed over several times – the people they’re hoping to “help.” It’s one thing to argue that high fructose corn syrup has an impact on weight, or that exercise is helpful – it’s an entirely different thing to completely discount physiology, genetics and human variability and allow millions of people to be demonized and scapegoated in the global war on fat.

Because the real philosophical question we’re wrestling with is not so much how much can we blame on nature and how much on environment, but why do we construct certain traits in a moralizing way and others as morally neutral? Autism and schizophrenia are good case studies, because genetic models were important for shifting the focus away from models which blamed parental neglect and rearing (nurture). But for both of these disorders, the heritability studies are actually pretty mixed, and show much lower heritability than for fat. If somebody had wanted to pick the “nature” argument apart for either disorder and toss blame back on the parents they would have been in a much stronger position than we are when it comes to fat.

The comparison is important, because at the moment not only are parents being chastised for their children’s weight, there’s talk (at least from the fringes) about prosecuting parents of fat children or having fat children removed from their parents’ homes (which has been done in rare cases in the U.S. and U.K). We’re very much in the situation with fat that we were in the past with children who were autistic. Actually we’re in a much worse situation since we’re in the middle of a global hysteria about weight and it’s unclear to what extremes that will drive public policy.