Friends & fat

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In the McArdle vs. Frum diavlog I alluded to earlier there was a dispute centered around two seemingly contradictory results. First, the fact that heritability of obesity is rather high, in twins-separated-at-birth studies the correlation between monozygotic twins raised apart is on the order of ~0.75. And yet people tend to track the weight of their peer group. The causality here has to be teased apart of course, but consider this study, The presence of friends increases food intake in youth:

Design: Twenty-three overweight and 42 nonoverweight youths had the opportunity to play and eat with a friend (n = 26) or with an unfamiliar peer (n = 39). The dependent variables of interest were the amount of nutrient-dense and energy-dense foods children consumed and their total energy intake.

Results: Participants eating with a friend ate substantially more than did participants eating with an unfamiliar peer. Furthermore, overweight youth, but not nonoverweight youth, who ate with an overweight partner (friend or unfamiliar peer) consumed more food than did overweight participants who ate with a nonoverweight eating partner. Matching of intake was greater between friends than between unfamiliar peers.

Naturally twins raised apart were not placed into a “design” whereby they were forced to eat with strangers. Rather, they selected their peer groups. Heritability of many traits increases with age because individuals seek out particular environments which eventually dampen the “noise” which reduces the correlation between those with similar genetic propensities. Assortative friendship by weight then might result in amplifiers of mean deviation from phenotypic norms; that is, thin peer groups might model specific behaviors and apply certain pressures which differ greatly from overweight peer groups. Gene-environment correlation. So naturally in the interests of public health we need integration across weight classes….

Also see ScienceDaily.

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  1. I’m a big believer in habits. It’s too hard to make good decisions over and over, but it you can pick up a good habit, you’re likely to come out better.

  2. An interesting question about weight is how long has slenderness been a mark of upper classness? 
    It doesn’t seem to have been in the days of JP Morgan and Wm Howard Taft, although I wouldn’t be surprised if slenderness wasn’t considered an aristocratic trait going much farther back.  
    Anyway, at some point, the fat cats stopped being fat. If this social attitude stays consistent over generations, then genetics will start playing a role as more slender people are recruited via marriage and affinity to the upper classes and more chubby people are expelled or kept away.

  3. Despite having Taft as a specimen, I’m wary of taking literally a folk idea, the fat cat, that is formed partly from resentment and may have been propagated partly by people who were actually underfed. 
    I have heard of some people – was it Inuit? – that preferred fat women. If it was Inuit, the climate of their homeland makes that more understandable. Rubens is of course the guy most often adduced in favor of the claim that tastes have majorly changed, an idea that was repeated even by the fairly non-PC Matt Ridley. Well, one can rapidly look at dozens of his paintings here, which I just did for the first time: 
    …and I really don’t see it. His women are quite strong boned and very muscular, and he likes to be sternly realist about fat bunching up under loose skin when it is compressed by a figure’s bent trunk or limb. But the actual amount of fat looks barely above today’s average ideal. Bone and muscle are moving them off the average ideal of beauty as much as fat is – and even so they are still pretty attractive. Consider this Ceres, who is thicker than Reubens’ average woman, alongside a Venus who is thinner yet with more fat: 
    The deep cleft down Ceres’ spine illustrates that we are looking at beef, not butter, and that seems typical for Rubens. This Ceres has some real latissimi, and could probably do a lot of pull-ups and fare quite well as a varsity oarswoman. She also shows biceps and triceps on her arm, not flab, and is attractive except for her thick waist. The one really fat person is this Bacchus, who is obviously receiving anything but flattery from the painter: 
    I don’t see evidence for a big change in the ideal – what I expected to see from the way some people talk about Rubens, I don’t see. In the year 2410 people may claim almost the same sort of thing about Kokoschka’s 20th-century paintings of the broad-framed beauty Alma Mahler: 

  4. I agree with the point about habits. However, feeling hungry isn’t really a habit. Perhaps a person whose is likely to become overweight could develop healthy eating habits until he was in a situation other than his routine and would alter his behavior to eat far more than a person who did not feel hungry. I thought I saw something about adopted kids’ weights being more like their biological parents than like their adoptive parents. An uncle and aunt in our family who were overweight adopted two infants who both grew to adulthood, now aged 50 and 53, one boy, one girl, Both are very thin. Two fat parents pushing food at them for years and years, yet still thin. They aren’t runners or anything, and have just regular jobs.

  5. Anyway, at some point, the fat cats stopped being fat. If this social attitude stays consistent over generations, then genetics will start playing a role as more slender people are recruited via marriage and affinity to the upper classes and more chubby people are expelled or kept away. 
    This is certainly possible, although it could be moot if someone invents the anti-fat pill, which I think is a real possibility. Even if someone does, general attractiveness could start to bubble up into the upper classes. I’ve seen studies showing that more attractive people tend to make a bit more money. Right now, I think this is primarily an environmental effect, but at some point it could become genetic.

  6. The idea of fat being a mark of higher class goes way back. If you look at paintings in Central Europe, you’ll notice that many artists added in pot bellies to the pictures of otherwise trim military officers and nobles to “fatten” them in the eighteenth and nineteenth centuries. In fact I saw a few such pictures in a Slovakian castle just recently. Art historians agree that this was done deliberately.