The sample included 215,000 adults who reported one or more ethnicities, height, weight, and other characteristics through a mailed survey. … The highest age-adjusted prevalence of overweight (BMI greater than or equal to 25) was in Hawaiian/Latino men (88% ; n = 41) and black/Latina women (74.5% ; n = 79), and highest obesity (BMI greater than or equal to 30) rates were in Hawaiian/Latino men (53.7% ; n = 41) and Hawaiian women (39.2% , n = 1,247). The prevalence estimates for most admixed groups were similar to or higher than the average of the prevalences for the ethnic groups with whom they shared common ethnicities. For instance, the prevalence of overweight/obesity in five ethnic admixtures–Asian/white, Hawaiian/white, Hawaiian/Asian, Latina/white, and Hawaiian/Asian/white ethnic admixtures–was significantly higher (P < 0.0001) than the average of the prevalence estimates for their component ethnic groups. … The identification of individuals who have a high-risk ethnic admixture is important not only to the personal health and well-being of such individuals, but could also be important to future efforts in order to control the epidemic of obesity in the United States.
Although Razib considers some interesting genetic explanations, my own hunch is that cultural factors are the more important variable here. As Michael Pollan points out, one of the central problems with American eating habits is the absence of an indigenous food culture. Instead of relying on time-tested habits – modern Tuscans are still enjoying their 18th century peasant diet, full of legumes, durum wheat pasta and bitter greens – we’ve switched over to a diet based on Nabisco’s bottom line and horribly misguided agricultural subsidies, which encourage farmers to grow high-fructose corn syrup. This shiny new diet, wrapped in the impressive vocabulary of nutrionism, has erased all the culinary wisdom accrued over the centuries:
In many cases, long familiarity between foods and their eaters leads to elaborate systems of communications up and down the food chain, so that a creature’s senses come to recognize foods as suitable by taste and smell and color, and our bodies learn what to do with these foods after they pass the test of the senses, producing in anticipation the chemicals necessary to break them down. Health depends on knowing how to read these biological signals: this smells spoiled; this looks ripe; that’s one good-looking cow. This is easier to do when a creature has long experience of a food, and much harder when a food has been designed expressly to deceive its senses — with artificial flavors, say, or synthetic sweeteners.
Note that these ecological relationships are between eaters and whole foods, not nutrients. Even though the foods in question eventually get broken down in our bodies into simple nutrients, as corn is reduced to simple sugars, the qualities of the whole food are not unimportant — they govern such things as the speed at which the sugars will be released and absorbed, which we’re coming to see as critical to insulin metabolism. Put another way, our bodies have a longstanding and sustainable relationship to corn that we do not have to high-fructose corn syrup. Such a relationship with corn syrup might develop someday (as people evolve superhuman insulin systems to cope with regular floods of fructose and glucose), but for now the relationship leads to ill health because our bodies don’t know how to handle these biological novelties. In much the same way, human bodies that can cope with chewing coca leaves — a longstanding relationship between native people and the coca plant in South America — cannot cope with cocaine or crack, even though the same ”active ingredients” are present in all three. Reductionism as a way of understanding food or drugs may be harmless, even necessary, but reductionism in practice can lead to problems.
Ok, back to this paper on mixed-race adults and obesity. I wonder (and this is pure hypothesis) if one of the driving factors behind the data is the absence of food culture. The best way to illustrate the point is to describe my own experience. My father was raised on a steady diet of Jewish-American foods, from pickled herring to brisket. If left to his own devices, he would eat nothing but pastrami on rye with a smearing of spicy mustard. My mother, on the other hand, was raised on a Pennsylvania-Dutch diet, full of agrarian dishes like mincemeat pie and pickled red-beet eggs. Her uncles were all corn farmers.
So what food culture did I inherit? A smattering of everything. I like most deli foods – gefilte fish remains a hurdle to overcome – and I’ve learned how to pickle my own red-beets. I always have lox in the fridge and one of my favorite recipes is for sweet-corn chicken soup. (Thanks, Grandma!) But the point is that my food culture is all a la carte – I pick and choose what I like and leave the rest. My eating habits are thoroughly post-modern, severed from any ethnic or cultural tradition. While that culinary freedom certainly comes with advantages – my pantry is stuffed with everything from dried sweet corn to sichuan pepper – I’ve also missed out on some evolved wisdom. A genuine food culture, after all, isn’t merely a collection of recipes – it’s a way of life.
So I wonder if part of the explanation for the link between mixed-race adults and obesity is that, like me, these people are less likely to inherit a set of culturally specific food traditions. Razib notes that this lack of food culture might also lead to a diet that doesn’t mesh well with genetics:
Different populations have different propensities toward different food stuffs; e.g., consider the amylase and lactase examples. Perhaps mixed-race children because of their bicultural background are exposed to a hodge-podge of dietary regimes which aren’t optimal to their genetic makeup, which are relatively recent and so might not have a ready made cuisine?