Has eliminating hookworms made people fatter?

Okay, yes, obviously when you take the gut parasites out of people, they tend to gain weight immediately after. That’s not exactly what I’m talking about.

First, let’s assume you come from a place where humans and hookworms have co-existed for a long, long time. The hookworms that just about everybody in the American South used to have appear to have come from Africa, so I think it safe to assume that hookworms have probably been infecting a lot of people in Africa for a long time. I don’t know how long–could be anywhere from a few hundred years, if they’d come from somewhere else or recently mutated or something, or could be tens of thousands or hundreds of thousands of years, if they’ve just always been hanging around. Let’s just go with tens of thousands, because if it wasn’t them, it was probably something else.

Over a few thousand years of constant infection, you’d expect to develop some sort of biological response to minimize the chances of death–that is, your ancestors would have evolved over time to be less susceptible to the parasite. Obviously not getting the parasite is one great way to avoid getting killed by it, but let’s assume that’s not an option.

Another solution would be to just absorb food differently–faster, say, or in a manner that circumvents the parts of the gut that are normally infected. Over time, humans and parasites might tend toward an equilibrium–humans stepping up their digestion to make up for what’s lost to the parasite.

Remove the parasite, and equilibrium is lost: suddenly the human starts gaining a lot of weight, especially compared to people from populations that did not adapt to the parasite.

That functional a gut isn’t needed anymore, but it might persist for a while if there are no counter-evolutionary pressures.


5 thoughts on “Has eliminating hookworms made people fatter?

  1. […] Increased gender dimorphism = lower IQ? Genetic Aristotelian Moderation,  Species is a Social Construct: My Grandfather’s Totally Badass Dog, Cats are Cuckoos, Hey, DNA: What is it good for? Light and BMI, Live Fast, Die Young: The amazing correlation between self-control and not dying, You Probably Aren’t Adapted to the Paleo Diet, “Ancestral Microbes”, Is Acne an Auto-Immune Disorder? Has eliminating hookworms made people fatter? […]


  2. Do you mean African American obesity rate? If hookworm elimination was the case, black people would get fat in every hookworm free area of the world, but they aren’t especially fat except in the US. Almost all are normal to skinny here. Poorer is statistically fatter, but I don’t even see black garbage collectors who are obese. They’re mostly Caribbean and have solid culinary traditions. Perhaps traditional cooking vs. standard american diet is the difference.


    • It’s been a long time since I wrote this post or looked at any of the relevant data, but are those black folks even from the same ancestral ethnic groups? Were their ancestors all adapted to hookworms, or do some hail from regions without them?
      I’ve a chart of obesity rates (by gender) in different countries, and amusingly South African and Egyptian* women are both fatter than American women. (Women are more likely than men to be obese in almost every country.) By contrast, women in Uganda and the DRC are much more likely to be slim.

      Obviously there’s more than one thing going on with weight, even if the elimination of parasites (in the developed world) is part of the picture.

      *Yes I know Egyptians aren’t Subsaharan Africans; I only mention them because there are so few groups fatter than Americans.


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