The Evolutionary Biology of Obesity

June 7th, 2012 at 8:33 am

A few weeks ago, I wrote about the political economy of the obesity epidemic.  Here, from a great oped in yesterday’s NYT, is the evolutionary science behind both the problem and the solution.

Here’s the argument (though I strongly urge you to read the extremely well-crafted piece):

Since sugar is a basic form of energy in food, a sweet tooth was adaptive in ancient times, when food was limited. However, excessive sugar in the bloodstream is toxic, so our bodies also evolved to rapidly convert digested sugar in the bloodstream into fat. Our hunter-gatherer ancestors needed plenty of fat — more than other primates — to be active during periods of food scarcity and still pay for large, expensive brains and costly reproductive strategies…

Simply put, humans evolved to crave sugar, store it and then use it. For millions of years, our cravings and digestive systems were exquisitely balanced because sugar was rare. Apart from honey, most of the foods our hunter-gatherer ancestors ate were no sweeter than a carrot…it wasn’t until very recently that technology made pure sugar bountiful.*

Here again we run smack into the economics—technology (and trade) has allowed us to push out the supply curve, and thus lower the price, of a food source we crave but that is bad for us in such quantities.

In this regard, as the author puts it, Mayor Bloomberg’s move to ban large sugary drinks, though admittedly “paternalistic,…is not an aberrant form of coercion but a very small step toward restoring a natural part of our environment.”

Libertarians will squawk, and not unreasonably.  But as long as the externalities I document in my earlier post persist—and they’re getting worse—the rationale for such policies—bans, Pigouvian taxes, consumer education—is strong and getting stronger.

When science, evolutionary biology, and simple economics all point in the same direction, it’s probably wise to head that way.

We humans did not evolve to eat healthily and go to the gym; until recently, we didn’t have to make such choices. But we did evolve to cooperate to help one another survive and thrive. Circumstances have changed, but we still need one another’s help as much as we ever did. For this reason, we need government on our side, not on the side of those who wish to make money by stoking our cravings and profiting from them. We have evolved to need coercion.


*One question: what about geographies where sugar wasn’t rare, like the tropics (I had some incredibly sweet pineapple this AM)?  If this theory is correct, wouldn’t it predict that earlier civilizations in such areas were more prone to obesity?  Or is this more about processed sugars?

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13 comments in reply to "The Evolutionary Biology of Obesity"

  1. William Mooney says:

    My understanding is that it has to do with the types of sugars we are consuming today. I started looking into this after reading this story:

    • DonB says:

      Try watching this YouTube presentation by Dr. Robert Lustig of UCSF on his hypothesis that the extra sugars in the American diet break each of the two feedback loops that in a less-sugar intense diet help the brain stop wanting to eat (satiety) from the stomach being full and another through leptin.

      This link provides further links to a shorter, more recent talk.

  2. Bumpa says:

    Moderation in all things —- including moderation!

  3. Erick Cobb says:

    Fruits are most likely not as naturally sweet as we assume they are. This is because we tend to find a mutant and then proceed to clone it. Fruit cloning (as opposed to animal cloning) has been possible for a couple of hundred years. It is the reason why Gros Michel bananas are extinct and Cavendish bananas may become extinct within the next 10 years.

  4. Mike the Mad Biologist says:

    Sugars in processed foods and those added into liquids are easier to access (think baby food as an extreme example). The other thing to remember is that ancestral forms of many fruits (those pre-agriculture) are smaller and less sugar rich (you’re competing with other fruits, not Pepsi). Finally, even in the tropics, wild plants typically have seasonality in their fruit production.

  5. RMGHicks says:

    Our diet has been so modified over time that the truth is we haven’t eaten like hunter-gatherers for thousands of years. There is a book about how our agriculture evolved (Pandora’s Seed by Spencer Wells). A good read if you are curious.

  6. Chris says:

    Humans are like basically every other animal… we’ll eat ourselves to death if given the chance. You can see it in everything from goldfish to dogs. I remember having to carefully monitor how much food I gave my fish so I didn’t over feed them, and my dog growing up would literally tear open cans of food to eat and got so fat we had to lock away any possible food source.

    That being said, I would prefer a ban on beverages over a certain number of calories, and not based on the size. When I’m walking around the city on a hot summer day, 16 ounces of liquid just doesn’t cut it.

  7. Rima Regas says:

    It is about the processed sugars. They do bad things to our metabolism. It’s also about where these processed sugars are found. They’re in almost everything that you do not cook or bake from scratch. The new study that was done on HFCS was done in a hospital setting and it didn’t matter how much corn syrup was ingested, the adverse effect was the same. People in the tropics still eat pineapple, heck they export it, but they now also eat foods modified with high fructose corn syrup, and are consequently as prone as we are to obesity.

    I highly recommend you spend a couple of hours watching “Fat, Sick, and Nearly Dead.” It’s a documentary and it is available on Netflix.

  8. R says:

    I am sorry but Fat, Sick and nearly dead was just vegan propaganda riddled with misinformation and half-truths. Sugar is not inherently fattening, it has everything to do with the quantity of consumption. A diet high in fruit will not be overly fattening due to the water volume and fiber content being very satiating. Fruit does not have the hyperpalatability of today’s junk food, making it hard to overeat before the brain receives the chemical messengers letting it know the body is full.

  9. R says:

    A good start would be a sugar-sweetened beverage tax.

  10. David says:

    Regarding your footnote, I have observed local people in the tropics who eat very healthy diets, local fruits and vegetables with very little meat and not even too much fish. In many places, the prevalence of obesity is quite high. So maybe the hypothesis that naturally sweet fruits also can cause obesity is true.

  11. Tom says:

    On “sweet” fruits found tin the tropics —

    First, many tropical areas, such as Polynesia, were settled by humans at most 50,000 years ago, which is still relatively recent in evolutionary terms. Homo sapiens and its forerunners had been evolving in and around Africa for millions of years.

    Second, the sweetness of the fruits may be a recent phenomenon as well, as farmers with sweet tooths (sweet teeth?) learned to cultivate sweeter and sweeter fruit.

  12. readerOfTeaLeaves says:

    Excellent, long article in the Guardian about the roots of the obesity epidemic in shifts within the food industry back in the Nixon era:

    Money quote:

    “Anne Milton, the [UK] minister for public health, tells me that legislation against the food industry isn’t being ruled out, because of the escalating costs to the NHS. Previous governments have always taken the route of partnership. Why? Because the food industry provides hundreds of thousands of jobs and billions in revenue. It is immensely powerful, and any politician who takes it on does so at their peril. “Let’s get one thing straight,” Milton tells me, however. “I am not scared of the food industry.”

    And I believe her, because now, there is something far bigger to be frightened of. Eventually, the point will be reached when the cost to the NHS of obesity, which is now £5bn a year, outweighs the revenue from the UK snacks and confectionery market, which is currently approximately £8bn a year. Then the solution to obesity will become very simple.”

    In the US, I’m not aware of a solid, comprehensive summary of the total costs of obesity (lost productivity, higher insurance premiums, enormous profits for diabetes meds, etc, etc).
    Where is our Anne Milton?
    She seems to be making a simple, clear argument in favor of public health.