Previous Philosophical Transactions:

• JP Callaghan on Lithium Pharmacokinetics
• Lithium in Scottish Drinking Water with Al Hatfield
• M’s Experience with Potatoes-by-Default
• Jon on One Year Post-Potato-Diet
• Neoncube on The Meat and Veggies Diet

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Hi SMTM,

I’ve now had the pleasure of watching many people encounter A Chemical Hunger for the first time. Some of them get wide-eyed with wonder, and some of them make the same expression that babies make when they taste lemon juice.

Those with the lemony reactions are always certain they know why the obesity epidemic happened. Often, their explanation is something like this:

We have an obesity epidemic because food became more enticing and so people eat more of it. It’s tastier, more available, more varied, more indulgent, etc. We live in a world where you can get hot salty french fries anytime, anywhere, and that’s why we’re fatter than our forefathers.

Let’s call this the McDonald’s Hypothesis. I understand the appeal of this theory because I believed it myself. It conjures up images of, say, spindly 1930s Dust Bowl migrants sipping thin stew to stave off starvation, juxtaposed with portly 2020s Americans horking down chicken McNuggets. When you put it like that, the obesity epidemic seems to make perfect sense.

But that’s not actually the comparison that needs explaining. The obesity epidemic isn’t something that happened, it’s happening. It started pretty suddenly in the 1980s, and it hasn’t stopped since. As you point out, not only did obesity increase from 2000 to 2008, but it increased faster between 2010 and 2018. For the McDonald’s hypothesis to be true, people would have to start horking down chicken McNuggets starting in 1980, they’d have to hork more nuggets every single year since then, and their nugget-horking rate would have to be increasing in recent years.

Now my intuitions are all screwed up, because that doesn’t seem true at all. Extremely tasty food was already omnipresent when I was a kid, and it doesn’t seem to have gotten tastier or more omnipresent since then. I especially don’t get the sense that food was tastier in 2018 than it was in 2015. There was already a McDonald’s in the next town over, and it’s not like they’ve opened five more since then. In fact, McDonald’s predates the obesity epidemic by decades, and the number of franchises in the US has declined slightly in recent years.

Or think of it this way: is the food in the supermarket more enticing now than it was five, ten, twenty years ago? If anything, it seems easier to get “healthy” stuff, as well as local and organic food, as this article confirms. (It also mentions a new trend of smaller grocery stores that provide less variety.) But the McDonald’s hypothesis would predict the opposite––more and more foods so enticing that I can’t help but gulp them down.

Here’s one notable example where food has gotten demonstrably less tasty. McDonald’s used to make their fries in beef tallow, which was apparently delicious. Then a rich guy named Phil Sokolof had a heart attack, blamed McDonald’s fries, and launched a $15 million campaign against them. McDonald’s caved and replaced the beef tallow with vegetable oil in 1990, and then switched the oil again in 2007 to eliminate trans fats. Malcolm Gladwell famously pines for the original fries: 

When I was a teenager and I went to McDonald’s all the time, I went there because of the fries. And then at a certain point, the fries didn’t taste the same. They sucked. I go back there now and they’re not the fries I grew up on.

[…]

What I do in the show is I go to the leading food research and development house in the country—place called Mattson—and I had them … do a taste test. And they made french fries just like McDonald’s would. The old-fashioned way using beef tallow, and then they made a precise replica of the modern fries, and we did a blind taste test. It’s no contest. I mean, it’s like you’re eating two completely different foodstuffs. It’s phenomenal. It blows my mind that McDonald’s would do this. So they know it better than anyone what they had to give up when they shifted from beef tallow. They were throwing away the franchise. And they must have done taste tests. And they must have said, “Oh my God, we’re taking something that’s an A+ and we’re taking it down to a B-, and even though our brand and our livelihood depends on this food item, we’re going to throw it away.”

This isn’t conclusive or anything. The point is that the McDonald’s Hypothesis seems obvious at first, and then it seems way less obvious as soon as I have to compare it to the actual facts that need explaining.

The natural fallback position from the McDonald’s Hypothesis is the Something in Food Hypothesis. In this theory, it’s not that food is tastier, or more abundant, or varied, or anything like that. It’s that there’s Something in Food now that wasn’t there before, something that’s making us fatter. McDonald’s french fry oil now tastes worse, but maybe it screws with your weight through some other mechanism. Anyone who retreats from the McDonald’s Hypothesis to the Something in Food Hypothesis should notice that they’re now in the neighborhood of the theories in A Chemical Hunger that seemed so ridiculous mere moments ago.

Another common backup theory is the Couch Potato Hypothesis: people are getting fatter because they move around less. But again, why did they suddenly start doing that in 1980, and move around less every single year since then? Why was that the year of The Great Sitting Down? Why didn’t it happen in 1953 when the majority of Americans got a TV, or in 1960 when the majority of Americans got a car, or in 2000 when the majority of Americans got a computer and started using the internet, or in 2013 when the majority of Americans got smartphones? Why is it happening faster in recent years? I guess TikTok and Netflix could be improving their algorithms every year and getting you to sit still for longer, but is that really a bigger deal than getting a car or a computer in the first place? And remember, this is adult obesity we’re talking about. Did 45-year-olds move around less this year than they did last year? With even 30 seconds of reflection, the Couch Potato Hypothesis starts to seem a little ***half baked***.

A situation like this is a good test of your epistemic immune system. If you’ve never really thought about the causes of the obesity epidemic and your immediate reaction to a new explanation is “NO WAY, IMPOSSIBLE, REJECT, I ALREADY KNOW THIS ONE,” your mental t-cells are probably too active. That doesn’t mean the new explanation is right, just that it’s a little silly to scrunch up your face at it.

The solution isn’t to be more gullible. The world is full of crazy people saying crazy things; we’re right to be skeptical. In fact, the solution is to be more skeptical, and to direct a healthy dose of that skepticism toward your own thoughts, because that’s the only way to realize when your certainty-to-evidence ratio is out of whack.

Most of my beliefs are unconsidered and unsupported. I’m not ashamed of that––who’s got the time to consider and support every single thing they think? I scrutinize the few things I care about and make my best guess on the rest. Every time I see someone react to a new hypothesis like they’ve just tasted lemon juice, it’s a helpful reminder that I need to file my guesses under “Guesses” and not under “EXTREMELY CERTAIN AND WELL-KNOWN THINGS THAT I KNOW.”

~*~*~*little is known, but much is believed*~*~*~

Sincerely,
Adam