Why are Americans so fat? A radical group of online scientists has a theory

I first encountered the Twitter account “Slime Mold Time Mold” after seeing a viral thread about the chemical causes of the American obesity epidemic. The next thing I knew, the people behind the account were running experiments around “all-potato” diets — I even had friends who participated in them. Seriously, friends who bought pounds of potatoes a week and even ate them, all because of a research project they learned about on Twitter.

SMTM is nothing if not a cultic figure in a certain corner of the web. But what exactly are they? Who are they? Is it all a big performance, or are they DIY scientists? Or are they institutional scientists hiding behind an anonymous account? I reached out to them to learn more … though, you might be left with more questions than answers.

Katherine: What is “Slime Mold Time Mold”? Who’s behind it?

SMTM: We are mad scientists who are gathering in the spaceship MOLD TIME. We will play freely without fear of risky things. They must create new dreams and findings by breaking traditional styles.

Katherine: Very Parliament. You were put on my radar thanks to your viral thread about the mysteries of obesity. For people who aren’t already familiar with that thread, what are the eight mysteries?

SMTM: The first mystery is the epidemic itself. For most of history, the obesity rate was about 1% to 3%, even when people had all the food they wanted. Today, many countries have a 40% obesity rate or higher. Even in “lean” countries like Italy, France, and Sweden, the obesity rate is around 20%.

The second mystery is how quickly the shift occurred. In 1975, there wasn’t a single country on earth with an obesity rate higher than 15%.

The third mystery is that obesity rates haven’t stopped climbing since 1980 and show no sign of slowing down. Obesity in the U.S. increased more than twice as much between 2010 and 2018 than it did between 2000 and 2008. After 40 years, this seems normal, but historically it is bizarre.

Mystery four is that hunter-gatherers almost never become obese. Different hunter-gatherer groups eat very different diets. Some have diets that are extremely varied. Some survive largely off just two or three foods. But they almost never become obese or even overweight. This can’t be explained by the amount of food available or by physical activity, because many groups have more food than they can eat and partake in very little exercise.

Mystery five is that zoo animals, domestic pets, and wild animals are becoming more obese as well. This can’t be the result of changes in their diets, because lab animals live in contained environments with highly controlled diets and are also becoming more obese. Even wild deer seem to be getting fatter and fatter.

Mystery six is that there seems to be something especially fattening about processed human foods. Animals quickly become overweight on a diet of human snack foods but tend to remain lean on a diet of animal chow, even when the chow is also high in fat and nutritionally matched.

Mystery seven is that people who live at higher altitudes have lower rates of obesity. Colorado is the highest-altitude U.S. state and has the lowest rate of obesity. Mississippi has the highest rate of obesity and is only a few hundred feet above sea level. This isn’t limited to the U.S. — we see the same altitude-obesity relationship in countries like China, Spain, Tibet, and Iran.

Mystery eight is that diets don’t cause reliable weight loss. This has been demonstrated repeatedly in different meta-analyses published over the last decade. On pretty much every diet, people lose a little weight at first but gain most of that weight back within a year. Though the jury’s still out on the potato diet; we have to wait another year to see if people keep the weight off since we just got the first results.

These are the eight mysteries we described in Part I of our series "A Chemical Hunger," and you can check out that post for more detail on all eight. There are also two more mysteries that we would have included if we had written the series today.

Mystery nine is that some countries are much more obese than others, and no one knows why. The most obese countries in the world are all tiny island nations in the South Pacific, some of them with obesity rates of more than 50%. The most obese region in the world isn’t North America; it’s the Middle East, where most countries have obesity rates above 30%. Kuwait is more obese than the United States and has been for a long time. There are a lot of weird patterns like this.

Finally, mystery ten is that different professions have very different rates of obesity. Truck drivers, firefighters, mechanics, and some health care professions are much more obese than average. Surveyors, designers, researchers, and a whole different set of health care professions are much less obese than average. This doesn’t have to do with class or income level — research by the CDC consistently finds little or no relationship between obesity and income.

Katherine: What inspired that thread? How did you vet what you found?

SMTM: We’re detectives. We noticed a bunch of mysteries and figured we should write about them, and then it got a little out of control. Next thing we knew, we had several thousand words on the subject. Whoops.

We vetted what we found by reading primary sources and using our brains. We also emailed some of the authors of the papers we read to get more detail. And we asked our smart friends what they thought. Then we put it on the internet and saw what people on the internet said. Hey, it worked for Linux.

Katherine: Why do you think some people aren’t susceptible to obesity?

SMTM: It seems clear that the differences are largely genetic. Twin studies, for example, point clearly to genetic differences. We think this explains most of why some people are susceptible to obesity and others aren’t.

Beyond that, there are geographic differences — people living in Colorado are going to be less susceptible than people living in Mississippi, and people living in Thailand will be less susceptible than people living in Kuwait. So far no one has done an experiment to show that this geographic relationship is causal, but there are a lot of anecdotes that suggest it is.

It also looks like there are some big by-profession differences. Something about being a truck driver or a mechanic seems to make you much more susceptible to obesity. It might be something about working around vehicles or heavy machinery since transportation workers are also unusually obese.

Katherine: What is the least satisfying explanation for obesity? What about the most?

SMTM: Willpower is the least satisfying common explanation in our opinion.

There are real differences in willpower between individuals, but it’s not like everyone’s willpower started suddenly getting worse 50 years ago or that people have astronomically less willpower in Kuwait than they do in Thailand. People in the 1920s had ice cream and “lard-based diets”; there were plenty of calories around, but very few people got obese.

In the words of Stephen Guyenet, “This model seems to exist mostly to make lean people feel smug since it attributes their leanness entirely to wise voluntary decisions and a strong character. I think at this point, few people in the research world believe the CICO model.”

We think the contamination hypothesis is the most satisfying explanation so far, though the jury is still out on what contaminant or contaminants are responsible. Of the contaminants we’ve considered, right now we think there’s the most evidence for lithium. But that doesn’t mean we’ve dismissed other contaminants. It really might be more than one — for example, we’re currently doing some analysis of publicly available CDC data to see if we can find more evidence for or against PFAS.

Katherine: I’ve always thought that the “threat” of body positivity is overblown — it’s for people who are already obese — but many people on the center and rightwards think that it perpetuates obesity, as opposed to validating existing life choices. Do you have any strong opinions on the role culture plays?

SMTM: Culture is all about signals. When the environment changes, things become easier or harder, or they take on a new context and new meaning, and that changes culture.

When being low-class meant working in the field and it was hard to keep your skin fair, having fair skin was a good way to convey that you were upper-class. When fabric was expensive, styles with pleats, trains, and many layers were a good way to convey that you were rich. Now that fabric is cheap and poor people work in dimly lit warehouses (to a first approximation), high-class and wealthy people must find new ways to show off.

Things that encourage people to move to Kuwait or get jobs as truck drivers may perpetuate obesity. Other than that, we’re not sure culture plays any role at all. If anything, obesity perpetuates weird cultural stuff. We’ve tried shaming people about obesity for the last couple of decades and it clearly doesn’t work, not to mention that it’s mean. We think it’s most important to be excellent to each other.

Katherine: Why do you think obesity is such a sensitive topic these days?

SMTM: Is it? People like having control over their health and appearance.

Katherine: For people who read your thread and might be scared — how can they protect themselves from contaminants?

SMTM: Honestly, there's not much you can do. We discuss this at some length in Part X of our series. The best advice we can give is: No grocery store sheet cakes. Seriously, who knows what’s in those things? Or we do know, and trust us, you don’t want to know. Don’t eat them.

Besides this, there are a few things. You can change professions, since some professions are much heavier than others. You can move to a less obese region, like Colorado, or a less obese country, like Thailand. If moving isn’t an option, you can spend a long vacation there; that might help. But these would only protect you against the contaminants that cause obesity (assuming contaminants cause obesity). If you move to Thailand, you may be getting exposed to more of other things.

You could also try eating more potatoes. We don’t know why the potato diet leads to so much weight loss, but it clearly does, at least in some people. Possibly it does something to clear your system of the contaminants that cause obesity. But if it’s not that, it’s something else.

Katherine: Are you black-pilled on fixing human food and water sources?

SMTM: No, we’re pretty optimistic. We fixed lead in our gasoline and figured out how to do public sanitation and stuff. We think that if we can pin down what contaminants are a problem, remediation will be pretty straightforward. It's not impossible; the worst part about these things is just that they take time, and it’s hard to figure out what’s going on in the first place.

The real problem is that there isn’t much effort being put into unknown problems. Water treatment engineers are on top of the known contaminants, but there aren’t many people focusing on figuring out if there are unknown contaminants we should be concerned about. When people do focus on unknown contaminants, progress seems to be easy. We’ve raised a bit of money to do some larger projects, which will be coming out in the next few months, but everything you’ve seen from us so far has been on a total budget of zero dollars.

It’s kind of like Thomas Kuhn’s distinction between paradigm shifts and what he called “normal science.” If we’re right, then this is a minor paradigm shift in obesity research. Paradigm shifts are hard. But once a paradigm shift is complete, you can pass the new paradigm off to normal science, filled with people who are exceedingly good at what Kuhn calls puzzle-solving — developing new techniques for measuring these compounds in food and water, detecting them in the human body, and removing them from the environment. This system already exists and is well geared to solve puzzles once people like us discover the right paradigm.

Katherine: What’s the potato diet? Why potatoes? What would you say to someone who thought you were crazy after reading that?

SMTM: The potato diet is a diet where you get most or even all of your calories from potatoes. Perhaps surprisingly, this is easy for many people to stick to, and people who stick to it for 28 days lose an average of 10.6 pounds. We decided to study it because there were a few really impressive case studies, and we figured it would be nice to have more data.

We would say: They’re right; we are crazy. They call it mad science for a reason.