Contra Slime Mold Time Mold on Obesity, Part 1: Background

I. What Are We Even Talking About?

Exhibit A:

Exhibit B:

AHHH THAT’S TERRIBLE WHY IS THAT HAPPENING???

II. The Scientific Consensus

There’s a trivial sense in which obesity is caused by simple physics. Energy flows into the body in the form of food, and out in the form of heat (mostly produced by normal metabolic processes, and a bit during exercise). If the flow of energy into the body exceeds the flow of energy out of the body, energy will be retained in the form of fat. This model is referred to as ‘calories in - calories out’. 

We know that calories in has increased since the mid-20th century, and calories out has stayed flat or maybe declined a bit. In a certain limited sense that does explain the obesity epidemic. But that explanation is too low-level to be useful, in the same way that “Deaths from gun violence are increasing because more energy from nitrocellulose explosions is being used to propel bullets at people” isn’t useful. We know people are eating more, but we don’t know why. 

The academic consensus right now is that obesity is caused by a dysfunction of the ‘lipostat’ - a system in the human body that regulates how much you want to eat. A thermostat will maintain a set temperature in a room, emitting heat when it gets too cold and pumping heat out when it gets too warm. Similarly, the lipostat maintains a certain level of adiposity in the human body. If you don’t have enough fat, your lipostat will cause you to eat more. If you have too much fat, the lipostat will cause you to eat less and to fidget and move around in order to burn calories. Something about our modern environment is setting our lipostats to high adiposity levels, which in turn is making us eat too much.

(It’s not super well understood what exactly the lipostat is, physically. The hormones leptin and ghrelin are involved, as well as certain brain regions, but the exact mechanism has not been fully mapped out yet.) 

But that just pushes the question up one level further. What about our environment is making the lipostat malfunction?

Stephan Guyenet, an actual scientist who’s spent his life studying this stuff, thinks it’s probably because modern food tastes too good. Industrially-produced food is optimized by capitalism to maximize palatability, and it makes sense that the outputs of that process would get tastier over time. If Guyenet is right, we’re eating more of them as a result. 

The original Lays chips were invented in 1940, but 40s grocery stores did not look like this.

III. Looking For Alternative Explanations

But there are good reasons to look for factors other than increased variety in the snack aisle. Everyone in the US has access to hyperpalatable processed foods, but poor people are fatter than rich people, and some ethnic groups are much more obese than others. There are also a bunch of things other than tasty foods that we know mess with the lipostat and cause long-term weight gain, including like half of all known medications and a few common infectious diseases, like Adenovirus 36 and maybe Toxoplasma gondii. 

Slime Mold Time Mold has an ongoing series about the causes of the obesity epidemic. They’re arguing that obesity is caused by chemical contamination. That’s entirely plausible, and worth exploring. But they’re making the case that the contamination is being spread via the water supply. The evidence they present for that is weaker than they think.

SMTM’s argument, laid out most clearly in this post, seems to hinge on two points:

1. SMTM claims that obesity is more common near river mouths and in endorheic basins than it is further upstream, and that this pattern can be explained by flowing water covering more distance and accumulating more contaminants.

2. Obesity is more common at lower altitudes than higher ones. Most published research on this subject claims that this is mediated by hypoxia, but SMTM claims that it’s instead a proxy for groundwater contamination.

In coming posts I’ll respond to each of these two points, explaining why I think SMTM’s arguments are unconvincing.

Why am I writing this? I really respect the work Slime Mold Time Mold is doing right now. They’re putting in serious work to improve our collective understanding of an important problem, and they might be making some real progress. But I think they’re wasting their time with this watershed thing, and probably leading others down a similar path. I hope this series steers them and their readers onto more productive research pathways.