This post has been recorded as part of the LessWrong Curated Podcast, and can be listened to on Spotify, Apple Podcasts, Libsyn, and more.

A Chemical Hunger (a), a series by the authors of the blog Slime Mold Time Mold (SMTM) that has been received positively on LessWrong, argues that the obesity epidemic is entirely caused (a) by environmental contaminants. The authors’ top suspect is lithium (a)^[1], primarily because it is known to cause weight gain at the doses used to treat bipolar disorder.

After doing some research, however, I found that it is not plausible that lithium plays a major role in the obesity epidemic, and that a lot of the claims the SMTM authors make about the topic are misleading, flat-out wrong, or based on extremely cherry-picked evidence. I have the impression that reading what they have to say about this often leaves the reader with a worse model of reality than they started with, and I’ll explain why I have that impression in this post.

(Preamble) A brief summary of their hypotheses

The SMTM authors have recently (a) summarized their hypotheses on how lithium exposure could explain the obesity epidemic. The first hypothesis is that trace exposure is responsible:

One possibility is that small amounts of lithium are enough to cause obesity, at least with daily exposure.

And the second one is that people are intermittently exposed to therapeutic doses:

[E]ven if people aren’t getting that much lithium on average, if they sometimes get huge doses, that could be enough to drive their lipostat upward.

I am going to argue that neither of those is plausible. I address the plausibility of the second hypothesis in the next section, and the plausibility of the first one in the rest of the post.

Lithium exposure in the general population is extremely low, even at the tails, in the majority of countries for which we have data

A few days ago, the SMTM authors published a literature review (a) on the lithium content of food. They conclude that, whereas the existing literature isn’t great, “[i]t seems like most people get at least 1 mg [of lithium] a day from their food, and on many days, there’s a good chance you’ll get more.” They also say it seems plausible that people are intermittently exposed to doses of lithium within the therapeutic range through their diet.

However, their literature review prett...