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Welcome to The Nonlinear Library, where we use Text-to-Speech software to convert the best writing from the Rationalist and EA communities into audio. This is: It’s Probably Not Lithium, published by Natália Mendonça on June 28, 2022 on LessWrong. 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), 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 pretty much only includes studies that are outliers in the literature. Moreover, they use a misleading threshold for the therapeutic range of lithium. I’ll explain. The studies in SMTM’s literature review of lithium levels in food are pretty much all outliers In 2006, France conducted its second Total Diet Study (henceforth TDS). Across 1,319 food samples, the highest lithium concentration found was 0.6 mg/kg, in water. That’s not the highest average concentration among food groups – it’s the highest concentration of any single sample they tested. (For context, a standard clinical dose of elemental lithium is about 200 mg/day, or 1 gram/day of lithium carbonate.) Similarly, New Zealand’s 2016 TDS examined 1,056 food samples and the highest concentration it found in any single sample was 0.54 mg/kg (in mussels). Canada makes the raw data of its Total Diet Study publicly available (a), and they too measure the lithium content of their food. The maximum level reported is 1.1 mg/kg (in table salt, which is presumably rarely consumed in kilogram quantities) across 479 food samples, with the mean being 25 µg/kg and the median 11 µg/kg. Here’s a histogram of the data: Excluding table salt, the maximum value in the rest of the dataset (N = 476) is 0.4 mg/kg, in mineral water. Total Diet Studies in other countries report similarly low levels. Using data from the UK’s 1994 TDS (which included 400 food samples), the mean daily lithium intake among adults was estimated to be 17 µg/day, more than 50 times lower than SMTM’s estima...