Friday, August 07, 2009
Image by ingorrr.
An interesting article was published earlier this week on the website of the journal Medical Hypotheses, suggesting that the current obesity epidemic may be caused by salt addiction. The article is provocatively titled "Salted Food Addiction Hypothesis may explain overeating and the obesity epidemic" and as you might expect given the journal that published it, it is wildly speculative. Now I'm just going to say this upfront - I think the authors are probably wrong. But it can be fun to speculate, and I did learn some interesting things from the paper, so I think it could make for some interesting discussion.
The authors do their best to build a case that people can become addicted to salt. Despite my original expectations, the study was quite a challenging read, so I will do my best to summarize what I felt were their main points:
1. Once people are exposed to sodium, they tend to crave more of it.
2. Our current environment exposes us to very large amounts of sodium.
3. Once people become "addicted" to sodium, they are likely to seek out ever increasing amounts, which will almost certainly mean an ever increasing caloric intake.
The authors suggest that dietary sodium may affect reward centers in the brain, just like other addictive behaviors. Or, as they put it:
‘‘Salted food craving” may be a neuropsychiatric manifestation of severe dysphoria resulting from a high tolerance and severe withdrawal at mu-s opioid receptor sites, while overeating may be a neuropsychiatrically based maladaptive attempt to self-medicate mood destabilization.
In other words, salt intake may affect opiate receptors, just like certain drugs. To test this theory, the authors performed a truly novel experiment - they examined whether people going through opiate withdrawal increased their intake of salty food. Unfortunately, as far as I can tell they didn't actually measure salt intake, which seems like a bit of an oversight. As you might expect, this is where the paper goes seriously off the tracks. While going through opiate withdrawal, subjects gained an average of 11 lbs, and self-reported that they increased their intake of fast food. How much more fast food did they consume? They don't say, nor do they provide any statistics. Luckily, the authors don't let this stop them from interpreting their findings! Since fast food tends to be high in sodium, the authors interpret this anecdotal increase in fast food intake to suggest that the subjects were trying to self-medicate their opiate deficiency by consuming higher amounts of sodium. WHAT???
This is one of the best examples of over-interpretation that I've ever seen. It is unclear if there was any measure of the primary outcome (sodium consumption), and their proxy (fast food intake) was self-reported. What's more, we have no information on how the self-report was done, or even basic statistics. It's almost too bad that they included the "experimental" data in the paper, because the hypothesis they put forward in the first half of their paper is interesting and at least somewhat plausible, but this "experiment" is so strange that it leaves a bad (and somewhat salty) taste in my mouth.
So what's the take-home message? Most of us consume far too much sodium, which is almost certainly bad for our health and longevity. Is it behind the obesity epidemic? Almost certainly not.
Cocores, J., & Gold, M. (2009). The Salted Food Addiction Hypothesis may explain overeating and the obesity epidemic Medical Hypotheses DOI: 10.1016/j.mehy.2009.06.049
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