Diet Soda: The Devil's Work

I drink a lot of diet soda.  Well, probably around 2-3 cans a day.  So my ears perk up whenever I hear anyone propose that it is unhealthy.  For some reason, there is something about diet soda that really bothers people.  Given the high levels of skepticism in the general public, despite the fact that not only have millions of people have been drinking it for decades and no good evidence that it causes real harm, I'm suspicious there might be something deeper going on.  Diet soda can actually be harmful to your teeth, because it contains citric acid, which corrodes enamel.  But no more so than anything else containing citric acid, and can be controlled by drinking with food, so that salivary glands are stimulated, restoring the mouth's natural pH.

But no, the real skepticism isn't about tooth enamel.  It is mainly about cancer.  The biggest fear is the artificial sweeteners used.  Some have a vague notion that the carbonation is dangerous, something about CO2 is seemingly problematic.  However, considering it is a naturally occurring byproduct of human cellular respiration and therefor critical to our survival, I'm not sure they really understand what it is. 

The cancer concerns have a kernel of truth to them.  A derivative of coal, it didn't take long after its discovery for people to worry over its safety.  A reasonable enough suspicion, however coal itself is indeed a "natural", quite literally "organic" substance.  In 1906, when Roosevelt was promoting saccharin as a healthy alternative to sugar as part of his fitness promotion, vice president Sherman begged him to avoid it, calling it "a coal tar product totally devoid of food value and extremely injurious to health."  Despite further studies over the following decades showing it to be harmless, suspicions held.  In the 1970's, rats were found to have developed bladder cancer after being exposed to saccharin, leading to attempts by the USDA to ban it.  However the findings were controversial, and eventually in 2000, it was discovered that rodent biology was actually quite different from humans in that their bladders had very different metabolic reactions to certain substances.

Comparing biological reactions across species is always tricky (as is cancer epidemiology in general).  I happened to find a fascinating demonstration of this on the website of the Carcinogenic Potency Project, until recently headed by a highly respected cancer researcher.  The basic point is that almost anything can be poisonous, or even carcinogenic at the right doses.  No where is this more true than with rodent population.  Essentially, if one were to go by cancer rates in rodent exposure, we would need to ban everything from coffee to lettuce to hamburger meat.  By the way, highest on the list of rodent-cancer causing "natural" chemicals?  Symphytine, naturally found in comfrey root.

There are probably many reasons why people cling to suspicions about artificial sweeteners.  The idea of anything "artificial" seems worrisome to many (even though plenty of "natural" chemicals are extremely deadly, and synthetic chemicals are just as safe as naturally occurring ones.  Many people have a basic mistrust of science in general, worried that they are being manipulated by industry.  This is always a real concern, but one easily overcome by simply looking at where the study came from.  If mainstream, respected institutions staffed by authoritative, published and peer-reviewed experts are then distrusted, well, we're off into conspiracy land and the epistemological loop is closed anyway.

My own favorite theory is that many people don't like diet sodas simply for the unconscious, puritanical intuition that is suspicious of enjoyment for enjoyment's sake, and especially if one has not earned it.  Unlike regular sweets, which are high in calories which must be paid for either through exercise or self-denial, diet sodas are essentially "free" happiness.  And any deserving soul can't possibly have that without making a deal with the devil - paid for in cancerous tumors no doubt...