Mutagens on the menu

If you’re the sort of person who enjoys starting arguments, the topic of food safety is your ever-faithful friend. Everyone eats, and everyone has an opinion about what they eat and about all that weird stuff that other people are willing to put in their mouths. You’d think that the principle of de gustibus non disputandum est (there’s no accounting for taste) would forestall a lot of the wrangling, but look around you. There’s certainly a difference between arguing about matters of taste and matters of health and safety, but drawing an exact line between those is tricky.

Every so often, some portion of the internet ignites with a list of evil, toxic food additives that (gasp!) you didn’t even know you were eating (number seven will surprise you!). While writing a chemistry blog, I’ve inevitably become involved in some of these over the years, and I’ve come to think that a lot of this comes down to (first) the ancient belief in vitalism and (second) the even more ancient reflex of disgust.

Put crudely, the vitalism part is the division that people make (to varying degrees, and perhaps even unconsciously) between industrial chemicals that come out of fuming vats and the healthful, natural foods that our ancestors just instinctively reached for in the bounty that lay all around them. But this categorisation scheme doesn’t have as much to recommend it as you might believe. I’ve had some vigorous and rather complex email exchanges, for example, with people who have managed to convince themselves that benzoic acid (as found in many fruits) is a perfectly safe and natural thing to be eating, while sodium benzoate is a toxic preservative used by the industrial food complex to poison us all. Think about that one for a moment. I have also had people try to convince me that pure vitamin C as isolated from fruits and vegetables is completely different from vitamin C made by organic synthesis (and no, they weren’t talking about chiral centres or polymorphs, believe me). Reminding folks that strychnine and botulinum toxin are all-natural is always enjoyable, too, but after a while you wonder if you’re getting through to anyone.

And the disgust part is a fundamental human reflex that is widely taken advantage of to drive readership and advertising revenue: ‘Did you know that your breakfast cereal has a chemical in it that’s also used to make flameproof underwear?’ OK, I made that one up, but you get the idea. It’s closely related to advice to never eat anything with ingredients that you can’t pronounce, but that one breaks down quickly when you start looking at systematic names for, say, vitamins.

Bruce Ames famously said that he considered pesticides to be net anticancer compounds, because they made more fresh fruit and vegetables available to more people

Of course there are potentially harmful chemicals in foods. The thing is, a great number of those are part of the food itself, not additives tossed in by someone wearing a respirator and an orange jumpsuit. Fresh-squeezed broccoli juice has plenty of its own mutagenic compounds in it, as do mushrooms, carrots, liquorice and many other foodstuffs. At the same time, all these fresh fruits and vegetables have plenty of beneficial substances in them, so the only real answer to a question such as ‘Does broccoli have mutagens in it or compounds that protect against mutagens?’ is ‘Yes’.

Bruce Ames (of mutagen-detecting Ames test fame) wrote a number of papers about this phenomenon, and concluded that our digestive tracts and livers had evolved to deal with a huge variety of compounds, and could safely handle the vast majority of those. He noted that there’s no real difference between mutagenicity when you compare collections of natural products with collections of man-made ones, and suggested that we should spend more time and effort on the (much shorter) list of things that are known to cause trouble rather than setting off alarms about parts-per-billion levels. That doesn’t mean that we shouldn’t keep looking for new things to add to that list – especially those that might actually be capable of effects in such concentrations – just that we shouldn’t expect to find many of them.

Which we haven’t. Ames famously said that he considered pesticides to be net anticancer compounds, because they made more fresh fruit and vegetables available to more people. You may not be willing to go that far, but it’s worth thinking about how much you agree or disagree with that point, and why…