Carcinogens in natural foods - the Ames test

I have previously written about the difference between natural foods and "unnatural foods" in terms of how much carcinogens they contain. I did one post on "Irrational fear of pesticides", and another post that I called "natural foods contain more carcinogens than unnatural foods".

Just now I found a video clip from Physics for Future Presidents, a UC Berkeley lecture series that you can watch for free online, in which Richard Muller, an entertaining physicist explains what this is all about. Watch and enjoy.

Irrational fear 1: Pesticides

About three months ago I wrote a post on natural foods and the highly exaggerated danger associated with pesticides. I cited research done by Bruce Ames (see picture), Professor of biochemistry and molecular biology at UC Berkeley. In this very interesting interview, Bruce Ames gives his view on organic foods. In the following excerpt from this interview Ames explains that the reason why he is against spending more resources on natural foods is not that it contains more carcinogens but rather that the production and in consequence also the products is more expensive. More expensive fruits and vegetables means less consumption which will result in more cancers:

Ames: Yes. I'm much more interested in preventing cancer. Then we have to get out to the public what's important. If you tell them about trivia all the time, they get completely confused, and it's counterproductive. I just think all this business of organic food is nonsense basically. We should be eating more fruits and vegetables, so the main way to do that is to make them cheaper. Anything that makes fruits and vegetables more expensive may increase cancer.

When I cite this information people often ask where Bruce Ames gets his money from. Is he really trustworthy? This is a fair question when you take into account the fact that the food industry is a big industry, and if organic foods would suddenly become the public choice it would certainly be rather detrimental to many companies. What many people seem to forget though is that producers of organic foods also have money waiting for them, should they manage to sway the public opinion. Unless it is suggested that organic food producers have a superior morality, immune to economic incentives, this is not a valid argument, after all the economic incentive is there for both sides. Maybe those the people who tell us that organic is the way to go do so because they would get rich if people followed their advice?

I feel quite confident that Bruce Ames is not bought by the food industry. Why? Partially, I believe Ames is a good guy because of what my intuition tells me. When I read the interview (referenced above) with this scientist he just doesn't strike me as a man who has sold his soul to the devil, quite the contrary in fact. However, the main reason why I don't think Ames is bought by the food industry is that he is also the man who first proved that many synthetic pesticides are carcinogenic. For quite a while he was a hero to all the natural food proponents.

Bruce Ames showed that indeed many man made chemicals are carcinogenic, but what reason do we have to assume that natural pesticides aren't also carcinogenic? Ames did not make this assumption and when he tested natural pesticides, which are created by the plants themselves as a protection, he found that pretty much the same proportion of natural pesticides was carcinogenic. Furthermore, Ames discovered that plants which are not treated with synthetic pesticides (i.e. natural foods) contain more potent carcinogens than plants which have been treated with pesticides. (Things can be more or less carcinogenic; for example, even though mushrooms contain 50% carcinogens they are very weak and therefore doesn't do a lot of damage whereas coffee contains much stronger carcinogens.) Read my previous post if you want to understand why. Add to this that 99.9% of the pesticides that we ingest are natural pesticides and you will understand why this post is about irrational fear.

Here we are worrying about 0.1% of the pesticides we ingest which according to the data are, if anything, less mutagenic than the other 99.9%. That is what I would call irrational fear…

”Natural Foods” contain more carcinogens than ”Unnatural Foods”

If you are like me, the first thing you will react to in the headline is my discrimination between natural and unnatural foods. It is my impression that people who call natural foods "natural foods" refer to foods which have not been treated with pesticides. Personally I don't think this makes them more natural, and it definitely does not necessarily make them better. I suppose that natural foods are more natural in the sense that it is what we used to eat back in the days when we did not have the kind of technology that we have today, though based on that one could argue that primitive foods would be a more appropriate label. I must admit that I have never actually heard anyone talk about unnatural foods, I just assume that if someone asserts that foods which have not been treated with pesticides are natural, then they must think that foods which have been sprayed with pesticides must somehow be unnatural.

In any case, people who eat natural foods often claim that it is better for you. Why? Well according to the people I have talked to, natural foods are less toxic to you because they have not been sprayed with pesticides. Pesticides, according to these people are quite poisonous and ingesting them will result in all kinds of bad effects such as cancer. Therefore natural foods, which have not been sprayed with any pesticides must be better for you. The problem is that all foods, including natural foods, produce their own pesticides. In a moment I will argue (convincingly I hope), that natural foods in fact have a larger concentration of pesticides and that the pesticides in natural foods are even more toxic than the synthetic pesticides that we produce and spray on our "unnatural foods".

So how come natural foods have pesticides in them? If you think about it the answer is quite obvious. All plants need defenses against plant eaters. If a plant cannot avoid predation, then natural selection will take care of that plant in no time. That is, any plant without defenses will die and only the ones that do have a proper defense will be able to survive, reproduce, and thus send their genes into the next generation. Now plants are not particularly mobile, and therefore they cannot run away from their predators. So what do they do? They evolve defenses which either makes them hard to eat (e.g. thorns on cactuses), or they evolve chemical or pesticides that will either kill or hurt the predator when they try eating the plant. These substances are called natural pesticides. Natural pesticides are the chemicals contained within plants in order to make organisms that eat them sick or even kill them.

So we have two types of pesticides. There are pesticides that we produce in our industries and spray on plants to protect them from other organisms, and there are pesticides that the plants make themselves for the very same reason. What is the difference between these two types of pesticides? You may be thinking that since we have been exposed to natural pesticides (the ones the plants make) for a longer time, we would be able to handle them better, not so. The defenses we have in our body to protect us from pesticides are general, that is they don't care whether it is a natural pesticide or a synthetic pesticide, in fact they treat almost all different pesticides the same way. Throughout our evolutionary history, as we have included more things in our diet, we been exposed to new "natural pesticides". To our body the synthetic pesticides that we spray on plants are simply yet another novel pesticide. If you are still not convinced, consider the fact that there are quite a few types of pesticides that we have been exposed to for thousands and thousands of years which still today can be very bad for us.

I hope to have established that there is no general qualitative difference between the pesticides that we produce in our industries and the pesticides that plants produce. However, in all fairness this is not entirely true. The synthetic pesticides that we use today are selected based on their ability protect the plants on which they are sprayed, and importantly only mild toxins are used, that is our body can take care of them relatively easily. This means that if a plant is sprayed with synthetic pesticides that plant doesn't need to make its own pesticides because it is already protected. Of course, to the extent that the synthetic pesticide is toxic, the plant will also become more toxic, but normally this effect is very small. Now if, on the other hand, you do not spray a plant, then that plant will have to form its own pesticides, and the stronger the better. The plants that do not do this, as I mentioned before, will die. In consequence, each new generation of natural food crops will be the offspring of the most toxic plants in the previous generation. This should logically mean that the natural pesticides in natural foods are much more toxic than the natural pesticides in foods that have been sprayed.

This question has in fact been tested experimentally by Bruce Ames at the University of California, Berkeley. How did he test this? Well first, being a cruel scientist, he created a bacteria that lacked an enzyme that was critical for its survival. The only way for the bacteria to survive was if it, through random mutations got a working gene capable of producing the vital enzyme. Now, Ames would create say a thousand colonies of these unfortunate bacteria. Then he would squirt something, say a natural pesticide, on all the different colonies and see how many would grow. Ames could infer that if a bacterial colony would start growing then mutations had occurred in that colony, in other words the substance squirted on them must have been mutagenic and therefore carcinogenic. If you compare natural pesticides and synthetic pesticides in this type of test you will see that the natural pesticides will leave much more survivors than the synthetic ones. This may be good news for the bacteria, but not for us, because more mutations means higher risk of cancer. In other words the predictions stated above has been confirmed in the experiments performed by Ames.

What do I want to say with this? Well, I do not want to give the impression that I think natural foods are necessarily bad. Doing a very quick literary review I found a few studies claiming that there are more nutrients in organic relative to normal foods (organic foods is an extreme form of natural foods). However, all I want to say is that I think that our fear of synthetic pesticides is probably a little bit exaggerated, and that in many cases the toxins produced by the plants themselves are far worse.

Ps: For a good chapter on carcinogens in foods see Ames here in Handbook of toxicology