Food alarmists, with all their shouting about toxic compounds in food, would be shocked if they actually knew something about food. Of course, if they continued learning, the shock would give way to the kind of calm that can only come with a true understanding. But what is the shocking revelation about our food that “they” don’t know?
Most Fruits and Vegetable Contain Naturally Occurring Toxins or Carcinogens
The truth is that most of the fruits and vegetables you eat contain at least one or two toxic or carcinogenic compounds. In his book Chemical Food Safety: A Scientist’s Perspective, author Jim E. Riviere reveals a few little-known facts about America’s most beloved fruit: the apple.
Apples and Cyanide
Some of my readers may know that the seeds of an apple contain doses of cyanide. It comes in the form of a cyanogenic glycoside known as amygdalin, which can break down into hydrogen cyanide, a well-known deadly poison. In fact, the Romans used cyanide preparations from apples or other fruits to execute people, or to murder them. Cyanogenic glycosides (linamarin in cassava is another) are one type of “cyanogen” found in plants—compounds that can break down to release free hydrogen cyanide. Cyanogenic glycosides represent about 90% of cyanogens.
Other fruits, you ask? Apple trees are actually part of the rose family, as are many of the fruits we eat. Cherry pits, apricot pits, and almonds also contain amygdalin. 1
Now, there is no real danger from apple seeds, even if you accidentally or intentionally swallow one. They have tough outer shells and they will pass right through your gut completely intact, able to sprout into, well, a crab apple tree of some kind. A crab apple is a small, extremely tart and astringent fruit that is pretty much inedible, but can sometimes be used for a good cider, or a preserve. To get an eating apple, you need to graft a cutting from the particular apple tree whose fruit you want to reproduce onto another root stock (you’d usually pick a known hardy root stock). The part that is up top is the part that would determine the kind of fruit. But, if you just throw some Granny Smith apple seeds into the ground, you would not get a Granny Smith Apple. That is right. Every single apple you eat needed a human hand to artificially propagate it. All apples are genetically modified.
But back to the cyanide. If you crush apple seeds, or chew them up, enzymatic hydrolysis of the cyanogens liberates hydrogen cyanide. Also, if you use a juicer, it is possible to release some of the cyanide. Once it enters your body, you are in big trouble!
Just kidding. Your body can safely detoxify these small amounts. Cyanide does not build up in the body. It is excreted. This does not mean it is a good idea to chew up apple seeds. Avoid, them.
Almonds and Cyanide
If you were paying strict attention, you may have paused when I mentioned almonds. We eat the “seed” of an almond, don’t we? Don’t worry. The almonds we eat are considered “sweet” almonds. It is the wild bitter almond which contains dangerous amounts of cyanogenic compound. They are, in fact, one of the best ways to get cyanide. They were such a concern that in the United States the USDA ordered all bitter almond trees to be destroyed. Have you ever heard that cyanide smells like almonds? Well, it is almonds that smell like cyanide, which is also responsible for the bitter taste. Bitter almond seeds contain up to 5% amygdalin, which is around 1 mg per seed. 10 to 15 bitter almonds is a lethal dose for a child. Adults can tolerate up to 50 or 60.
Domesticated sweet almonds contain much smaller amounts of amygdalin, although, due to the dominant gene mutation which produces this sweeter variety, some sweet almonds (around 2%) can end up containing larger amounts. A bitter taste would give this away. 2 3
Lima Beans and Cyanide
The familiar lima bean can also contain dangerous levels of cyanide. Fortunately, thorough cooking removes pretty much all the danger, and the lima beans we buy at the store are specially selected to contain less in the first place. However, some folds who grow lima beans in their garden may be growing varieties that contain loads of cyanide compound. As I mentioned above, there is also an enzyme present, which, when mixed with the compound, releases hydrogen cyanide gas. Fortunately, a time-tested way to render such foods harmless is to either grind them in advance, which releases the cyanide gas or to thoroughly soak and cook the beans. Still, in certain villages whose lima bean crops contain large amounts of cyanide, some crops, due to certain conditions, may contain even more cyanogens than usual, so that the usual methods aren’t enough, and entire villages get poisoned by cyanide. This is highly unusual, though.
So, when someone like Michael Pollan tells you should grow all your own vegetables so you’ll never ever have to worry, you can smirk knowingly and say “I think I’ll stick to my good old Green Giant or Hanover lima beans from the frozen case.” And this is coming from a guy who grew up eating lima beans straight from the fields (we froze and canned a lot of them too). The varieties of lima beans we use in the U.S. have a very low cyanide content, about 1 mg per 100 gram wet-weight. If a lethal dose of cyanide is .5mg per kilogram, a 70kg (154lbs) person would have to eat about 350 grams (0.7 lbs) of improperly prepared lima beans.
Cassava and Cyanide
Cassava also contains high levels of linamarin and lotaustralin, other cyanogenic glycosides. In some parts of Africa and South America, when people have little else to eat besides cassava, cyanide intoxication has occurred. No deaths have been reported, but this should show you that variety, when you can get it, is the safest way to eat. 4 Other examples are dhurrin in sorghum, and taxiphillin in unripe bamboo stems. 5
Apples and Carcinogenic Caffeic Acid
But back to the apple. Cyanogens in apple seeds aren’t the only problem. Apples also contain caffeic acid. That’s a known carcinogen! Oh, my.
Caffeic acid is all up in our food! It’s in spices, and many other fruits and vegetables besides apples, such as grapes, pears, carrots, lettuce, and potatoes.
Apples as a Chemical Cocktail
There are potentially other compounds of “concern” in apples. That is, if you are perverse enough to look at apples, or any other fruit, as a cocktail rather than a food. As I mentioned, Jim E. Rivere pointed out these potential carcinogens in apples, and made a salient point about how we view toxicity. I mentioned something similar in my previous post How Do We Know What Substances are Harmful?
People often assume that all it takes to determine the “toxicity” of a food is to determine what chemicals it contains, and then decide if one or more of these chemicals are toxic. However, a food can contain toxic chemicals and still not cause poisoning in humans or animals. First, the toxin must be present in large enough amounts. Second, it must be present in a form that can be taken up by the body and assimilated in some way. Some of the “toxic chemicals” that we are told to fear pass right through the gut unchanged, for example. Or, our body is able to safely detoxify small amounts of these chemicals.
Riviere asks that we imagine we are starting up a new biotechnology company. We decide we are going to synthesize an apple “from scratch.” In other words, we are going to build an apple in the lab. Before we could sell our engineered apple, we’d have to get approval. How would we do that? We’d have to identify all the chemical compounds that the apple contains and then individually test them for toxicity, using toxicology standards. But, let’s say we found no acutely toxic compounds. Could we sell our apples? No. We’d also have to give rats or mice huge amounts (I mean ridiculous gargantuan doses) of the compound to see if they got cancer. And guess what? We could be fairly certain that one or more of the compounds would be found to be ‘carcinogenic’ by this manner of testing. As Riviere also mentions, some of your rats would have died in the first place because of all the cyanide toxicity!
There is probably no way in hell you could get a synthesized apple approved, no matter how faithfully you reproduced the apple. And if you did, you’d have to attach all sorts of warnings to it. May be carcinogenic, contains toxic cyanogens. I’ve made my own version of Riviere’s mock apple label warning to make the point:
The author goes on summarize some comments from Bruce Ames, the biochemist responsible for the Ames test for chemical mutagenicity:
Bruce Ames is a California biochemist who invented the Ames test for chemical mutagenicity. Recently, he has been a prolific author on the relative risks of consuming natural versus synthetic chemicals. He has estimated that 99.9% of all pesticides in our diet are natural plant pesticides [pesticides the plants make to protect themselves] which occur in concentrations ranging in the parts per million category rather than in the parts per billion category, as seen with synthetic pesticides…trace levels of synthetic additives, which only may be suspected of being toxic in studies where animals as “megadosed,” are banned from the grocer’s shelves…It is conceivable that a manufacturer will be sued if these pesticides were found at violative levels in our food. Will I be taken to court because I feed my children cabbage or apples containing multiple natural carcinogens?…”natural: and “pesticide and additive free” implies that the the food is free from harmful chemicals and safer than produce grown without synthetic pesticides. However, the most potent chemicals are the natural components of both cabbage and apples. Is this policy correct or even ethical?
If you would like to read more perspective on this, I encourage you to get the book. 7
Plants Contain Natural Pesticides in Amounts Far Exceeding Synthetic Ones
Plants contain many chemical compounds that are natural pesticides. This helps protect the plant from pathogens, insects, or even animals. The concentration of these compounds in our diet have been estimated to be 10,000 times greater than synthetic compounds.
These compounds have not been scrutinized anywhere near as much as synthetic pesticides, but what we do know of them shows that in sufficient concentration, many of them could be quite harmful. There are countless examples of these chemicals. Celery, for example, causes contact dermatitis in workers who handle the celery, due to furocoumarin in the leaves and other parts of the plant. Celery as well, along with parsley, contains up to 30 parts per million of methoxypsoralen, which is a known rodent carcinogen. Limonene, found in amounts up to 40 parts per million in orange and mango juice is also a carcinogen. Potatoes, a member of the nightshade family, contain solanines and chaconine, especially if they are green (which can happen due to improper storage, etc.) We could go on and on.
Toxic Mold
We read lots of warnings about synthetic fungicides, most of which have been exhaustively studied for carcinogenic and mutagenic effects. What we don’t hear about is the many dangerous mycotoxins produced by pathogenic fungi that grow on plants, some of which are extremely carcinogenic, mutagenic, or toxic. Aflatoxins, which are produced by Aspergillus flavus are highly toxic to the liver, and in third-world countries have been connected to death from liver cancer. Penicillium spp., which grows on apples and pears in storage, causing them to rot, produces patulin, a compound which is much more toxic than most fungicides which would prevent the mold in the first place. 8
What is to Fear in Our Food?
The chemicals I’ve mentioned here are just a tiny sample of the naturally occurring compounds in fruits and vegetables that could harm us. These compounds are found in amounts that would make Vani Hari “The FoodBabe” blush. And there isn’t a darn thing we can do about them if we don’t want to starve or fail to get our proper nutrition. Everyday, your body is exposed to a cornucopia of natural carcinogens and toxins. They are produced endogenously by the plants we feed on and they are present in amounts many times larger than any artificial chemical. Yet, we have survived on these plants for thousands of years. Sometimes, as well, we have taken plants which would poison us, and manipulated them to produce edible cultivated varieties. We have little to fear from these chemicals.
Yet, there is more potential acute danger from these naturally occurring chemicals than from added chemicals like pesticides. Peanut mold, which produces aflatoxin, is much, much more dangerous than any fungicide used to control the mold. Indeed, more people are in danger from allergic reactions to food, or from reactions due to inborn errors in metabolism, than they are from what we add to our food. As well, we know much more about the metabolic fate of added pesticides than we do about most of the naturally occurring chemicals. We know less about these chemicals, yet we eat them without batting an eyelid, while being exceedingly fearful of those chemicals that we do know more about. 9 10
Far from being fearful of our food, knowledge of the millions of chemicals present in our foods which theoretically have the potential to harm us, but do not, should provide comfort. There are millions of chemicals, already present in our food, which have the theoretical potential to harm us. And yet, here we are, alive and kicking.
Apple with nutrition facts label © ecco – Fotolia.com
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- Riviere, J. Edmond. Chemical Food Safety: A Scientist’s Perspective. Ames, IA: Iowa State, 2002.
- Sauer, Jonathan D. Historical Geography of Crop Plants: A Select Roster. Boca Raton: CRC, 1993.
- Preedy, Victor R., Ronald R. Watson, and Vinood B. Patel. Nuts & Seeds in Health and Disease Prevention. London: Academic, 2011.
- Cliver, Dean O. Foodborne Diseases. San Diego: Academic, 1990.
- Lawley, Richard, Laurie Curtis, and Judy Davis. The Food Safety Hazard Guidebook. Cambridge, UK: RSC Pub., 2008.
- 6Riviere, J. Edmond. Chemical Food Safety: A Scientist’s Perspective. Ames, IA: Iowa State, 2002.
- Carlile, W. R. Control of Crop Diseases. London: Edward Arnold, 1988.
- Riviere, J. Edmond. Chemical Food Safety: A Scientist’s Perspective. Ames, IA: Iowa State, 2002.Riviere, J. Edmond. Chemical Food Safety: A Scientist’s Perspective. Ames, IA: Iowa State, 2002.
- Carlile, W. R. Control of Crop Diseases. London: Edward Arnold, 1988.