12.1.5: The Good and Bad of Natural Plant Substances

One can see that it’s hard to separate the “natural” from the “unnatural.” It should also be clear by now that, contrary to popular sentiment, “natural” isn’t necessarily better than “unnatural.”

Plants—like all living organisms—are made up of a huge variety of substances. So many, that it’s impossible to test them all. As new varieties of plant life appear, so do new substances. Conversely, as varieties of plant life become extinct, so do some unique substances—including undiscovered medicinal substances.

Plants have long been a source of medicines. Even today, pharmaceutical companies continually search for—and find—novel medications in plants. The bark of the willow tree was known in ancient civilizations as a source of a substance that relieves pain. Based on this substance (salicylic acid), a German chemist synthesized aspirin (acetylsalicylic acid) in 1853. The heart medicine digitalis comes from the leaves of the purple foxglove plant.

Many anticancer drugs also come from plants, such as taxol (for ovarian cancer) from the bark of the Pacific yew tree, and vinblastine (for breast cancer) and vincristine (for leukemia) from the tropical flower rosy periwinkle. As more plants become extinct, particularly those in tropical forests, the worry is that the plants becoming extinct today contain what may have been tomorrow’s “miracle drugs.”

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Many people are severely allergic to peanuts. The peanut proteins responsible for the allergic reaction are being identified, in hope that the genes for these proteins can be eliminated or replaced by genetic modification to create allergen-free peanuts.⁵

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Those who like to divide substances into “good” and “bad” would have a hard time with a plant’s constituents. The easiest ones to categorize might be vitamins—but then, again, too much of even these can be toxic. Nutmeg, ginger, cloves, and cinnamon contain a bit of safrole—a carcinogen (cancer-causing substance). Sounds bad. Should we leave out these spices in our recipe for pumpkin pie? What about the caffeine in our coffee? Not so good when it makes the hand of a surgeon tremble during a delicate operation. But good when it keeps a tired surgeon awake on the drive home.

Do we include as plant substances those that form when a plant deteriorates or is cooked? Recall from Chapter 15, that animals that eat spoiled sweet clover can die of hemorrhagic disease, yet the same substance that causes their hemorrhage is used in much smaller doses as human medicine to prevent clots that can lead to a fatal heart attack. Almonds and lima beans are among those foods that produce hydrogen cyanide when cooked or digested—the same poison used in the gas chamber for capital punishment.

But some plant substances are outrightly classified as toxins.⁶ Plants contain a variety of these, often in very large amounts. This isn’t surprising. To survive, plants must have their own defenses against predators—thorns are the closest they come to having claws to defend themselves, and they can’t run from their enemies.

Among these toxins are the naturally-occurring pesticides alluded to earlier. In fact, the amount of synthetic pesticide residues in our food pales in comparison to the amount and variety of naturally-occurring pesticides in our food.^7,8

Some of these naturally-occurring pesticides have chemical actions identical to those of the pesticides farmers apply to their crops. For example, some plants contain substances that play havoc with the transmission of nerve impulses. From the plant perspective, this is an ideal toxin—plants don’t have nerves, whereas most of their predators do.

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Nerve impulse inhibitors are also used in flea collars—a big dose for fleas, a small dose for cats or dogs. During the 1991 Persian Gulf War, we feared that Iraq would use them in nerve gases—in big enough doses to kill humans. The substances can stop breathing through a spasm of the respiratory muscles.

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Since we have nerves, these substances can be toxic to us as well. But a large dose for an insect is a very small dose for us. Again we’re reminded that what’s toxic or not is in the size of the dose.

What’s Good and What’s Bad?

There are valid arguments to be made concerning what and how much of various substances should be allowed in our food. But we confuse rather than enlighten if we focus only on those that we add to food. We do better when we compare these objectively to those that are there “naturally” as part of a native species, or are incorporated by conventional crossbreeding techniques, or are there because of infection by plant microorganisms, the presence of insects, or “natural” deterioration.

Figure 20-4: Cancer-causing potential of natural vs. residue from synthetic pesticides in our food^5,6

Especially now, when we have more options than in the past, and we see agriculture in the context of world ecology, there’s a much greater need for more objective public dialogue: Is it reasonable to spend more on “organic” produce because of concern about pesticides? What if the particular organic produce happens to “naturally” contain more pesticides? How much are we as taxpayers willing to support Integrated Pest Management Programs as a way to minimize pesticide use?

There are valid concerns about pesticide sprays. The spray isn’t confined to the pests alone and can upset the natural ecology. There’s the danger of accidental spills, and worry of the hazards to farm workers. Again there’s the potential trade-off with the possible use of biotechnology to make the crop plant more disease resistant so that less or no spraying is needed.

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In 1970, about 15% of the U.S. corn crop (over a billion bushels) was lost to corn blight. Most of the corn in the U.S. were the same “super variety” of hybrid corn, developed by crossbreeding.

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Some who argue against genetically modified crops correctly state that the development and widespread use of “super varieties” reduces genetic diversity, making much larger portions of crops vulnerable to a single disease, extreme weather condition, etc. Crops with the same genes have the same genetic susceptibilities.

This isn’t a new concern. It has been, and still is a concern in the development of “super varieties” by conventional crossbreeding as well.⁹ In large part because of this concern, the National Seed Storage Laboratory in Colorado maintains a stock of wild and “older” varieties of plants.

Non-scientists are understandably uneasy with regard to science and technology. Dramatic changes can seem “unnatural” at first, even those we later take for granted—the Wright brothers flying through the air, inoculation with a vaccine, the splitting of an atom.

The uneasiness is greater today, because of the wide gap between the general public’s scientific literacy. and the increased complexity of scientific achievement. When the Wright brothers took off, this gap was narrow, and everyone could make a reasonable assessment of the bright and dark sides of aircraft. Today the situation is far different, particularly in areas like biotechnology—even though we all still do share a common goal of doing what’s best for our own body, our own community, our own world.