The Truth About Natural Toxins in Fruits & Vegetables

A ROGUE’S GALLERY OF TOXINS

It’s true that plants produce a staggering number of enzymes, and many of these enzymes are used to make complex chemical compounds involved in defense against pathogens and animals. They’re known collectively as “specializing compounds.”

Without them, it seems, there’d be much greater crop loss to herbivores, which would have devastating consequences for farmers as well as society.

These potentially toxic substances are found in the roots, tuber, stem, fruits, bud, and foliage of plants. It’s true that when consumed in sufficient amounts, these toxins can indeed cause considerable harm – or at least discomfort – to humans. These toxins can enter the body by inhalation, swallowing, or actual contact.

These toxins fall into one or more of the following classifications:

TOXIN: ALKALOIDS

• Foods that contain them: Potatoes, eggplant, coffee beans, tea leaves.
• How they can damage you: Alkaloids are organic compounds derived from an amino acid, most of which exhibit strong physiological effects. Most affect the central nervous system, but some can also cause veno-occlusive disease of the liver (where the small blood vessels get blocked).

TOXIN: GLYCOSIDES

• Foods that contain them: Lima beans, the shell of soybeans, flaxseeds, bamboo shoots, apricot, and peach pits.
• How they can damage you: Glycosides come in a couple of unpleasant varieties. One type – cyanogenic glycosides – attaches to mitochondrial cytochrome and blocks electron transport, which leads to coma. Another variety, cardiac glycosides, inhibit an enzyme that controls heart rhythm.

TOXIN: PROTEIN TOXINS

• Foods that contain them: Castor plant (ricin), abrin, white acacia.
• How they can damage you: Protein toxins can get inside the cells and prevent them from making the proteins they need. See various episodes of “Breaking Bad” where Walter White poisoned people with ricin.

TOXIN: OXALIC ACID/OXALATES

• Foods that contain them: Spinach, legumes, soy products, potatoes, etc.
• How they can damage you: Oxalates contain needle-sharp crystals that can irritate the skin, mouth, tongue, and throat, which can result in difficulty in breathing, burning pain, and stomach upset. Oxalate can also bind to calcium, resulting in severe hypocalcium with tetany (muscle spasms).

TOXIN: ANTI-VITAMINS

• Foods that contain them: Horsetails, bracken (a type of fern), cinnamon, Mexican vanilla, tonka beans, strawberries, apricots.
• How they can damage you: Anti-vitamins are toxins that work against vitamins. Coumarin, for example, found in relatively large amounts in cinnamon, breaks down vitamin K, whereas horsetail and bracken break down thiamine.

TOXIN: FUROCOUMARINS

• Foods that contain them: Parsnips, celery roots, citrus plants.
• How they can damage you: Furocoumarins can cause gastrointestinal problems in certain individuals. They’re also phototoxic, which means they can cause severe reactions when skin is exposed to sunlight.

TOXIN: LECTINS

• Foods that contain them: Legumes, kidney beans, peanuts, grains.
• How they can damage you: Lectins can cause stomachache, vomiting, and diarrhea.

HOW COME WE’RE NOT ALL SICK OR DEAD?

In most cases, the aforementioned plant toxins affect the nerves (neurotoxins) or important cellular functions (cytotoxins). However, most of us have eaten many, if not all, the foods listed without experiencing the slightest physiological reaction. What gives? How come we ain’t all dead?

Well, as is the case with most things that are “bad for you,” dosage plays a big part in toxicity.

Eating one-fourth of a cup of kidney beans as a side dish, for example, is different than eating a kettle full. Eating too many Brazil nuts can poison the lungs and the liver by introducing an excess of selenium, but eating just a few supplies an essential nutrient that leads to the production of an enzyme instrumental in protecting against heart disease and cancer.

But aside from eating sane doses of various potentially toxic fruits or vegetables, there are plenty of ways we inadvertently neutralize many of these toxins. Ever eat part of a plant and find it to be bitter? The bitterness acts as a warning that maybe we should exhibit caution when ingesting said plant, but often, just cooking the plant makes the bitterness go away, i.e., neutralizes the toxins.

But could these assorted plant toxins, in smallish doses, actually be good for us? Could they be part of what makes fruits and vegetables healthy? There’s a theory that posits just that. It’s called hormesis.

HORMESIS: HAVE SOME MORE NEUROTOXIN, SO YOU GROW UP BIG & STRONG

We all know fruits and vegetables contain antioxidants. It’s these antioxidants that get all the credit for improving health, but the story’s not that simple. In many cases, studies involving individual antioxidants (like vitamins C, E, and A) have failed to ameliorate or cure disease. They’ve even been shown, in sufficient doses, to kill or disrupt neurons.

But conversely, there are plenty of studies where these toxins have been shown to protect the brain against diseases like Alzheimer’s and various other neurodegenerative diseases.

Clearly, there appears to be something else going on and that something else might be hormesis. You know how exercise makes a body healthier, as does going without food for a while (which causes, among other things, an increase in the production of life-extending compounds, like SIRT1). Exercise and fasting expose the cells to stress, and their response is to bolster the cell’s health so that it comes back stronger.

Plant toxins, according to the theory of hormesis, act the same way. The mild stress they impose on various cells causes them to “retaliate” with any number of chemical reactions that make the cell more resilient to further stress, whether it comes from plant toxins, pathogens, or disease.

This isn’t just some bullshit homeopathic theory, either. There are scientists who’ve been studying the phenomenon for decades, and they’re cocksure that the health effects of these dietetic stressors either complement or surpass those of antioxidants.

Edward J. Calabrese, a professor of toxicology at the University of Massachusetts, has spent the last 30 years analyzing more than 10,000 published studies in the fields of toxicology, medicine, and biology. He’s used the results to establish a scientific society dedicated to research on hormesis.

Take, for example, the polyphenol curcumin. Most of us are aware of its myriad health benefits. Among those benefits is the possibility that it might ameliorate Alzheimer’s, for example. And sure enough, experiments with mice found that curcumin reduced the buildup of beta-amyloid (a protein that literally gunks up the brain) and lessened the severity of the disease.

The results were initially thought to be because of curcumin’s ability to mop up free radicals, but later experiments found that the polyphenol causes mild stress to brain cells. In turn, this mild stress triggers the production of antioxidant enzymes that stifle the production of free radicals and the accumulation of toxic proteins, beta-amyloid among them.

OTHER EXAMPLES OF HOW “TOXIC” SUBSTANCES ARE HEALTHFUL

Caffeine, capsaicin (what makes peppers hot), and catechins from tea are all hormetic substances. While toxic in larger amounts, sane, everyday doses act on channels in the cell membrane to allow calcium ions to enter and initiate the production of DNA and RNA.

Garlic and hot peppers do the same thing for the brain: they open channels in the outer membrane of nerve cells so that calcium ions can enter. Higher than normal levels of electrical activity occur, a type of stress that seems to protect cells from the hyperactivity that occurs during a stroke.

Resveratrol, another famous polyphenol, activates SIRT1, which then switches on several chemical pathways that regulate hormetic effects.

Scientists who study hormesis measure the effects of plant chemicals by using a “biphasic response curve.” They make a graph that plots effects relative to dose and then make a line with an upside-down U shape. This “effect line” rises at first to show that eating a small amount of a plant or chemical has beneficial effects, but then it gradually plummets down to show the plant’s toxicity as more of the substances are eaten.

DOES THE BODY NEED TO “REST” FROM EATING FRUITS AND VEGGIES?

You know how earlier I used the example of exercise to demonstrate how introducing a stressor (in this case, the exercise itself) can lead to beneficial effects? Well, as you know, in order for exercise to be consistently beneficial, it needs to be interspersed with rest and repair.

Well, it appears that hormesis – the beneficial stress response to certain plant chemicals – also requires rest and repair periods. Apparently, you can’t keep stressing the system continually without rest periods and expect things to keep getting better and better.

When you eat fruits and vegetables, the body enters a “stress resistance mode” where the body concentrates on the removal of damaged molecules and the manufacture of a certain protein needed for cell survival.

However, it’s detrimental for the body to stay perpetually in this mode. The body needs to make proteins for other purposes; if unabated, the dietary stressors can overstress the body until it starts to deteriorate.

Luckily, this doesn’t mean you have to start taking days off from eating plant foods, as you would with exercise. The evidence suggests that just a normal night of sleep is enough time to allow the cells to recover from any excess hermetic stress imposed by the plants you consumed that day.

WAYS TO NEUTRALIZE TOXINS

Maybe you buy the hormesis thing and you can now eat your fruits and vegetables without feeling like you’re Socrates drinking his hemlock tea. Maybe you don’t buy it and still believe that the toxins in plants can negatively affect your health. Fine. Let’s tackle your problem a different way and explore ways you can prepare certain allegedly problematic foods so that you lessen or negate the toxins.

POTATOES

Potatoes contain glycoalkaloids, low levels of which give potatoes their flavor. However, elevated levels of glycoalkaloids have a bitter taste, warning you that a particular potato should be chucked into the trash. Unfortunately, glycoalkaloids are impervious to cooking, even in hot oil.

Luckily, most of the glycoproteins can be found in the peel or just below the peel, which is often indicated by a green color (red-skinned potatoes or russet potatoes can camouflage the green).

In general, avoid potatoes that show signs of physical damage, greening, or sprouting. Or you can just peel or cut away green areas prior to cooking.

KIDNEY BEANS

Kidney beans contain lectins, but they can be largely neutralized by soaking them for around 5 hours and then boiling them for at least 10 minutes. Cooking them in a slow cooker is not recommended by the people who ascribe to these toxicity issues. Canned kidney beans, however, are thought to be safe to eat without further cooking.

PARSNIPS

To neutralize the furocoumarins found in parsnips, peel them before cooking and remove any parts that look suspect. Further, baking, microwaving, or boiling seems to do a good job of destroying the toxins.

ZUCCHINI

No special instructions here other than common sense: if it smells bad or tastes bitter, ditch it.

While there are known ways to neutralize the toxins in a few other plants, most are foods that aren’t generally a part of the Western diet (rhubarb, kumara, cassava, bamboo shoots, etc.), so I’ll refrain from explaining how to make them safe(er).

SO WHAT SHOULD YOU DO?

I now understand the fear of eating fruits and vegetables and why many people on the carnivore diet avoid them. That doesn’t mean I agree with them.

At the very least, eating only muscle meat is likely not a good strategy. As I often point out, native American Indians, upon making a kill, would discard the muscle meat because they had learned, through generations of experience, that muscle meat is relatively poor in nutrients. They would literally feed it to the dogs and instead eat the comparatively nutrient-rich organ meat.

No, fruits and vegetables present far too many health benefits – most probably still unrealized – for anyone interested in health to curtail the amount they eat, let alone avoid them entirely.

And the hormesis thing? Maybe it’ll prove to be wrong. Regardless, avoiding entire groups or classifications of foods is unlikely to prove healthful in the long run.

It’s as if, upon learning about the dangers of sun exposure, people burrowed deep under the ground and lived like mole people. It’s as if, upon learning of the danger of overconsumption of water, people went full Dune and lived like the Fremen on Arrakis with their stillsuits that only lose a thimbleful of water a day.

Dosage, as it is with most things, is paramount. Eat traditional serving sizes of various fruits and vegetables instead of bucketfuls (as if you needed to know that).

Additionally, don’t try to subsist on a single fruit or vegetable that appeals to your palate. Don’t eat the same ones every day. Instead, eat a variety. Don’t eat it if it looks or smells funky.

Hell, if your lovemaking involves rubbing mango fruit – a known skin irritant – on your partner, choose another fruit with which to pulp them up.

In general, and at the risk of being over-simplistic, use common sense.

REFERENCES

1. Friday OA. Plant Toxins. Am J Biomed Sci & Res. 2019 – 4(3).
2. Mattson MP. What Doesn’t Kill You. Sci Am. 2015 Jul;313(1):40–45. PMC.
3. Natural toxins in vegetables and beans. New Zealand Food Safety.
4. Natural toxins in fresh fruits and vegetables. Canadian Food Inspection Safety.
5. Naturally occurring toxins in vegetables. Centre for Food Safety. Hong Kong. 2005 Dec.
6. How Plants Make, Store and Use Toxins. Genetic Science Learning Center.