Of the approximately 400,000 species of plants on Earth, only a tiny fraction are edible by humans. Among the edible plants, typically only a portion of the plant is safe to eat; the rest is often harmful to humans. Even today, plant poisonings are still relatively common events.
Most of the produce that we see in the supermarket has absolutely no resemblance whatsoever to the plants that would have been available to our ancestors 50,000 years ago. Cruciferous vegetables basically didn’t exist, and our ancestors would have avoided leafy greens because of their extremely bitter taste. Tubers and other starchy “underground storage organs” were not particularly tasty and would have been primarily composed of fibrous, tough material. Nuts and seeds are well-protected physically by a tough outer shell or more subtly by toxic chemical defenses. Unprocessed nuts or beans can be among the most deadly plant-based foods around. Plants are especially protective of their offspring. The fruits we eat today have been manipulated to the point that prehistoric people wouldn’t recognize them.
We know that plants are full of chemicals, many of which serve as pesticides. If we had to introduce those same natural plant pesticides to the market today and subject them to rigorous toxicity testing, many of those chemicals would not be allowed on the market. However, because there is no real regulatory organization that examines “natural substances” in food, we tend not to worry about it.
I’m not saying that researchers have never studied these naturally occurring plant compounds in everyday fruits and vegetables. In fact, there are numerous studies on this topic. In 1990, famed toxicology researcher Professor Bruce Ames investigated the use of pesticides in food production and compared manufactured pesticides to naturally occurring plant-chemical pesticides. Shockingly, Ames found that 99.9 percent of pesticides we consume by volume comes from plants themselves. When he examined some of these compounds in more detail, a majority were shown to cause cancer in animal models. We shouldn’t run away from all fruits and vegetables because of a potential cancer risk. However, it does show us that there are plenty of chemicals in the plant foods we eat, and many of them have a potentially negative effect.
Plants Waging Chemical Warfare
The list of chemicals found in the plants we commonly consume is extensive, and I’m not going to list them all. However, I’m covering some of the more common ones so I can talk about the potential and documented effects. Remember, researchers have studied many of these compounds in limited capacities, and we likely will never know all the potential interactions and issues that may be related to them. It’s also important to note that although a particular compound may cause a major problem in one person, another person may not experience any obvious issues.
Commonly found in leafy green vegetables, some fruits, nuts, seeds, and even French fries, oxalates are a pretty common antinutrient. They can lead to medical problems—particularly when people ingest them in higher doses. One of the most common issues is kidney stones, which often are comprised of oxalates. Oxalate crystals in the body can become very needlelike, and some research has associated them with gastrointestinal irritation. The crystals may lead to leaky gut syndrome and potentially can lead to autoimmune issues.
Lectins, recently made popular by Dr. Steven Gundry’s book, The Plant Paradox, are a fairly ubiquitous plant compound, but they’re particularly concentrated in things like grains, nuts, corn, quinoa, fruits, nightshades, vegetable oils, legumes, beans, and squash. The trouble with lectins is that they can lead to a leaky gut situation and likely contribute to all the potential downstream effects of leaky gut.
Glycoalkaloids are in nightshade plants like potatoes, tomatoes, eggplants, and peppers. Limited evidence suggests these compounds have a connection to leaky gut syndrome and autoimmune problems like psoriasis. The foods that contain glycoalkaloids—particularly the nightshade vegetables—have been reported to worsen symptoms of irritable bowel syndrome (IBS).
Goitrogens are substances that can interfere with the function of the thyroid. Thyroid dysfunction is particularly common among women, and some researchers believe that high amounts of goitrogen-containing foods may play a role. Foods like soy and cruciferous vegetables tend to be high in these substances. Perhaps all those years of forcing ourselves to choke down broccoli and cauliflower were not kind to our thyroids.
Cyanogenic glycosides are in common foods like almonds, flaxseed, linseed, lima beans, cassava, and certain stone fruits (such as cherries, peaches, and plums). Cyanide poisonings can and do occur, commonly with consumption of cassava root; sometimes death is the result of poisoning. Chronic exposure to cyanides is postulated to contribute to chronic diseases such as impaired thyroid function and neurological disturbances.
Phytic acid is in grains, seeds, nuts, and legumes. It can lead to mineral deficiencies, particularly deficiency of zinc, calcium, magnesium, and iron. Deficiencies in these minerals can lead to a host of potential problems, including heart disease, depression, infertility, impotence, hair loss, and compromised immune function. On the beneficial side, phytic acid has been shown to lower blood glucose and potentially lessen the formation of kidney stones.
Protease inhibitors are in most legumes, particularly soy; cereals; fruits such as kiwi, pineapple, papaya, bananas, figs, and apples; and vegetables such as cabbage, potatoes, tomatoes, and cucumbers. The protease inhibitors interfere with the activity of enzymes involved with protein digestion, such as trypsin, and in animal studies, they have been shown to lead to poor growth in subjects. Conversely, there is some evidence to show these compounds may have a positive role in limiting cancer.
Flavonoids, which are responsible for some of the pigment found in plants, are commonly found in citrus fruit, cocoa, blueberries, parsley, onions, and bananas. They’re potentially beneficial at low levels, but in higher doses, they’ve been noted to cause genetic mutations, oxidation that leads to free radical production, and inhibition of hormones.
Saponins are in legumes, beans, garlic, alfalfa sprouts, peas, yucca, and asparagus. They have been shown to cause digestive disturbances, thyroid problems, and damage to red blood cells. Fun stuff indeed!
Salicylates are in many fruits and vegetables and some spices. They’re often responsible for sensitivity reactions that can trigger asthma, gut inflammation, and diarrhea.
Humans survived an Ice Age, which means our ancestors’ habitat was like Iceland, not Costa Rica. If we’re willing to set aside our arrogance about how much we think we know and apply some commonsense observations, we can see how impractical a diet full of indigestible fiber and nonessential phytonutrients is. We need fat, protein, and some vitamins and minerals. We require no other nutrients to live or—I’ll argue—to thrive. We require zero carbohydrates, zero phytochemicals, and zero fiber.
Excerpted from The Carnivore Diet, By Dr. Shawn Baker.
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