The Dark Side of Plant Foods

Most of us can remember being kids, and struggling to resist our parent’s advice as they would repeat, “Eat your vegetables, everyone knows they’re good for you”. What if our parents were wrong, though? Could it be that our natural aversion to eating vegetables as kids comes from an innate and factual basis? To answer this question, first we need to understand a few basics. To begin with, plants don’t want to be eaten anymore than animals do. Whereas animals defend themselves by running away, or by fighting with teeth and claws, plants resort to a variety of evolved defenses of their own. Some protect themselves with thorns, but most plants protect themselves by producing various toxins. These toxins are designed to keep animals from eating host plants. While certain animals have figured out ways to avoid some of these toxins, others have evolved physiological adaptations (like having four stomachs). Check out this interesting video about giraffes unique relationship with their primary food source, the acacia tree.

As mentioned, plants produce a wide range of toxins as a defense mechanism. Let’s look at the major groups of plant toxins, which vegetables contain them, and the possible adverse effects they can have on our health.

Isothiocyanates

Isothiocyanates are chemical compounds found primarily in the Brassica family of plants. These plants include broccoli, kale, cabbage, brussels sprouts, cauliflower, collard greens, and turnips. Brassica have been touted as cancer fighting foods, and these compounds have been shown to attack cancer cells. However, they are also indiscriminate, which means healthy cells are also attacked. Moreover, Isothiocyanates block the uptake of iodine by the thyroid gland, and are classified as goitrogens because they cause goiters. A study of Melanesian women with low iodine intake had a much higher incidence of thyroid cancer when they consumed cruciferous vegetables. These compounds have been repeatedly shown to have adverse effects on human cell cultures, and studies have shown that broccoli extracts fed to rats and mice cause DNA damage. Mice fed with isothiocyanate sulphoraphane showed hypothermia, loss of motor coordination, low white blood counts, and even death.

Polyphenols

Polyphenol containing foods are often hailed as “superfoods” and “antioxidants”. These are a group of compounds including resveratrol (grapes, red wine), curcumin ( tumeric), catechins (green tea), and genistein, (soy). Curcumin (tumeric) is marketed as an anti-inflammatory compound. However, there is accumulating data showing that it induces DNA damage to mitochondria and chromosomes inside the cell. Curcumin and other polyphenols have been shown to inhibit detoxification pathways in the liver. A group of polyphenols known as flavones (quercetin, tea, cocoa, soy) are phytoestrogens, meaning they mimic the effects of estrogen in our bodies. These act as endocrine disruptors. Animals fed high flavonoid diets have shown infertility, reproductive abnormalities, and reproductive tumors. Flavonoids can also act as digestive inhibitors, impairing Vitamin C and protein absorption. Resveratrol supposedly has anti-aging properties, but has repeatedly failed to show any benefit in human studies.

Oxalates

This encompasses oxalic acid and it’s salts which create sharp, needle shaped crystals. These can cause kidney stones and gout. High oxalate foods include tumeric, spinach, rhubarb, potatoes, sorrel, almonds, peanuts, rice bran, miso, beets, mushrooms and cocoa powder. Reports of serious complications and even death related to over consumption of oxalates have appeared in the medical literature for over 100 years. There is also evidence that excess oxalate consumption may trigger autoimmune disease. These needle shaped crystals can accumulate in many tissues. Women with vaginal pain (vulvodynia) often get significant relief when oxalates are removed from their diet. A 2011 study found that children with autism had three times the level of oxalates in their blood compared to non-autistic.

Lectins

Lectins have been in the spotlight lately thanks to Dr. Stephen Gundry and his book, “The Plant Paradox”. Lectins tend to be highest in the roots and seeds of plants, especially legumes (beans, cashews, peanuts), grains, seeds, nuts and tubers. Between 1976 and 1989, there were fifty incidents of poisoning related to eating incompletely cooked kidney beans in the UK. Lectins can cause serious gastrointestinal symptoms including diarrhea, gas, bloating and malabsorption of nutrients. They have been shown to negatively impact the gut microbiome by decreasing the diversity of our gut bacteria. These compounds can bind directly to the lining of the gut, causing increased gut permeability known as leaky gut.

The integrity of the gut epithelium is a critical barrier, and when it is breached can compromise our immune system resulting in food allergies and sensitivity, and has been implicated in triggering autoimmune diseases. Gluten is one of the most studied lectins, and has been implicated in inflammatory reactions, autoimmune disease, and even neurological disorders such as Parkinson’s. Plant lectins also mimic the actions of insulin, signaling fat cells to grow, potentially leading to weight gain.

Phytates

Phytates are derived from phytic acid which is found in grains, legumes, tubers, nuts and seeds. Phytic acid binds to minerals such as magnesium, zinc, iron, and calcium, and can inhibit or even completely block their absorption from the gut. A recent review published by the Mayo Clinic, regarding plant based diets, shares:

“We found that some of these nutrients, which can have implications in neurologic disorders, anemia, bone strength, and other health concerns, can be deficient in poorly planned vegan diets….Vegans may be at increased risk for deficiencies in Vitamin B12, iron, calcium, Vitamin D, Omega 3 fatty acids, and protein.”

So does this mean we should stop eating plant foods? Not necessarily. We need to remember that the effects of any toxin is dose dependent. For instance, a glass of wine once in a while is unlikely to harm us, but drinking a whole bottle will generally not be a good experience. I think it might be useful to look at this issue from an ancestral perspective. The Hadza are one of the few remaining hunter-gatherer tribes left. They have been extensively observed and studied in their home territory in Tanzania. They use plants mainly as medicine, and as fall back foods when they are unsuccessful in their hunts for animals. All observers have noted that they are strong and healthy, even into old age, and do not suffer from disease in spite of smoking a lot of tobacco and marijuana.

Try This Out

What does this mean for us? I believe we would benefit from limiting our consumption of the most toxic plants. Eating more low toxicity plants and fruits, and limiting high toxicity plants will give us the upside of consuming plants without the potential downside of adverse effects from plant toxins. Use the Plant Toxicity Scale below as a guide. Try eliminating the foods in high toxicity column for 4-6 weeks and notice how you feel. Pay attention to whether your symptoms improve. I will say from personal experience that significantly reducing my intake of nightshades and brassicas has made a huge difference for me, especially in my digestive system.