Phytochemicals are chemical compounds found in plants. Many can be beneficial in certain concentrations, such as flavonoids, carotenoids and antioxidants, yet can cause medical complications in excess. Phytotoxins (plant toxins) come in a wide variety of forms, but some of the most common are listed below. Many are targeted towards insect pests but can also affect reptiles, birds and mammals.
Oxalates, Glycosides and Goitrogens are the most common phytotoxins.
Oxalic Acid and Oxalates
Oxalic acid and oxalates both occur naturally in many plants, most of which can be eaten safely without complications. Oxalic acid is a the precursor to calcium oxalates, a potentially poisonous substance that contributes to the toxicity of antifreeze. Calcium oxalate is also the main contributor to the formation of kidney stones.
Oxalates and oxalic acid bind with calcium, leading to MBD (metabolic bone disease). They also form tiny crystals deposited throughout the body, causing pain, stiffness and impaired organ function. Lamb’s quarters, star fruit, black pepper, parsley, spinach, rhubarb, beets, chard, berries and beans are high in oxalate and/or oxalic acid. As many greens, fruits and vegetables have these phytochemicals present, they cannot be avoided. However, choosing staple foods with low amounts of oxalates will balance out the items with higher content. Animals with a healthy gut flora break down oxalic acid more readily.
Glycosides & Alkaloids
A Glycoside is a molecule in which a sugar is bonded to another molecular group. The chemical compounds are not always toxic in nature, but certain glycosides can cause complications in animals that ingest them. The bonds can be broken by digestive enzymes (or protective plant enzymes), leaving the non-sugar group (aglycone) in the bloodstream. Symptoms of glycoside toxicity include diarrhea, vomiting, and heart failure.
Glycoalkaloids are bitter tasting toxic compounds that cause a burning sensation in the mouth. Alkaloids can interfere with the nervous system and enzyme catalytic activities. For example, solanine glycoalkaloid is found in potatoes and other members of the nightshade family Solanaceae. Solanine poisoning results in gastrointestinal and neurological symptoms such as diarrhea, vomiting, and heart problems. Do not feed raw or green potatoes, and all other parts of the plants (leaves, stem, flowers, etc.) should be avoided.
Cyanogenic glycosides are present in many plants, which release toxic hydrogen cyanide when consumed. Rose family plants (cherries, apples, peaches, almonds, etc.) contain amygdalin cyanogenic glycoside in certain parts of the plants (especially the pits). Sorghum, uncooked cassava and the roots of lima beans, flax and clover also contain cyanogenic glycosides.
Saponin glycosides are compounds that cause hemolysis of red blood cells (hemoglobin degradation). Legumes, especially soy products, are relatively high in saponins and should be fed with caution. Cold-blooded organisms and insects appear especially vulnerable. (http://biocyc.org/META/NEW-IMAGE?type=PATHWAY&object=PWY-5203&detail-level=3)
Goitrogens are chemicals (in this case phytochemicals from plants) that suppress the function of the thyroid by interfering with iodine uptake. High levels of goitrogens in plant foods can cause induced hypothyroidism – increasing thyroid size and excretion of iodine. Thyroid hormones are associated with skin cells, growth and metabolism, so hypothyroidism can lead to trouble shedding, lethargy and slow growth.
Presence of high amounts of commercially prepared potassium iodine can prevent some adverse effects of goitrogens, especially in turtles.
The following foods (mostly cruciferous vegetables) are goitrogenic:
- Bok Choy
- Brussels Sprout
- Collard Greens
- Mustard Greens
- Nappa Cabbage
- Red Cabbage
- Turnip Greens
- Green Pea
- Grape Leaf
- Sweet Potato