Plant defence mechanisms

In nature, animals can easily defend themselves by running away, fighting or camouflage. But how do plants stop themselves from being eaten by insects and animals? Plants have evolved over millions of years, they have developed sophisticated mechanisms to both protect themselves from animal and also to encourage animal contact:-

  • A cactus plant has spikes to stop animals eating the juicy flesh.
  • Rhubarb leaves contact the deadly poison oxalic acid.
  • Raw cruciferous vegetables block of the transport of iodide of animal cells (causing thyroid issues and goiter).
  • A coconut has a hard protective shell.
  • A rose plant has thorns to protect the stem, yet has beautiful flowers that attract bees.
  • Some plants produce sweet tasting fruits to ensure that they are eaten and their seeds spread.

A diet rich in fruits and vegetables is generally a good thing, but it is worth noting that some plants or excessively eating some plants can have serious health effects. This was recently made famous when Professor Jordan Peterson went on a meat only carnivore diet. He did this to try and eliminate certain foods that were giving him severe mental issues and depression. Read further to discover some of the common plants that can cause havoc.

The best advice is to eat a varied plant diet and to not excessively eat one type of fruit or vegetable. The cooking method also plays an important role.

Many plants produce secondary metabolites, known as allelochemicals, that influence the behaviour, growth, or survival of plant eating animals, including humans. These chemical defences can act as repellents or toxins to plant eaters, or reduce the plants digestibility.

Plants have evolved many secondary metabolites involved in plant defence, which are collectively known as antiherbivory compounds and can be classified into three groups:

  • Nitrogen compounds (including alkaloids, cyanogenic glycosides, glucosinolates and benzoxazinoids),
  • Terpenoids (used for their aromatic qualities and play a role in traditional herbal remedies).
  • Phenolics (these can have positive and negative health effects).

Several plants use a bitter taste for protection. These chemicals are called alkaloids and can inhibit or activate enzymes, or alter carbohydrate and fat storage. Certain alkaloids bind to nucleic acids and can inhibit synthesis of proteins and affect DNA repair mechanisms. Alkaloids can also affect cell membrane and cytoskeletal structure causing the cells to weaken, collapse, or leak.

Plants have evolved complex chemical protections against being eaten. Be aware.

Kale & cruciferous greens
All cruciferous vegetables like kale contain thiocyanates which are considered goitrogenic (they deplete iodine from the thyroid) because they contain. these include arugula, bok choy, broccoli, brussel sprouts, cabbage, cauliflower, collard greens, mustard greens, turnips and watercress. Cooking breaks down the thiocyanates. You can also supplement with iodine to mitigate the risk.

Spinach and oxalates
Exposures to plants containing oxalate crystals are among the most common toxic plant exposures. Oxalates can bind with dietary calcium  or magnesium to form insoluble oxalate salts, which then may lead to low serum calcium and magnesium levels as well as to renal failure because of precipitation of these salts in the kidneys. Oxalate rich plants are spinach, bran flakes, rhubarb, beets, potato chips, almonds, cashews, french fries, some nuts and nut butters. If you are worried about kidney stones you should limit oxalates. Boiling your vegetables will cause the oxalate to leach out of them. Boiling spinach reduced the amount of soluble oxalate by more than 60%. (Plants carry both soluble and insoluble oxalate. It's generally harder to reduce insoluble.

Phytates are phosphorous compounds found in whole grains, legumes, nuts and seeds. They can bind to dietary minerals including iron, zinc, manganese and calcium which slows their absorption. Some nut and seeds may seem really healthy due to their mineral content, but their phytate content makes the minerals less bioavailable. For instance sunflower seeds are high in zinc but also high in phytate. Corn is high in phytates, you could have a mineral rich meal and the corn would eliminate all the absorption.

Limes contain psoralens that react with ultraviolet light and that can produce skin issues and hyperpigmentation on areas of the skin that have come in contact with lime juice. This is known as phytophotodermatitis and is seen with other psoralen-containing plants, such as celery. Eating things that are high in psoralens can also cause issues.