A recurring question when studying herbal medicine is how and why plants have a beneficial affect on people’s health. The answer to this question varies by the cultural filter through which the plant world is viewed. One view that has helped my understanding of herbal medicine is the subject of Plant Metabolites.
Nature does not waste energy. If a plant uses its resources to produce bark, leaves, fruit, flowers or thorns, there are good reasons for these. If a plant produces starch, fats, alkaloids or tannins, there are good reasons for those also. The end result of what a plant creates is called a metabolite.
Primary Metabolites as Food
There are two types of metabolites: primary and secondary. A primary metabolite has an immediate and vital role to play in sustaining the life of the plant. These include fats, protein, starches, chlorophyll and carbohydrates.
Chlorophyll is a pigment used in photosynthesis. The dark green color of kale is an example. The starch filled tuber of a potato plant or the rhizome of a cattail provide food for these plants to grow. The sap of the maple tree provides energy for new growth each spring. The oil contained in olives and avocados are also in the primary metabolite category. In general, this type of metabolite provides food for humans.
Secondary Metabolites as Medicine
Secondary metabolites are the topic of much current research and our view of these is evolving. Their basic role is to support the vital functions of the primary category. They are what plants make to solve problems of life support: predation, environmental stress, growth and reproduction. They do this by attracting pollinators by either smelling or looking good, repelling herbivores by either tasting bad or being toxic or repelling pathogens by being active against bacteria and fungus.
Types of Secondary Metabolites
A common and well known category of secondary metabolites is volatile oils. When processed and bottled, these are called essential oils. In general, volatile oils either attract or repel. Flower oils attract pollinators while oils in other parts of the plant work as a type of immune system for the plant by either repelling through aroma or actual killing of various microbes. Citronella essential oil is well known as a mosquito repellent and eucalyptus essential oil is often used to repel fleas. Some of the most used and researched anti-microbial essential oils are Oregano, Thyme, Tea Tree, Tulsi, Monarda, Clove and Eucalyptus.
Typically ending in -ine (caffeine, nicotine, berberine), this category frequently makes the plant either toxic or taste bad. Both the deadly poison & water hemlocks and most other plants toxic to humans contain alkaloids.
Their primary roles in herbal medicine is to either stimulate or sedate the nervous system or support the immune system. Caffeine is a widely used stimulant while morphine is a sedative pain killer. Perhaps the best known immune supporting alkaloid is berberine, found in Barberry, Oregon Grape, Goldenseal and Coptis. It is frequently used for its ability to assist the body in controlling fungus and bacteria.
On occasion, alkaloids can be hallucinogenic and part of spiritual ceremonies for humans. The alkaloid-containing Ayahuasca from South America has a long and well documented use as an entheogen.
This constituent is responsible for the drying astringent effect on human tissue, whether topical or internal. In direct physical contact, tannins cause the mouth to pucker and dry almost instantly. Any leaf or plant part high in tannins is un-palatable so it is an effective deterrent to herbivores. The human use of tannins is often connected to reducing the flow of fluids such as diarrhea or contracting inflammed tissue such as a swollen mosquito bite or poison ivy.
This is a brief overview and introduction to secondary metabolites. It is a relatively recent field of study and new ones are still being discovered and researched. Remember: we use plant metabolites in ways very similar to their use in the plant world. Primary metabolites are used as food, secondary metabolites are used for medicine.