Gottfried Fraenkel in the 1950’s proposed the hypothesis in his paper “The Raison d’être of Secondary Plant Substances” that plant secondary compounds/metabolites were not the waste products of plant metabolism but a means of ensuring plant protection from insects and other animals, as well as a communication system with pollinators.
There are two parts of a plant; Primary and Secondary compounds or metabolites. Primary compounds consist of carbohydrates, lipids, amino acids, nucleic acid and proteins. They are essential for the healthy growth, development and reproduction of plants – their architecture (for the most part) is the same across plant species. Examples of indispensable primary metabolites are the polymer cellulose – which gives plants their structure and chlorophyll which allows plants to absorb the sun’s energy.
There are approximately 45,000 distinctive plant secondary compounds, many of which have unknown biosynthetic pathways and plant protective functions. However, each is manufactured within the plant for particular reasons – specifically unique to each and every plant. Some are created by modifications done to primary metabolite pathways.
The bioactive secondary metabolites are not found uniformly throughout a plant, instead, they can exist mainly in the roots of the plant or be in the highest abundance in the flower. This is often determined by their polarity (hydrophobic and hydrophilic behaviour of the plant). However, their concentration and location in the plant will change from season to season (For example, in the summer secondary compounds may be found more potent in the leaves and flowers, whereas in the winter they may be more prevalent in the roots). Secondary metabolites are responsible for plant defences/protection against insects and other animals – the encompassing ecological environment – as well as communication with other organisms, such as that involving attracting pollinators.
Secondary plant compounds are extracted and utilized in the manufacturing and production of medicines, flavouring, recreational drugs and essential oils. They are also the compounds that are nutritionally vital and essential for health.
A lot of secondary metabolites are antioxidants. Antioxidants aid in boosting the immune system, reducing inflammation and bringing more oxygen into the body – which in turn aids against the development and assists in both the prevention of growth and the fighting of cancerous cells. Even before Fraenkel proposed his hypothesis, scientists have looked into the effects secondary compounds (though in 1806 it was unknowingly) were having on the body and seeing if they could be extracted. In 1806 morphine – a plant secondary compound – was extracted by a German pharmacist from opium poppies. Vanillin the secondary compound in vanilla bean was extracted by pharmacist Theodore Nicolas Gobley, after which in the year 1874 the chemical structure of Vanillin was discovered leading to the first artificial production of Vanillin/ Vanilla flavouring in 1876.
Although it is beneficial in some cases to have more potent doses of secondary compounds, it is also nutritionally beneficial to obtain them directly from the plants (and animals – as when animals eat specific plants the secondary compounds benefit their bodies, thus benefiting the consumer as well) as there is no doubt the secondary compounds are artificial (go for Non GMO, and local and organic whenever possible), moreover with hundreds sometimes thousands of secondary compounds present in a single plant there is potential that the positive effect on the body they provide is a joint effort (not enough is known or studied in terms of secondary compound interactions within a plant).
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Fraenkel, G. S. “The Raison D’etre Of Secondary Plant Substances: These Odd Chemicals Arose As A Means Of Protecting Plants From Insects And Now Guide Insects To Food”. Science 129.3361 (1959): 1466-1470. Online Available at PubMed.
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Amanda Filipowicz is a certified nutritional practitioner (CNP) with a bachelor in environmental studies (BES) from York University. She also has certification in clinical detoxification, prenatal and postnatal care as well as nutrition for mental health. She has been working as a nutritionist since 2013 and is a lifelong proponent of eating healthy.