Have you ever taken black coffee/tea with no sugar, or concoctions your mother made you from some roots and barks of plants, claiming that it would cure your stomach ache? If yes, then we can agree that these infusions are far from sweet. The taste of these infusions is attributed to the naturally occurring compounds called phytochemicals or secondary metabolites that are present in plants.

Phytochemicals are non-nutrient plant compounds produced through secondary metabolism and play a role in plant growth and defense against competitors, pathogens, or predators. These phytochemicals are significant to plants as much as it is to humans. The major classes of phytochemicals include polyphenols, terpenoids, and steroids, alkaloids, tannins, saponins, and thiols. These classes are representative of the large array of different phytochemicals that have been identified and characterized. Researchers suggest that there are many more phytochemicals present in nature that are yet to be identified, isolated, and characterized.

Secondary metabolites help to protect plants from harmful agents such as insects and microbes, as well as stressful events such as ultraviolet irradiation and extreme temperatures. Phytochemicals attract beneficial birds and insects through scent, therefore promoting pollination, germination, and seed dispersal. Other secondary metabolites are very toxic to animals therefore deterring or even killing plant enemies. Phytochemicals give plants color and an array of flavors both pleasant and unpleasant when consumed. These natural compounds provide clinical health benefits when consumed.

Since time immemorial, herbalists would prescribe plant concoctions and infusions to treat various human illnesses. They would ask the patients to chew the plant part or rub it on their skin in the case of skin diseases. They would also grind, soak or boil various parts of plants in water to extract these phytochemicals into solution, making them readily available for absorption into the body system.

Interestingly, the herbalists did this all without the knowledge of which plant compounds are responsible for the curative effects observed and without the knowledge of how extraction works, in terms of isolating these diverse compounds from the plant parts. Research shows that plant secondary metabolites provide health benefits when consumed, and with advancing technology, scientists can determine the structure of the phytochemicals and test their biological activity and efficacy, in-vivo and in-vitro.

Role of Phytochemicals in human health

Phytochemicals have the potential to prevent diseases and act as anti-microbial, anti-inflammatory, anti-oxidant, pro-oxidant, anti-tumor, immunomodulatory, detoxifying, and neuropharmacological agents. This means that secondary metabolites have negative effects on aging, cancer, diabetes, osteoporosis, auto-immune diseases, neurodegenerative diseases and many other pathologies. Phytochemicals also have analgesic and central nervous system stimulating properties. Alkaloids such as caffeine, nicotine, morphine, and cocaine have the ability to cross the blood-brain barrier and exert depressant or stimulant effects.

The table below summarizes the biological activity of the different classes of phytochemicals.

ClassificationMain groups of compoundsBiological function
NSA (Non-starch poly-saccharides)Cellulose, hemicellulose, gums, mucilages, pectins, ligninsWater holding capacity, delay in nutrient absorption, binding toxins and bile acids
Antibacterial and antifungalTerpenoids, alkaloids, phenolicsInhibitors of micro-organisms, reduce the risk of fungal infection
AntioxidantsPolyphenolic compounds, flavonoids, carotenoids, tocopherols, ascorbic acidOxygen free radical quenching, inhibition of lipid peroxidation
AnticancerCarotenoids, polyphenols, curcumine, FlavonoidsInhibitors of tumor, inhibited development of lung cancer, anti-metastatic activity
Detoxifying AgentsReductive acids, tocopherols, phenols, indoles, aromatic isothiocyanates, coumarins, flavones, carotenoids, retinoids, cyanates, phytosterolsInhibition of procarcinogen activation, inducers or drug binding of carcinogens, inhibitors of tumorigenesis
OtherAlkaloids, terpenoids, volatile flavor compounds, biogenic aminesNeuropharmacological agents, anti-oxidants, cancer chemoprevention
Bioactive Phytochemicals in Medicinal Plants.

The antimicrobial plant compounds include flavonoids, tannins, saponins, and phenolic compounds. These phytochemicals act as antibacterial and antifungal agents through various pathways that interfere with microbial growth, structural integrity and metabolism. Anti-malarial drugs such as Artemisinin’s and Quinine are derived from plant compounds. Artemisinin belongs in the class of terpenoids while quinine is an alkaloid. These drugs have been very important in the control of malaria parasites despite the recent development of resistance by the Plasmodium parasite.

Some phytochemicals such as flavonoids, alkaloids, vitamin C, and anthocyanins have antioxidant effects, meaning that they can be able to prevent or slow damage to cells caused by free radicals. Free radicals are unstable molecules that the body produces as a reaction to stress and environmental pressure. The damage caused by free radicals leads to changes in cells, and these changes have been linked to cancer, cardiovascular diseases, neurodegenerative diseases, inflammation, and vision loss. An intake of antioxidants has been proven to reduce these risks. The anti-inflammatory and detoxification effects of phytochemicals are largely attributed to their antioxidant activity.

Some phytochemicals have also been proven to have neuropharmacological activities. They include phenols, alkaloids, flavonoids, saponins, and terpenes which play a vital role in maintaining the brain’s chemical balance by influencing the function of receptors. Herbal medicines have long been used to treat neural symptoms, although the precise mechanisms of action of herbal drugs have not yet been determined. However, some of them have been shown to exert anti-inflammatory and/or antioxidant effects in the nervous system. Flavonoids have been proven to reduce neuroinflammation and oxidative stress therefore reversing the symptoms associated with Alzheimer’s disease.

Medical scientists are now gearing towards ethnopharmacological studies, which focus on the use of traditional medicine in local communities, including its commercial applications. This will be helpful in identifying novel therapeutic compounds for treating various diseases especially with the advent of multidrug resistance characteristics among pathogens. There are large quantities of toxins in the air, food, soil, and water, so our body requires naturally occurring herbal substances, to help heal and detoxify. To get the most nutrients, always buy fruits and vegetables that are organic.

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