The Sweeter Side of Bitter Gourd

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Introduction

Natural products are one of the most precious gifts of nature. Their healing properties have been known to man since pre-historic times. Some of the natural products that were used include plants, animals, microbes and marine organisms. The data collected from the fossils indicate that the application of the natural plants as medicines dated back to 60000 years. It is presumed that the challenges faced by the ancient man while looking for food proved to be a learning experience to distinguish between poisonous and edible plants. This preliminary knowledge gained by pre-historic man provided a strong base for the evolution of traditional system of medicine.

The traditional medicine is regarded as an art that incorporates traditional treatment techniques as well as knowledge and beliefs related to the application of medicines sourced from nature. Also included in the traditional methods are the spiritual healing practices, manual methods which includes certain hands-on techniques for relieving muscle and joint pain and exercise interventions. These strategies are either applied individually or as a combination. These practices have had a remarkable effect on the health care costs while providing a path towards self-healing.

Though many systems of traditional practices have evolved, the Indian and the Chinese traditional systems stand out for their systematic approach to the use of plants and plant products. The Indian traditional system of Ayurveda which regarded the plants such as bitter gourd, turmeric and bael for their medicinal and healing properties, have made their way into the current world. With the advancement of the scientific knowledge and technologies, identification and extraction of plant constituents in their purer from has become possible. Despite the development of modern medicines with a strong scientific base, the WHO estimates that about 80% of the worlds population still relays on the traditional system of medicine.

Botanical perspective

The botanical name of bitter gourd is Momordica charantia. It is also known by other common names such as bitter melon, bitter cucumber, balsam pear, karela and African cucumber. The cultivation of bitter gourd dates back to about 6000 years and hence it is regarded as an ancient world vegetable. Known to have originated in Africa, its domesticated as well as the wild forms spread to the Asian countries in the centuries that followed. Being a tropical plant, it is extensively grown in Asia, India, East Africa and South America.

Though the plant sustains various environmental conditions, hot and humid climate with a temperature range of 25-30 degrees is favorable for the growth of the plant. Cooler temperatures can affect the growth and development whereas frost impacts the survival of the plant. It is regarded as an herbaceous, tendril bearing vine plant that grows to a height of 5 meters bearing yellow flowers. Tendrils are thin, slender thread like structures of a climbing plant. The fruit is oblong shaped with a characteristic rough and warty exterior. The interior of the fruit is hollow with a thin flesh covering the seed cavity. Embedded in the seed cavity are the seeds that are flat.

The fruit is generally eaten when it is green and crunchy. Once it begins to ripen, it is more bitter while the inside of the fruit becomes red and sweet. When fully ripe, it is orange coloured with a mushy texture. It typically splits open as segments which curl back and exposing the seeds covered with bright red pulp. It also exhibits regional variations in the size, shape and appearance. For instance, the Chinese bitter guard is pale green in colour and has a smoother surface compared to the Indian variety.

Nutritional value and chemical composition

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Despite the fact that bitter gourd is a store house of bioactive nutrients, it is not a preferred vegetable due to its taste. In comparison with other members of the gourd family like squash, pumpkin, cucumber and zucchini, it is regarded as a vegetable that is nutritionally dense. It can also be labelled as a weight loss food due to its nutrient profile. The amount of different nutrients present in 100 grams of uncooked bitter gourd are; calories-21, carbohydrates-4 grams, fiber-2 grams, proteins- 1 gram, cholesterol-0, vitamin C- 99%, vitamin A- 44%, folate-17%, potassium-8%, zinc-5% and iron -4% (all expressed as percentage of daily requirements) The description of the different classes of nutrients of bitter gourd are as follows

Carbohydrates

The class of complex carbohydrates called polysaccharides constitute one of the important components of bitter gourd. The extraction of the polysaccharides by using various techniques have revealed that the type of polysaccharide present in bitter gourd are called as heteropolysaccharides. This is a type of polysaccharide made up of different types of sugars that are bonded together rather than a single type of sugar. Some of the sugars that constitute the heteropolysaccharides include galactose, glucose, arabinose, rhamnose and mannose. These have been shown to exhibit an array of biological activities such as anti-oxidant, anti-diabetic, anti-tumor, anti-microbial, immune boosting and neuroprotective properties. They are regarded as one of the key ingredients for medicinal purposes.

Proteins

The seeds of bitter gourd are a store house of high-quality proteins and amino acids (compounds that bond together to form proteins) especially the ones that the body does not produce (also called essential amino acids). As per the recommendations put forth by FAO (Food and Agriculture Organization), WHO and UNU (united Nations University), it is said that these proteins meet the criteria for the amino acid requirement in pre-school children. Some of the proteins that have been extracted from bitter gourd are ribosome inactivating proteins (RIP), Momordica charantia lectin (MCL), Momordica anti-HIV protein (MAP), alpha-momorcharin, beta-momorcharin, gamma-momorcharin, delta-momorcharin and epsilon-momorcharin. These proteins have been shown to exhibit anti-tumour, anti-cancer, anti-microbial and immune protecting activities.

Polypeptide-p is regarded as a type of natural plant insulin or p-insulin that lowers the blood glucose levels. Studies conducted on animals and humans have demonstrated its effectiveness in reducing the blood glucose levels when administered by subcutaneous (beneath the skin layers) injection. Since it resembles the action of insulin in the body, it could probably be given to individuals with type 1 diabetes. This compound has been extracted from the seeds and fruits of bitter melon.

Fats

The seeds of the bitter gourd are a source of oils that make up to 35%-40%. The fatty acids contained in them include monounsaturated fatty acids (MUFA-3.33%), polyunsaturated fatty acids (PUFA-59.96%) and saturated fatty acids (36.71%). The PUFA class of fatty acids include omega-6 and omega-3 fatty acids. The multiple roles played by these fatty acids towards the overall health and well- including the heart health, blood vessel and brain functioning are well acknowledged by several studies. Bitter gourd is one of the sources of conjugated linolenic acid (CLA), a type of PUFA present in mainly meat and dairy products. This has been demonstrated to fight obesity, cancer and atherosclerosis. Studies have also reported the presence of alpha-eleostearic acid, a type of conjugated linolenic acid which has been shown to prevent the growth of cancer cells.

Vitamins and minerals

Bitter gourd is a good source of vitamin C, vitamin A, vitamin E, vitamin B1 (thiamine), vitamin B2 (riboflavin), vitamin B3 (niacin) and vitamin B9 (folate) and beta carotene (an orange, yellow or red pigment present in fruits, vegetables and dark green leafy vegetables that gets converted into vitamin A in the body). It is also rich in minerals like potassium, calcium, iron, magnesium, phosphorous and zinc. Analysis of unripe and ripe bitter gourd have revealed higher vitamin and mineral content in green unripe fruits. Studies comparing the levels of vitamin C in ripe and unripe fruits have demonstrated reduced levels of vitamin C and increased levels of carotene (this explains the yellowish/orange colour of the ripe fruit) associated with ripening.

Saponins

These are naturally occurring organic compounds that are present in plants. They are reported to be present in more than 100 plant families and are an integral component of various plant organs such as roots, stems, barks, leaves and fruits. In plants they are recognised for their protective role against bacteria, fungi, viruses, parasites and insects. Several studies have supported their beneficial role in humans in terms of anti-cancer, anti-inflammatory, anti-microbial, anti-thrombotic, immune strengthening, hypoglycaemic and cholesterol reducing effects. Some of the naturally available plant sources that are rich in saponins include ginseng, horse chestnut, cassava, quinoa, liquorice, caltrop, legumes and oats.

A type of saponin called curcubitanes are recognised for their bitterness. In the bitter gourd plant the saponins are present in the roots, fruits and seeds. The evidence from the pharmacological studies have revealed that the curcubitanes exhibit anti-diabetic and blood sugar lowering properties. Apart from these effects, improved insulin resistance and anti-obesity effects in terms of prevention of weight gain and visceral fat accumulation (fat around the belly and internal organs) have been demonstrated by studies.

One of the important saponins that has gained wide recognition owing to their hypoglycaemic effect is charantin. Recent research has put forth its possible effectiveness as the main treatment for type 2 diabetes with some lines of evidence supporting its efficiency over the anti-diabetic drug tolbutamide. However, a much deeper analysis of charantin is warranted to recognise the particular components that lower the blood sugar in individuals with diabetes.

Terpenoids

These constitute a group of compounds that are naturally present in plants. They impart fragrance, taste and pigment to the plant in addition to defending the plant against harmful microbes and environmental stressors. They also take part in plant growth, photoprotection (protection against harmful effects of the sun) and are regarded as antifeedants (a substance that prevents attack by pests). The terpenoids that are extracted from plants have medicinal value and are used in the treatment of bacterial infections, migraine and malaria. They also have anti-inflammatory, wound healing and cardiovascular protective properties. The terpenoids are one of the key components of essential oils.

Apart from the common plant sources such as tea, thyme, cannabis, Spanish sage and citrus fruits, bitter gourd is also a good source of terpenoids. They are extensively distributed in the stem, leaves and fruits of the plant and exhibit anti-cancer, anti-oxidant, anti-diabetic and blood sugar reducing properties.

Phenolic compounds

These are a type of bioactive compounds that are exclusively present in plants. Being present in all the plant organs, they constitute one of the essential components of the human diet. In addition to protecting the plants against environmental challenges and harmful microbes, they play a key role in imparting the plant colour as well as sensory qualities to the plant foods. They are present in fruits, vegetables, cereals, legumes, chocolates and beverages such as tea, coffee, beer and wine. The major phenolic compounds include phenolic acids, tannins and flavonoids. Among these the flavonoids are present in ample amounts. They have increasingly gained recognition in medical field due to their powerful anti-oxidant effects.

Phenolic compounds and flavonoids constitute one of the chief bioactive components of bitter gourd. They are present in the fruit, seed and pericarp (the part of the fruit enclosing the seeds). Their functions include anti-oxidant, anti-inflammatory and immune system enhancing effects. The medicinal value of bitter gourd is attributed to the presence of high concentration of phenolic compounds. Some of the flavonoids that exhibit anti-diabetic properties are quercetin, rutin, kaempferol, isorhamnetin and genistein.

Sterols

Plant sterols or phytosterols are naturally occurring cholesterol like compounds that are present in plants. Though present in all the plant-based foods, it is acknowledged that vegetable oils (unrefined), nuts, seeds, whole grains and legumes are the rich sources. Some of the fruits and vegetables like navel orange (a type of sweet seedless orange that has a navel like indentation at the tip), tangerine, mango, cauliflower, broccoli, lettuce and peas also contain sterols but not in high amounts compared to the above-mentioned rich sources. Studies have shown that these plant sterols reduce LDL (bad) cholesterol levels by interfering the absorption of cholesterol from the intestines.

Bitter gourd is also regarded as a good source of phytosterols. One of the major phytosterols extracted from the bitter gourd seed oil and fruit is called sitosterol. Studies have reported their effectiveness in reducing the cholesterol levels.

Alkaloids

These constitute organic plant compounds that are particularly present in flowering plants. Their functions are to protect the plant from predators and pathogens as well as regulate plant growth. Alkaloids have a strong foot hold in both traditional and modern systems of medicines due to their enormous healing potential. Some of the plant families that are rich sources of alkaloids include nightshades (tomatoes, peppers, egg plant, potatoes), poppies (colourful flower bearing herbaceous plants), buttercups and amaryllis.

Bitter gourd is also regarded as a good source of alkaloids. Chemical analysis of the bitter gourd has revealed that the alkaloid concentration is high in seeds. The alkaloids present in bitter gourd along with saponins that are released during cooking, contribute to the flavour of bitter gourd. The beneficial effects of some of the bitter gourd alkaloids include anti-diabetic (glycoalkaloids), anti-helminthic (steroidal alkaloids) and anti-bacterial effects. One of the key glycoalkaloid that has been extracted from the seeds of bitter gourd is called vicine. Though there is some evidence supporting its blood sugar lowering effect, more studies are needed to ascertain its safety in treating diabetes.

Medicinal properties

Traditional uses

The bitter gourd plant has been an integral part of traditional and folk medicine for centuries and still continues to hold its place in modern medicine. In the traditional Indian Ayurvedic system of medicine, bitter gourd was known as ‘karela’. The various parts of the bitter gourd plant such as roots, leaves, seeds and unripe fruits were regarded for their health benefits. Its juice was used as a remedy for joint pain, fever, liver and digestive system disorders. The paste from the leaves were locally applied to treat chronic skin diseases, burns, boils and rashes. The whole plant was prescribed as a food and remedy for type 2 diabetes.

The Turkish folk medicine used bitter gourd as a therapeutic and preventive strategy against gastric ulcers. Here the oil was extracted from the ripe bitter gourd and added to sum warmed olive oil and finally blended with honey.

In African folk medicine, bitter gourd is used in the treatment of worm infections, fever, menstrual irregularities, skin diseases and rheumatism. All parts of the plant were used in the treatment of these conditions. The decoction was particularly used to treat type 2 diabetes. In addition, the juice and leaves were used to treat jaundice, liver disease, ulcers and burns. The various plant preparations of bitter gourd were used as a therapy for gonorrhoea, measles, scabies, chicken pox and syphilis.

The Caribbean system of medicine saw the use of leaf decoction and fruit juice for type 2 diabetes. Also, the decoction prepared from the leaf were used as a remedy for hypertension, uterine infections, malaria, dysentery and worm infections. In addition to these, leaf baths were used to relieve the pain and discomfort associated with rheumatism.

Modern view of nutraceutical properties

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Anti-diabetic action

Diabetes mellitus or type 2 diabetes is a common metabolic disorder that has risen to the status of a global pandemic posing a huge public health challenge. The hallmark of type 2 diabetes is insufficient insulin production or insulin action or a combination of both leading to hyperglycaemia or increased blood sugar levels. Insulin is a hormone produced by specialised cells called the beta-cells of pancreas which helps to maintain normal blood glucose levels.

The use of bitter gourd in the treatment of diabetes has a long history dating back to thousands of years. Several studies conducted world-wide have explored the anti-hyperglycaemic (to prevent rise in the blood sugar levels) and hypoglycaemic effect of bitter gourd. Evidence from the animal studies have revealed the benefits of bitter gourd extract in terms of reducing the blood glucose levels, enhancing the insulin production by the beta cells of the pancreas and promoting the restoration of the damaged beta cells.

On the contrary, there is paucity of evidence regarding the anti-diabetic effects of bitter gourd in humans. The first documented human study was conducted by a physician named Lakholia more than six decades back, wherein the study subject was himself. Later on, a study conducted on the evolution of diabetic cataracts revealed that the consumption of bitter gourd fruit extract slowed the cataract formation. Owing to the presence of compounds exhibiting anti-diabetic effect, a number of recent studies have produced convincing results regarding the efficacy of bitter gourd on blood sugar as well as HbA1c levels. Even though bitter gourd looks to be a safe, effective and economical remedy for type 2 diabetes, a much deeper chemical analysis on its composition is needed in order to be applied in clinical practice.

Anti-cancer effects

A growing number of studies have explored the anti-cancer effects of bitter gourd. Though these are the still in the primitive stages, the emerging reports have provided an insight into the anti-cancer activity of bitter gourd. These studies have put forth the role of bitter gourd in preventing the growth of several cancers including cervical, breast, liver, colon, nasopharyngeal cancers and leukaemia. The bitter gourd extract derived from the whole fruit was found to have higher anti-cancer potential and this effect was attributed to the presence of phenolic acids.

In addition to the phenolic acids, certain types of proteins also have been reported to have anti-cancer effects. A protein called lectin has been shown to be protective against nasopharyngeal cancer. Another protein called Momordica anti-HIV protein, prevents the growth and causes apoptosis (cell death) of the cancer cells pertaining to breast, prostate, lung, liver sand brain (glioblastoma). A new protein called BG-4 isolated from the seeds have been shown to prevent the growth of colon cancer. However, there is a need for more extensive studies especially in cancer patients to ascertain this beneficial effect.

Anti-oxidant effects

The phenomenon of oxidative stress occurs as a result of excessive accumulation of harmful substances called free radicals in the body. These highly unstable molecules are either produced as a result of normal cell metabolism or as a result of exposure to pollutants, cigarette smoke, radiation and medications. Generally, they are removed from the body by the action of enzymes and chemicals called anti-oxidants. If there is an imbalance between their production and elimination, excessive amounts get accumulated in the body leading to cell damage. The impact of oxidative stress is the development of never-ending list of illnesses like diabetes, hypertension, obesity, cancer, Alzheimer’s disease, Parkinson's disease, arthritis, and asthma.

Anti-oxidants are compounds that neutralise the harmful effects of free radicals in the body. They are naturally present in fruits and vegetables. Some of the anti-oxidants include vitamin A, vitamin E, vitamin C, carotenoids, phenolic acids etc. Preliminary studies conducted on the anti-oxidant property of bitter gourd have produced promising results. It was found that compared to other vegetables like Colocasia and pumpkin, bitter gourd was superior with regard to its anti-oxidant effects. The evidence from the experimental and animal studies conducted on the effectiveness of bitter gourd polysaccharide extracts have revealed their ability to increase the levels of anti-oxidant enzymes in the body. However, more studies are awaited regarding the individual plant parts for their anti-oxidant effects.

Anti-dementia effects

Neurodegenerative disorders are one of the top 10 causes of death worldwide. They constitute a group of disorders that occurs as a result of damage to the cells of the nervous system that progresses over time affecting their structure and function. The loss of functions includes cognitive skills (higher functions such as memory, thinking, reasoning) and the motor skills (related to movement). The most common neurodegenerative disorders include Alzheimer’s disease and Parkinson’s disease. Though increasing age is considered as a major risk factor, genetics and environmental factors such as exposure to pesticides and toxic metals have been linked to these disorders.

Evidence from experimental studies conducted on the effects of charantin on nerve cell cultures deliberately exposed to damage by selected chemicals, have demonstrated the ability of charantin to maintain the longevity of nerve cells. These effects were attributed to the free radical neutralising ability of charantin. In addition to this, similar studies conducted on bitter gourd polysaccharides have revealed their effectiveness to protect the brain cells against ischaemic injury (a type of injury occurring as a result of reduced blood supply). On the other hand, animal studies have revealed effectiveness of bitter gourd extracts in preventing memory loss. Also, the combination of bitter gourd and lithium chloride (known to reduce the dementia risk) has been found to be potentially effective against Alzheimer’s and could possibly prove to be a preventive measure against the same. However, more studies are needed to apply these findings into clinical practice.

Anti-hyperlipidemic activity

Hyperlipidemia refers to increased lipid or fat level in the blood. The lipids in question include total cholesterol, low density lipoprotein (LDL- good cholesterol), high density lipoprotein (HDL-bad cholesterol), triglycerides, lipoproteins, chylomicrons and apolipoproteins. Elevated blood lipid levels are one of the major risk factors for the development of atherosclerosis as proposed by innumerable studies. Many factors such as obesity, unhealthy life style, excessive consumption of saturated fats, diabetes, hypothyroidism (low thyroid hormonal levels), chronic renal failure etc contribute to increased blood lipid levels.

Studies have investigated the role of the components of bitter gourd plant and its parts in reducing the lipid levels. In one of the animal studies wherein comparative analysis of bitter gourd juice with the cholesterol lowering drug atorvastatin was conducted, it was found that both were equally effective in reducing the total and LDL cholesterol as well as triglycerides. In addition to these findings, it was also revealed that the powder derived from the seeds as well as the whole fruit was effective in reducing the lipid levels. A small increase in the level of HDL (good) cholesterol was also observed. Similar findings were also reported in small studies conducted on humans. Recent studies have put forth the ability of bitter gourd to promote the growth of healthy gut bacteria which is a prerequisite for reducing the lipid levels.

Anti-hypertensive activity

Hypertension can be defined as a medical condition wherein there is persistent elevation of blood pressure. The current cut off values to define high blood pressure is a reading above 130/80 mm hg. However, there is a notion that consistent values above 140/90 mm hg should be taken as a criterion for treatment with the aim of achieving a target blood pressure of 138/80 mm hg. A number of factors including physical inactivity, high salt diet, obesity, excessive intake of alcohol, increasing age and genetics are considered to increase the risk for developing hypertension. Uncontrolled hypertension contributes to the development of stroke, heart attacks, heart failure and kidney failure.

A growing number of studies have explored the blood pressure lowering effect of bitter gourd. Studies conducted on the bitter gourd leaf extracts have revealed their effectiveness in suppressing the activity of an enzyme called angiotensin converting enzyme (ACE). This enzyme helps in the conversion of a hormone called angiotensin-1 to angiotensin-2, which causes narrowing of the blood vessels leading to increased blood pressure. Reducing the activity of ACE is one of the strategies to control blood pressure in clinical practice, wherein medicines called ACE inhibitors are given. Similar action was reported with bitter gourd fruit and seed extracts from experimental and animal studies. A significant reduction in the systolic pressure from 220 mm hg to 180 mm hg was observed.

Anti-microbial activity

An infection that occurs as a result of invasion by a microorganism is called microbial infection. The microorganism in question could be bacteria, virus, fungi etc. They gain entry into our bodies through mouth, eyes, nose, urinary and genital system openings as well as wounds, bites or cuts in the skin. It should be noted that all infections do not lead to disease process. However, the disease occurs when an infected microbe starts multiplying inside the body causing damage to the cells.

Despite the advancements in the fields of science and medicine, natural remedies still have a foot hold in the current times. The role of bitter gourd against infections has been investigated in recent studies. The extract from the leaves has been found to be effective against infections like Escherichia coli, Staphylococcus aureus, Salmonella typhi, Pseudomonas aeruginosa, Klebsiella pneumonia and Candida. This effect was attributed to the presence of alkaloids, flavonoids, saponins, terpenoids and tannins in bitter gourd. Similar effects were observed with bitter gourd fruit and seed pulp extracts. The essential oils extracted from the seeds exhibited anti-microbial activity against Staphylococcus aureus. Also, a compound called plumericin that was extracted from the vine (long, slender climbing stem) was observed to be a powerful anti-bacterial agent compared to the antibiotic cloxacillin.

Anti-viral activity

Human history has witnessed a striking number of deaths from viral infections. There are over thousand types of viruses that affect humans. They are known to infect different tissues and organs such as upper respiratory tract and lungs (e.g., rhinovirus, influenza), colon (e.g., rotavirus), liver (hepatitis B virus), spinal cord (polio virus), blood vessels (ebola virus) and white blood cells (HIV). Owing to the adverse effects of the anti-viral drugs, plant-based products have been increasingly investigated for their anti-viral properties.

Bitter gourd is also one such plant that has been explored for its effectiveness against viruses. Recent studies have found that the extracts from the leaves and stem exhibited anti-viral properties against herpes simplex virus (HSV-1, which is known to cause oral herpes or cold sore) and sindbis virus (SINV, transmitted by mosquitoes causing fever, rashes and joint pain). In addition to the above effects, anti-viral activity against human immunodeficiency virus (HIV), hepatitis B virus and influenza virus has been reported. This feature of bitter gourd is attributed to its chemical composition wherein the activity of a few compounds has been investigated.

A saponin called kuguacin isolated from the root has been shown to exhibit modest anti-viral activity against HIV virus. Similarly experimental and research studies have put forth the effect of a protein called Momordica-anti-HIV protein against HIV virus and its ability to kill the virus infected macrophages and lymphocytes (types of white blood cells). Also, the compound momordicin, a type of saponin has been shown to be protective against Coxsackie virus. This virus is divided into two groups namely A and B and causes hand, foot and mouth disease, pneumonia, myocarditis (inflammation of the heart muscle), meningitis, encephalitis and hepatitis. Analysis of bitter gourd momordicin has shown its ability to protect the cells of the heart muscle that are infected with the virus.

The studies conducted on the effects of bitter melon phytochemicals on Corona virus have regarded them as potential agents to treat Covid infection.

Anti-helminthic activity

Helminthic infection also called as helminthiasis or worm infection is a type of infection caused by helminths. These are the parasitic worms capable of affecting humans and animals. The helminths that are capable of invading the gastrointestinal system are tape worm (cestodes), round worm (nematodes) and flukes (trematodes). These infections are one of the health problems encountered in places with a warm and moist climate coupled with poor hygiene. Despite the availability of the modern medicines, their side effects and drug resistance have become a drawback. Hence the traditional medicines have been regarded as a safe and economical alternative.

Research conducted on the plant parts of bitter gourd including the fruits, seeds and leaves for their anti-helminthic activity have revealed their effectiveness against helminths. Animal studies analysing the effects of bitter gourd extracts have found their ability to paralyse and kill the worms. These effects were linked to the phytochemicals present in bitter gourd. Saponins and alkaloids have been found to be toxic to the worms leading to their paralysis and death. The anti-oxidant effect of the alkaloids prevents the development of the worms in the digestive tract. While the flavonoids interfere with the growth of the larvae, tannins affect the migration of the newly hatched larvae.

Anti-inflammatory activity

It is a well-known fact that the immune system of the body plays an important role in defending the body against invasion by external agents. The invaders in question could be either microorganisms, damaged cells, toxic chemicals or radiation. Inflammation is a type of defensive response that combats with these invaders and hence it is considered to be important for health. When the body gets exposed to any of these agents, an acute or intense inflammatory reaction takes place during which a series of chemical responses at the cellular and molecular level occurs to prevent or minimise the damage to the cells and tissues. This phase is generally followed by renewal of the normal structure and function of the tissue. But, if the ‘acute’ or the ‘intense’ phase goes out of control, it leads to chronic inflammation.

Chronic inflammatory diseases occur as a consequence of long-standing chronic inflammation. Some of the diseases include diabetes, cancer, obesity, heart diseases, arthritis, joint diseases, allergies and asthma.

The term cytokines refer to a group of proteins that are released by various cells of the body in response to an attack by a foreign substance. They are considered as signaling proteins that guide the cells of the immune system to react in instances of danger imposed by a foreign body. The different types of cytokines include chemokines, interleukins (IL), interferons, tumour necrosis factor (TNF) and colony stimulating factor (CSF). These are either pro-inflammatory (promote inflammation) or anti-inflammatory (reduce inflammation). A balance on these two types is needed to reduce the tissue damage and restore normalcy.

Several lines of evidence support the anti-inflammatory effects of plant phytochemicals. Some of the plant derived compounds such as curcumin (turmeric), colchicine (meadow saffron), resveratrol (peanuts, grape vines, red wine), capsaicin (capsicum), quercetin (apples, berries, broccoli, red onions) have been tested in clinical trials and regarded as safe. Emerging evidence from the recent studies have supported the anti-inflammatory properties of the bitter gourd owing to its rich phytochemical content.

A series of animal studies have supported the anti-inflammatory activity of bitter gourd. The administration of the dry powder of bitter gourd has been shown to reduce the inflammation in the fat tissues. Similar effects were noted with the level of pro-inflammatory cytokines. Recent studies conducted on the compounds isolated from bitter gourd have regarded them as potential anti-inflammatory agents against diseases arising from inflammation.

Wound healing property

Wound healing is a complex phenomenon that involves many phases. An efficient coordination between different types of cells, cytokines and the presence of a healthy vascular system (blood vessels) are crucial for a normal healing process. Many factors such as the presence of infection, foreign body, poor circulation, diabetes, obesity, poor nutritional stratus etc. delay wound healing.

The use of natural remedies for wounds has been in practice for many centuries and has witnessed remarkable scientific advancements till the current times. In addition to the long list of natural medicines and herbs that have evolved across centuries, bitter gourd has established its foot hold as a natural healer.

Though the wound healing properties of bitter gourd has been known since ancient times, only recent studies have explored the science behind this effect. Emerging reports from the animal studies have revealed the effectiveness of bitter gourd fruit ointment in promoting the wound healing process especially in the presence of diabetes. An increase the level of a type of cytokine called transforming growth factor-beta (TGF-Beta) which is important for cell growth and multiplication, an essential part of wound healing, was observed. Comparative analysis of conventional creams with that of bitter gourd cream have revealed the superiority of bitter gourd cream in terms of changes related to healing. Recent studies have shown that 1% formulation of bitter gourd cream to be most effective. However, there is a need for human studies in order to apply the wound healing potential of bitter gourd in clinical practice.

Consumption of bitter gourd

The culinary side

Bitter gourd curry Image by mymedblog.org

Crispy bitter gourd Image by mymedblog.org

Bitter gourd is consumed as a vegetable in the tropical and sub-tropical regions of the world. It is extensively used on South Asian, East Asian and South East Asian cuisines. The fruit is commonly eaten as a cooked dish in its unripe (green) or early ripening stage (yellow). Some of the ways by which bitter gourd can be consumed are soups, salads, curries, stir fry, deep fry, boiling, steaming, pickles, snacks, bakery products, stuffed bitter gourd and tea. However, regional variations exist with the recipes.

Toning down bitterness

The bitterness can be removed by soaking the bitter gourd slices in salt water for 15-20 minutes, followed by rinsing and patting them dry. Alternatively, salt can be rubbed on the cut bitter gourd and allowed to rest for 15 minutes. The bitter gourd is gently squeezed for the juices to come out and rinsed in water and dried. The salt marination helps to draw out the bitter juices. Another method is to soak the bitter gourd in dilute yogurt for 30 minutes before cooking. Some of the other ways include scrapping off the skin (especially the rugged surface which has maximum bitterness), soaking the slices in equal parts of water and vinegar with added sugar for 20-30 minutes, blanching and deseeding. If the bitterness persists after cooking, it can be neutralised by adding sugar or jaggery.

Overview of bitter gourd dishes

Bitter gourd soup is generally prepared by blending a combination of ingredients such as onions, tomatoes, ginger, garlic, herbs, salt and spices. In addition to these, chicken, pork ribs, eggs, tofu, noodles, coconut milk and other vegetables like carrots and mushrooms can be added. The stuffed bitter gourd soup is a popular Vietnamese dish wherein the bitter gourd is stuffed with pork or sea food. In the vegan version, a special type of noodles called ‘seitan’ is used along with scallions.

Bitter gourd stir fry can be prepared by seasoning the sliced bitter gourd with spices and herbs. One of the popular Chinese stir fry preparation is cooking bitter gourd with soft scrambled eggs. Here bitter gourd is blanched first followed by scrambling some eggs and combining both with addition of spices.

Crispy Bitter gourd involves marinating the bitter gourd slices with spices followed by deep frying in oil. A proportionate mixture of corn flour, gram flour and rice flour can be used for extra flavour and crispiness. Battered and spiced bitter gourd fritters can either be deep fried or baked. These can be consumed as snacks. Deep frying actually helps in reducing the bitterness.

Bitter gourd salad is prepared by using the grated or sliced bitter gourd and mixing with other vegetables such as sliced onions, tomatoes and cucumber along with seasonings and salad dressings. But given the fact that salad has all the ingredients raw, and bitter gourd as such is not palate friendly, it can be replaced by slices that are salt marinated and deep fried.

Bitter gourd curry is a semi dry dish prepared by cooking sliced or chopped bitter gourd with onions, ground spices, herbs and tempering. Though these are the basic curry ingredients, there are variations to this dish depending upon the region. For a tangier taste, dry mango powder or tamarind paste is added. In Sri Lankan cuisine, coconut milk is added to the curry along with spices.

Bitter gourd pickle is a tangy, spicy dish with a tinge of sweetness that is commonly prepared in India and Nepal. This is a simple and straight forward dish as it involves using the common ingredients in the kitchen such as the mustard seeds, fenugreek seeds, spice powders, garlic, green chillies, sesame/mustard oil and chopped bitter gourd marinated in salt. The use of vinegar is responsible for the tangy taste. At times jaggery is also added which imparts a certain amount of sweetness. Generally, the pickle tastes bitter initially, but after sometime the tagines of the vinegar take over.

Bitter gourd Thepla is a type of Indian flat bread popular in the region of Gujarat. It is prepared by mixing wheat flour and gram flour which is flavoured with spices, ginger and garlic. The grated bitter gourd is added to this and kneaded into a soft dough. The dough is divided into small portions and rolled to a flat bread and dry roasted.

Bitter gourd bakery products include cheese muffins and cupcakes. Here the bitter gourd is finely chopped and marinated with salt. It is then washed thoroughly and added to the baking ingredients which include all purpose flour, baking soda, vanilla extract, salt, sugar, milk, cheese, oil and eggs. The research conducted on the palatability of these products have shown a reasonable level of acceptance.

Stuffed bitter gourd is a type of dish wherein the bitter gourd is either slit longitudinally or cut into thick rings and stuffed with aromatic spices or minced pork along with dried shitake mushroom, carrots or onions. For the minced pork stuffing, light soy sauce or oyster sauce along with salt and pepper are used for seasoning. The stuffed bitter gourd is cooked in a curry sauce or steamed depending upon the culinary practice.

Bitter gourd and potato fry is a popular dish from the region of Bangladesh. The ingredients include finely chopped bitter gourd, finely chopped potatoes, onions, ginger garlic paste, chillies, turmeric powder and salt which are cooked in soybean oil by combining them step by step. The Indian version can be prepared by adding more of aromatic spices and grated coconut.

Bitter gourd tea is a type of herbal drink that is made by using either fresh or dried bitter gourd slices. The tea can also be prepared by using dried leaves of the plant. The first step is to bring about 200 ml water to a boil followed by adding a few slices of bitter gourd. After letting it boil for another 10 minutes, it is allowed to stand briefly so that the contents of the bitter gourd get infused in water. This infusion is strained and consumed. To overcome the bitterness honey or a natural sweetener can be added. However, diabetic people should watch out regarding these additions especially if the tea is consumed to reduce the blood sugar levels.

Value added products

These are defined as raw agricultural products that have been enhanced to increase their market value and shelf life.

Bitter gourd juice and beverages

Bitter gourd juice Image by mymedblog.org

The array of health benefits, particularly the blood sugar lowering effects of bitter gourd juice has been known for long. This appealing drink in terms of nutritional and nutraceutical properties is not wholeheartedly accepted by the human palate for its intense bitter taste. There are some claims about its tendency to cause digestive upset and hypoglycaemia if consumed in excess. But the scientific evidence behind this side effect as well as the safe dosage is scarce. However, as per the Ayurvedic practice, the prescribed dose is generally 2 ml of thick juice mixed with water consumed once a day before food for blood sugar control. Though it has been put forth that a daily dose of 50-100 ml juice or 5 gm of dried fruit thrice a day to be favourable for type 2 diabetes, there is paucity of evidence to validate these doses.

But taking into consideration that it has been a natural, effective, economical and considerably safe remedy for centuries, it is worth trying, preferably with an expert opinion.

It should be noted that one of the differences between bitter gourd tea and juice is that the former is prepared by using either the leaves and/or the fruit while for the later only the fruit is used. Fresh bitter gourd juice can be prepared at home as it is simple and straight froward. After thoroughly washing the bitter gourd, it is cut longitudinally, deseeded and roughly chopped. For 1 cup measure of chopped bitter gourd, half a cup of water is added and blended till smooth. The mixture is strained followed by the addition of salt and lemon juice. As a variation other fruits and vegetables can be added.

In order to make the juice more palate friendly, modified products have been developed on a commercial scale. It has been reported that the addition of potassium metabisulphite (a food preservative that preserves the natural colour of the food in addition to protecting against harmful microbes) made the juice nutritionally more stable compared to adding sodium benzoate. A 15% bitter gourd extract with added artificial sweetener regarded as a functional and dietetic beverage, can be refrigerated and kept for six months without changes in the flavour and nutritional value. Apart from this, ready to serve beverages made with bitter gourd juice, sugar and citric acid, can be refrigerated for up to three months without losing the quality. Juice from other fruits such as lemon, gooseberry etc. can be added to improve the taste and nutritional value.

Fresh bitter gourd products

The shelf life of bitter gourd is only four days when stored at room temperature. However, this can be extended for 3-4 weeks when kept in cold storage at 0-7degrees. The shelf life of fresh-cut bitter gourd slices can be extended by modifying the storage temperature as well as the packaging. It has been put forth that storing at 8 degrees in a low density polyethylene bag extends its shelf-life by 15 days without the nutritional quality getting affected.

Dehydrated bitter gourd products

Dried bitter gourd rings are regarded as versatile products. The main advantages of dried bitter gourd rings are easy storage, packing and lesser overall weight. Just like the fresh ones, they can be used for cooking, stuffing and frying. To prepare them, the bitter gourd fruits are first washed thoroughly and cut into thick rings measuring 1.5 cm. They are then blanched in boiling water for 3 minutes and then soaked in a solution of potassium metabisulphite for 15 minutes. These rings are then spread on an aluminium tray for drying. These can be either solar or cabinet dried (drying in an enclosed chamber). Comparative analysis of these two methods have revealed the superiority of cabinet drying as this method retains higher amount of nutrients.

Dried bitter gourd chips are another useful product that has been analysed for its safety and quality. Research conducted on various soaking techniques have revealed that using 10% sodium chloride prior to air drying produced better quality chips with a longer shelf life compared to using potassium metabisulphite and acetic acid.

Dried bitter gourd powder has been said to be a functional product that is effective in reducing the blood sugar levels. It can be produced by hot-air drying or lyophilization (freeze drying). Research conducted on these two methods has revealed that the bitter gourd powder produced by using lyophilization technique had higher anti-diabetic effect.

Fermented bitter gourd products

Fermented bitter gourd is a simple preparation that uses basic ingredients. The bitter gourd is cut lengthwise and the seeds are removed along with the white flesh. They are cut into thin half-moon shaped slices. The next step is to add one tablespoon of salt into the fermentation jar to which a cup of water (about 236 ml) is added and stirred. This is followed by adding the cut bitter gourd slices into the jar containing salt water. The bitter gourd slices are stirred with a spoon so that they get evenly distributed in the jar. The next step is to push down the slices so that they are fully submerged in the salt water. The jar is closed and left to ferment for 3-5 days. The fermented bitter gourd has a sour, pungent and bitter flavour. Along with bitter gourd other vegetables like bell peppers, onions and carrots can be added.

Fermented bitter gourd juice is prepared by adding a bacteria called Lactobacillus fermentum to the bitter gourd juice. Recent studies have revealed that fermented bitter gourd juice has a higher antioxidant and blood sugar lowering properties compared to the non-fermented juice. In addition to these findings, the juice is said to have probiotic potential.

Safety profile

Generally, the plant and its products are regarded as safe for consumption. The bitter gourd extracts that are available as supplements over the counter in the form of tablets, powders and liquids, are usually well tolerated. The recommended dose for the tablet is 500-1000mg taken twice or thrice daily. For the powder it is one teaspoon twice daily. However, at times there may be some unwanted side effects and this depends on the individuals physical state, type of product, processing methods etc.

Some of the side effects encountered include abdominal discomfort, nausea, vomiting, diarrhoea, constipation, headache, dizziness and hypoglycaemia. It is considered as an abortifacient and hence pregnant women or women who are trying for a pregnancy should avoid them. For safety reasons, breastfeeding mothers should avoid karela though the scientific evidence behind this is insufficient.

In diabetic people precautions have been advocated regarding the possibility of hypoglycaemia when combined with anti-diabetic drugs. Evidence from the animal studies have revealed that a combination of metformin and bitter gourd to be more efficient as an anti-diabetic rather than individualised treatment. However, it is advisable to take an expert opinion before consuming bitter gourd products especially in the presence of a vulnerable situation.

Summary

*The traditional system of medicine has a long history dating back to 60000 years and continues to hold a special therapeutic value in the current times.

*The botanical name of bitter gourd is Momordica charantia.

*The fruit typically has a rough and warty exterior with a thin flesh covering the seed cavity.

*It undergoes change in the colour, texture and bitterness during the ripening process.

*There are regional variations in the size, shape and appearance of the fruit.

*Bitter gourd is regarded as a power house of nutrients containing complex carbohydrates, proteins, fats, vitamins, minerals, saponins, terpenoids, sterols, phenolic compounds and alkaloids.

*The bioactive ingredients have an array of health benefits.

*The components of bitter gourd namely polypeptide-p, charantin and vicine are responsible for their hypoglycaemic effects.

*Bitter gourd has been a part of traditional and folk medicine for many centuries.

*The juice and decoction were used as a remedy for type 2 diabetes, fever, joint pain, liver and digestive system disorders, skin diseases and menstrual irregularities in different systems of folk medicine across the world.

*Scientific research has provided more insights into the nutraceutical properties of bitter gourd.

*In the modern world, the clinical application of bitter gourd in the treatment of type 2 diabetes warrants more research.

*The evidence behind the anti-cancer activity of bitter gourd is in the primitive stages.

*Available lines of evidence have revealed the potential of bitter gourd to prevent the growth of cervical, breast, prostate, lung, liver, colon, nasopharyngeal cancer and leukaemia.

*Bitter gourd is regarded as a superior anti-oxidant, though more studies are awaited.

*The charantin and polysaccharides of bitter gourd have been shown to have neuroprotective potential.

*Bitter gourd juice has been said to be equally effective as atorvastatin in reducing the cholesterol levels.

*The extracts from the leaves, fruits and seeds have been found to have the potential to suppress the activity of angiotensin converting enzyme, thus causing a reduction in blood pressure.

*The essential oils from the seeds, fruit and leaf extract offer protection against various bacterial and fungal infections.

*Plumericin, a compound isolated from the vine of the bitter gourd plant is considered to be as efficient as the antibiotic cloxacillin.

*Studies have supported the anti-viral properties of bitter gourd against herpes simplex virus, sindbis virus, HIV, hepatitis B virus, influenza, coxsackie and coronavirus.

*Compounds like kuguacin, Momordica anti-HIV protein and momordicin have been shown to possess anti-viral properties.

*The anti-helminthic activity of the bitter gourd is attributed to the various phytochemicals.

*Saponins, alkaloids, tannins and flavonoids have been shown to cause paralysis and death of the helminths in addition to interfering with the larval development and migration.

*The compounds of bitter gourd have been regarded as potential anti-inflammatory agents against diseases that occur as a result of inflammation.

*Bitter gourd has been regarded as a natural wound healer since ancient times.

*Though the current scientific evidence supports the wound healing properties of bitter gourd, human studies are warranted for application in clinical practice.

*Bitter gourd is extensively used in South Asian, South East Asian and East Asian cuisines.

*Some of the dishes include soups, stir fry, salad, curries, baked products, snacks, pickles and bitter gourd tea.

*The value-added products include bitter gourd juice and beverages, dried and fermented products.

*There are variations regarding the dose of bitter gourd juice and the suggested doses need to be validated scientifically.

*Fermented bitter gourd products have been shown to be more efficient in their anti-oxidant and anti-diabetic effects.

*Fermented bitter gourd juice has been shown to have probiotic potential in recent studies.

*Bitter gourd plant and its products are regarded as safe to consume though some side effects have been reported in certain individuals.

*It is advisable to consult a health care professional regarding the safety profile of bitter gourd and its products especially in vulnerable situations.