Abstract

The increasing prevalence of diabetes mellitus is gradually becoming a public health threat globally. Most existing therapeutic regimens are not without limitations and constraints, hence, the need for easy, feasible and cost effective alternative cannot be overemphasized. Some herbs and spices have been observed to exert antidiabetic activity. This review therefore compiles antidiabetic herbs and spices with the places of origin, conditions for growth, culinary uses and mechanisms of action of the antidiabetic effect with a view of encouraging their possible use as an antidiabetic food adjunct in cuisines towards the prevention and management of the diabetes. The search engines accessed were Google Scholar, Scopus, HINARI and PubMed. Antidiabetic herbs and spices compiled include; African nutmeg, Basil, Cinnamon, Cloves, Coriander, Cumin, Curry leaves, Dandelion, Dill, Fenugreek seeds, Garlic, Ginger, Mustard seed, Nutmeg, Onion, Rosemary and Turmeric. Some of these are most suitable only in savoury dishes while others are applicable in both sweet and savoury dishes. The possible mechanisms of the antidiabetic activity are: inhibition of the activities of α-amylase, α-glucosidase, hexokinase, Dipeptidyl peptidase-4 (DPP-4), glycogenolytic and gluconeogenic enzymes; activation of antioxidant enzymes, Adenosine monophosphate-activated protein kinase (AMPK); free radical scavenging activity; mimicry of insulin action; enhancement of insulin secretion; enhancement of Glucose transporter-4 (GLUT-4) translocation and antiplatelet activity. Some herbs and spices are indeed antidiabetic. However, their application in cuisines could be an easy, feasible and cost effective measure to prevent and manage diabetes globally.

1. Introduction

The prevalence of diabetes mellitus, which has been identified as a ‘”disease of comfort” or “civilization disease”, is increasing globally. The global prevalence of diabetes among all age groups was estimated to be 2.8% (equivalent to 171 million people) in 2000 and this was projected to increase to 4.4% (equivalent to 366 million people) in 2030 ¹. The reports of Shaw et al, ² and Whiting et al., ³ corroborated this. The global prevalence of diabetes among adults between 20-79 years was 6.4% (285 million adults) in 2010 and this was projected to increase to 7.7% (439 million adults) in 2030 ² while in 2011 there were 366 million people (all age groups) with diabetes and this was expected to rise to 552 million in 2030 ³.

Existing diabetic therapeutic regimens are known not to be without limitations some of the undesireable side effects of which include weight gain ⁴, hypoglycaemia risk or shock ⁵, dyspepsia, nausea, vomiting ⁶ amongst others.

For culinary use herbs and spices are included in food to enhance flavour, colour, appearance, taste and sometimes texture of the food. If the part of the plant used are the leaves it is called a herb while it is a spice if other parts such as roots, barks or seeds are used. Exploration of the culinary use of antidiabetic herbs and spices may be an easy, feasible and cost effective alternative to prevent and manage diabetes throughout the world. This review therefore compiles the origin, growth conditions, culinary uses and mechanisms of action of some antidiabetic herbs and spices with a view of encouraging their use in cuisines towards reducing the prevalence of diabetes globally.

2. Methodology

The search engines accessed included Google Scholar, Scopus, HINARI and PubMed.

African nutmeg also known as calabash nutmeg is a native of evergreen forests of West and Central Africa. The seeds are used as spice in both savoury and sweet dishes ⁷. It is commonly seen grown wild in evergreen forest and it does not always produce fruit when cultivated because of the unavailability of the beetle that normally pollinates them in the wild ⁸. The inhibitory effect of ethanolic extract of African nutmeg on α-amylase is one of the possible mechanisms of its antidiabetic activity; hence, it may reduce glucose digestion and subsequently lowers postprandial glucose ⁹.

Basil is native to tropical Africa and West South East Asia and is now cultivated in different parts of the world that favour its growth. Basil is sensitive to cold and grows best in hot, dry conditions, hence, it may be cultivated in temperate zones and sub-tropical climates. The leaves are used as culinary herbs mostly in savoury dishes but when steeped in cream or milk may be applicable in ice cream and similar cold desserts. It is commonly added as the last ingredient due to the volatility of its aromatic flavour. It complements beautifully with onion, garlic and olives ¹⁰. The antidiabetic effect of Basil is exerted via enhancing the translocation of Glucose transporter-4 to plasma and cell membranes ¹¹ and inhibition of α-glucosidase and α-amylase activities ¹².

Cinnamon is obtained from the bark of several tree species of the genus Cinnamomum and ground into powder to be used as spice. Cinnamomum verum is sometimes considered to be the true cinnamon. It is native to Ceylon in Sri Lanka but now Indonesia, China, Vietnam and Burma are notable producers. Humid tropical evergreen rainforest conditions with well-drained, sandy soil rich in humus best favours the growth of cinnamon. Cinnamon is of wide application in cuisines and is mostly suitable for both savoury and sweet dishes. A possible mechanism of the antidiabetic activity of cinnamon is via the inhibition of α-amylase, α-glucosidase and lipase activities ¹³ while cinnamon (Cinnamomum zeylanicumon) powder supplementation in diet increased the activity of antioxidant enzymes (Glutathione peroxidise, catalase and superoxide dismutase) thus preventing diabetic complications due to diabetes-induced oxidative stress in alloxan-induced diabetic rats ¹⁴.

Cloves are native of Maluku Islands in Indonesia and are the aromatic flower buds of a tree of the family Myrtaceae. Cultivation requires humid tropical and sub-tropical climatic conditions with optimum temperature of around 70-85°F (20-30°C). It is applicable in most savoury and sweet dishes ¹⁵. The antidiabetic effect of clove is traceable to its ability to inhibit the activity of α-amylase markedly (T16) while clove aqueous extract lowered blood glucose via mimicry of insulin action and inhibition of the activities of phosphoenol pyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) through reduction of gene expression ¹⁷.

Coriander is an annual herb native to Southern Europe and North Africa. It can grow well in both temperate and tropical frost-free climates, does not grow well in heavy clay soil and does not need much fertilizer ¹⁸. For culinary purposes, the leaves are used as garnishes and culinary herbs in most savoury dishes while the seeds are used as spice in sweet dishes. Ethanolic extract of coriander leaves was observed to restore viability of destroyed pancreas in alloxan-induced diabetic mice while it inhibited the activity of α-glucosidase in vitro ¹⁹. Coriander seeds reduced elevated biomarkers of metabolic syndrome and artherosclerosis and increased cardio-protective indices in obese hyperglycaemic-hyperlipidemic Meriones shawi rats ²⁰.

Cumin is a native of Iran and the Mediterranean. It is grown in cooler climates in spring and requires fertile, well-drained soil. It is used as spice in many savoury dishes and is a staple ingredient in curry powder and many spice blends. The antidiabetic effect of cumin seeds was exerted through enhancement of insulin secretion and the amelioration of diabetes-induced oxidative stress by exhibiting free radical scavenging activity in streptozocin-induced diabetic rats ²¹.

Curry tree is native to India. It is a tropical and sub-tropical plant and the cultivation has spread to different parts of the world suitable for its growth. The leaves are mostly used as culinary herbs in savoury dishes. Aqueous extract of curry leaves restored the viability of the degenerated kidney and Islets of Langerhans in streptozocin-induced diabetic rats thus lowering blood glucose and improving weight gain ²². In the same vein, Gangwar and Rao, ²³ reported the antidiabetic effect of powdered curry leaves which was achieved via inhibition of hexokinase, glucose-6-phosphatase and fructose 1,6-bi phosphatase activities, enhancement of insulin secretion and C-peptide resulting into reduced blood glucose and glycated haemoglobin.

Dandelion is a large genus of flowering plants in the family Asteraceae. It is native to Eurasia and North America. It is a hardy, short-lived perennial that is capable of growing anywhere regardless of soil conditions and is found growing in many temperate regions of the world. The leaves are used as culinary herbs in savoury dishes, garnishes, accompaniment, salads and wine production while the flowers can be processed into jam ²⁴. Different isolates of Taraxacum officinale exhibited inhibitory effect on α-glucosidase in vitro ²⁵ as well as α-amylase ²⁶.

Dill is an annual herb in the celery family Apiaceae. It is native to Mediterranean region and Russia. It grows best at soil temperature of between 60-70°F (15-22°C) and requires rich soil. Dill leaves are used as culinary herbs while the seeds are used as spice mainly in savoury dishes but sometimes in some milk and yoghurt dishes. Aqueous extracts of dill leaves and seeds prevented diabetic complication and ameliorated diabetic state via free radical scavenging activity, prevention of the formation of advanced glycation end products (AGEs) and fructosamine as well as the reduction of protein carbonyl and thiol groups oxidation ²⁷.

Fenugreek is a fragrant annual plant of the family Fabaceae, It is native to southern Europe and the Mediterranean region. The most suitable growing conditions for fenugreek are warm to hot climate with temperature range of 50-90°F (10-32°C) and for optimum seed production it is advisable to grow it in spring or early summer ²⁸. Its fragrant leaves are used as culinary herbs while the aromatic flavourful seeds are applicable as spice mostly in savoury dishes. The seed powder is also a staple ingredient in curry powder, many spice blends and tea blends ²⁹. Many scientific studies have established the antidiabetic effect of fenugreek and this was channelled through the inhibition of pancreatic lipase and α-amylase activities ^{30, 31}, notable free radical scavenging activity as well as enhancement of glucose uptake by 3T3-L1 cell lines ³².

Garlic is native to Central Asia. Extremely high temperatures are not suitable for garlic growth and the optimum temperature range for growth is 12-34°C in fertile, well-drained light soil (clay should be avoided) ³³. The pungent flavour of garlic cloves makes it only suitable for savoury dishes. Inhibition of the activities of angiotensin-converting enzyme, α-amylase and α-glucosidase as well as notable free radical scavenging activity ³⁴.

Ginger originated from Southern Asia. It is now cultivated in different parts of the world suitable for its growth. The optimum conditions for ginger growth is warm and humid climate in well-drained soils such as sandy, clay, red loam, lateritic loam and friable loam which is rich in humus. Fertility is a necessary soil requirement ³⁵. It is of interest to note that the culinary use of ginger is versatile since it is applicable and suitable for almost all dishes both savoury and sweet. Ginger exerts its antidiabetic effect via enhancement of insulin secretion ³⁶ and mimicry of insulin action in enhancing glucose uptake by the muscle and adipose of normal and diabetic rats ³⁷.

Mustard is a native of tropical regions of North Africa, temperate regions of Europe and some parts of Asia. It is an annual plant best cultivated in well-drained soil and thrives well in sandy and loam soil with varying pH from acid, neutral to alkaline (4.9-8.2). It can even grow in high acid soil and is adaptable to a wide variety of climatic conditions with temperature range 6-27°C ³⁸. The seed is used as spice and condiment mostly in savoury dishes. The possible mechanism of the antidiabetic effect of mustard seed is via activation of glucose synthetase thus enhacing glycogenesis, inhibiting the activity of gluconeogenic enzymes and glycogen phosphorylase thus reducing hepatic production of glucose ³⁹. Another possible mechanism of action is by enhancing insulin secretion ⁴⁰.

Nutmeg is native to the Spice Islands (Moluccas) in Indonesia. It is a tropical evergreen tree belonging to the family Myristicaceae. Nutmeg thrives well in tropical climate with humid conditions, temperature range 77-95°F (25-35°C), not less than 60 inches annual rainfall and clay loam, sandy loam and red laterite soil. It can be propagated both sexually and asexually ⁴¹. Two spices can be derived from the fruit; nutmeg from its seed and mace from the seed covering but the former is more popular in use than the latter. Nutmeg is applicable in many kinds of baked foods, confections, puddings, meat sausages etc; hence, it is suitable for many savoury and sweet dishes. Mace is similar to nutmeg in its culinary uses. The blood glucose lowering effect of nutmeg was achieved by improving insulin sensitivity via functional activation of peroxisome proliferator-activated receptors (PPARs) which enhanced 3T3-L1 preadipocytedifferentiation, regulation of target genes and protein expression and enhancing GLUT-4 translocation (42).

Onion is a biennial plant belonging to the family Amaryllidaceae. It is native to Southwest Asia and is now grown worldwide in places suitable for its growth. It does not thrive well in regions with excessive heat, cold and rainfall but grows under a wide range of climatic conditions. The bulb is versatile in use in savoury dishes and it also tenderises food. The antidiabetic effect of onion has been established by various scientific reports and the possible mechanism of action is by its markedly notable antioxidant and antiplatelet aggregation activities thus preventing diabetes complication ⁴³ as well as inhibition of the activity of α-glucosidase and free radical scavenging activity ³⁴.

Rosemary is a perennial herb related to the mint or Lamiaceae family. It is native to the Mediterranean regions and thrives well in warm and moderately dry climates with average temperature range 68-86°F (20-30°C. It needs at least 6-8 hours of daily sun exposure ⁴⁴. The needle-like leaves are used as culinary herbs mainly in savoury dishes specifically meat, poultry, fish and related food products. A notable mechanism of the blood glucose lowering effect of rosemary is on its ability to regulate incretins which are hormones that augment secretion of insulin after food consumption thus enhancing glucose uptake and lowering hepatic blood glucose. Rosemary exerts inhibitory action on Dipiptidyl peptidase-4 (DPP-4) which breaks down incretins and makes them available to serve their purpose in the body ⁴⁵ Another possible mechanism of action is the activation of 5’ Adenosine monophosphate-activated protein kinase (5’AMPK) which enhances glucose uptake in skeletal muscle thus improving insulin sensitivity ⁴⁶.

Turmeric was believed to have originated from Southern East Asia.It belongs to the ginger family which is Zingiberaceae. It is a tropical rhizomatous, herbaceous perennial plant. Optimum temperature for growth is between 68 and 86°F (20 and 30°C) and it requires warm and humid climatic conditions, annual rainfall of at least 1500mm and does not thrive well in water stagnation and alkalinity ⁴⁷. The root is use as spice in cooking exerting a mustard-like, pungent and earth aroma. It is suitable for savoury and sweet dishes while the leaves are used only in sweet dishes ⁴⁸. The high potency of turmeric in free radical scavenging activity is markedly one of the possible mechanisms of its antidiabetic activity, hence, it may prevent diabetes complications which may result from diabetes-induced oxidative stress ⁴⁹. Furthermore, it also exerts inhibitory effect on α-amylase activity ⁵⁰.

3. Conclusion

The herbs and spices compiled are indeed antidiabetic food adjuncts and the culinary application of these may be an easy, feasible and cost effective measure to prevent and manage diabetes globally.

References