Here is a list of foods which have been studied extensively confirming their anti-diabetic properties.
1. Fenugreek (Trigonella Foenum Graecum):
Consumption of fenugreek seeds has been a traditional dietary advice to diabetics for the control of blood glucose level. Available data suggest that though several anti-diabetic plants of Iran need further study, the best evidence in glycaemic control was found in Citrullus colocynthus, Ipomoea betatas, Silybum marianum and Trigonella foenum graecum.
The action of fenugreek in lowering blood glucose levels is almost comparable to the effect of insulin. In a majority of patients, a mild improvement in clinical symptoms such as polydipsia and polyuria were observed along with a reduction in anti-diabetic drug doses. Extensive research provided the scientific basis for the mechanism of anti-diabetic action of fenugreek seeds.
The gel forming characters of fenugreek fiber reduces gastric emptying, glucose absorption and the insulin response. The soluble dietary fiber (SDF) fraction of fenugreek seeds exerts anti-diabetic effects mediated through inhibition of carbohydrate digestion and absorption, and enhancement of peripheral insulin action.
Ali et al. (1995) had confirmed the involvement of the major constituent of SDF fraction, a galactomannan in the hypoglycaemic effect. Besides SDF, a novel amino acid 4-hydroxyleucine present in fenugreek seeds was found to increase glucose stimulated insulin release by isolated islet cells in both rats and humans.
In addition to decreasing blood glucose level, administration of fenugreek seeds also normalized creatinine kinase activity in heart, skeletal muscle and liver of diabetic rats besides reducing hepatic and renal glucose-6-phosphatase, and fructose 1, 6-biphosphatase activity. Fenugreek extract lowered kidney/body weight ratio, blood glucose, blood lipid levels and improved hemorheological properties in experimental diabetic rats following repeated treatment for 6 weeks.
The extract exhibited hypo-lipidemic action in addition to hypoglycaemic effects in the streptozotocin-induced diabetic rats. Fenugreek also showed anti-oxidant potential to protect the organs such as liver and pancreas against the oxidative damage induced by diabetes, apart from controlling the blood glucose levels.
The hypoglycaemic response of fenugreek seemed to be dose dependent. Animal studies proved that an oral administration of 2 and 8 g/kg of fenugreek plant extract produced dose dependent decrease in the blood glucose levels in both normal as well as diabetic rats and appropriate dose of fenugreek administration has been proposed for diabetic patients.
Incorporating around 25g fenugreek seeds in the daily diet can serve as an effective supportive therapy in the management of diabetes. Not only a significant reduction in blood glucose but also a significant reduction in cholesterol, triglycerides and urinary sugar levels was observed on consumption of fenugreek.
The most effective dose recognized was 1 g/kg body weight but that is still lower than the standard anti-diabetic drug. No acute or delayed toxicity was observed with ethanol extract of methi seed when it was administered orally at a high dose level of 3 g/kg body weight, which is higher than effective anti-hyperglycemic dose. Interestingly, addition of fenugreek to vanadium significantly removed the toxicity of vanadium when used to reduce blood glucose levels.
2. Jamun (Eugenia Jambolana):
Jamun commonly known as Jambolan or Black Plum is found throughout the plains. Jamun was one of the significant anti-diabetic plants and it has long been reported for its use in many pharmacological conditions mainly diabetes. During the last four decades, numerous folk medicine and scientific reports on the anti-diabetic effects of this plant have been cited in the literature.
Clinical and experimental studies suggest that, different parts of the plant especially fruits, seeds and stem bark possess promising activity against diabetes mellitus. The folkloric practice was consumption of juice extracted from the jamun leaf mixed with honey or cow’s milk, or fresh fruits consumed twice a day orally after food for 3 months. Jamun seed extract (JSEt) has also been shown to possess hypo-glycaemic action.
The decrease in thiobarbituric acid reactive substances (TBARS) and increase in reduced glutathione (GSH), superoxide dismutase (SOD) and catalase (CAT) clearly showed the antioxidant property of the JSEt. The effect of JSEt was most prominently seen in the case of animals given 5.0 g/kg body weight. JSEt was more effective than glibenclamide.
Anti-hyperglyceamic effect of aqueous and alcoholic extract as well as lyophilized powder shows reduction in blood glucose level. The hypoglycaemic activity of jamun pulp extract in streptozotocin induced diabetic mice was seen within 30 min of administration while the seed of the same fruit required 24 h.
The oral administration of the extract resulted in increased serum insulin levels in diabetic rats. Insulin secretion was found to be stimulated on incubation of plant extract with isolated islets of Langerhans from normal as well as diabetic animals. These extracts also inhibited insulinase activity from liver and kidney thus delaying the inactivation of insulin in the body. The elevated levels of cholesterol, phospholipids, triglycerides and free fatty acids were restored to near normal by jamun kernel or glibenclamide treatment in streptozotocin induced diabetic rats.
Ravi et ah (2004a; 2004b; 2005) concluded that Jamun kernel possesses hypo-lipidemic effect, which may be due to the presence of flavonoids, saponins, glycosides and triterpenoids in the extract. Thus the efficacy of Eugenia jambolana seed kernel in the amelioration of diabetes may be attributed to its hypoglycaemic property along with its anti-oxidant potential of the seed kernel which also compared well with glibenclamide, a standard hypoglycaemic drug.
Ravi et ah (2004 c) confirmed that the inorganic constituents play an important role in the antidiabetic nature of jamun seeds. The ethanolic extract of dried jamun seed kernel (200 mg/kg) showed anti- hyperglyceamic effect on 10th day of its administration. There was a decrease in cholesterol level with little or no effect on triglycerides level. Interestingly, the extract was not only effective in reversing the increased propensity to ulceration in diabetic rats but also decreased the acid-pepsin output better than glibenclamide.
Hence, Chaturvedi et ah (2009a) observed the ulcer protective effect of jamun was due to its anti-diabetic and gastric anti-secretory effects. Because of its both anti-hyperglycemic and mucosal defensive actions, it could be a better choice for treating gastric ulcers co-occurring with diabetes Chaturvedi et ah (2009b). Sridhar et ah (2005) also observed the anti-diabetic effect of jamun seed powder with an oral dose of 500 mg/kg. Sub-acute toxicity studies with a single administration of 2.5 and 5.0 g/kg seed powder showed no mortality or abnormality.
3. Barley:
The ancient Hindu physician, Charaka had identified barley as a low glycemic dietary substitute for diabetic patients around 2800 years ago. He also advocated different invigorating agents like honey, triphala and vinegar for use with barley- based diet and drink. Barley and its various products have been reported to possess preventive and therapeutic anti-diabetic properties, both in experimental animals and clinical studies.
Naismith et al (1991) reported that barley reduced blood glucose level, water consumption and weight loss. Mahdi et al (1994) observed that substitution of barley for sucrose reduced the elevated plasma concentration of 7-S collagen and of laminin P2, peptide fragments that retain antigenicity of the parent proteins. It is suggested that the beneficial property of barley is due to its high content of chromium.
Malted barley extract alleviated many of the symptoms of diabetes in genetically obese mice and thus can be a good supplement for normalization of blood glucose levels in humans. Li et al (2003a) demonstrated that barley enabled glycemic control and improved glucose tolerance compared with rice or alpha-corn starch. Barley diet significantly improved the area under the plasma glucose concentration time curves, lowered the fasting plasma glucose and glycosylated hemoglobin levels, and decreased plasma total cholesterol, triglycerides and free fatty acid levels.
Reports are available with barley administration on low glyceamic index and high insulinemic index, significant improvement in glycemic and insulinemic indices, improvement in glyceamic response and insulinemic response, reduced dependence on oral hypoglycemic drugs and improvement in impaired carbohydrate and lipid metabolism.
However, no significant change in total cholesterol, HDL- cholesterol, triglycerides or in fasting and postprandial blood glucose level was also observed by Keogh, (2003). This lack of effect may be, at least in part, a consequence of structural changes in β-glucan that result from the commercial processing of the barley into a highly enriched β-glucan product or from the freezing, storage, or baking of the product during the intervention period.
Reduction in postprandial glycemic peak with better insulin response, glycemic and insulinemic response and overall metabolic improvement in patients were also noticed. The therapeutic benefits of barley made it suitable for its selection as a dietary substitute and inclusion of other fortifying agents in barley based diet and drink.
4. Honey:
Charaka Samhita emphasized that honey should also be taken along with various food preparations made up of barley. Animal experiments and observations made in normal human volunteers, type- I diabetic patients type-II diabetic patients, and in young adults with impaired glucose tolerance showed that honey attenuates postprandial hyperglycemic response and hence may serve as a suitable sugar substitute for diabetics.
5. White Beans (Phaseolus Vulgaris):
White bean pods are among the most widely used traditional remedies against diabetes mellitus. Venkateswaran and Pari (2002) found oral administration of Phaseolus vulgaris pod extract (200 mg/kg body weight) for 45 days to result in a significant reduction in thiobarbituric acid reactive substances and hydroperoxides. The extract also causes a significant increase in reduced glutathione, superoxide dismutase, catalase, glutathione peroxidase and glutathione-S-transferase in the liver and kidneys of rats with streptozotocin-induced diabetes.
Apart from significant reduction in the elevated blood glucose, serum triglycerides, free fatty acids, phospholipids, total cholesterol, very-low-density lipoprotein cholesterol, and low- density lipoprotein cholesterol the extract also caused a significant decrease in plasma thiobarbituric acid-reactive substances (TBARS), hydroperoxides, vitamin E, and ceruloplasmin. The decreased serum levels of high-density lipoprotein cholesterol, anti-atherogenic index (AAI), plasma insulin, vitamin C, and glutathione in the diabetic rats were also reversed toward normalization.
The administration of Phaseolus vulgaris pods (PPEt) to diabetic animals normalized blood glucose and resulted in a marked improvement of altered carbohydrate metabolic enzymes during diabetes. The effect at 200 mg/kg of body weight was better than that of glibenclamide. Because of their fiber content and an alpha-amylase inhibitory effect, beans might be more useful as food components in preventing or ameliorating type 2 diabetes.
6. Banana (Musa Sapientum):
Musa sapientum (‘Ney Poovan’) commonly known as ‘banana’ is mainly used in Indian folk medicine for the treatment of diabetes mellitus. Oral administration of 0.15,0.20 and 0.25 g/kg of chloroform extract of the Musa sapientum flowers (MSFEt) for 30 days resulted in a significant reduction in blood glucose, glycosylated haemoglobin and an increase in total hemoglobin, but in the case of 0.25 g/kg dose, the effect was highly significant. It also prevented weight loss.
7. Amla (E. Officinalis):
Amla works by stimulating pancreas in diabetics. Though E. officinalis have been reported to possess beneficial anti- diabetic properties by various mechanisms, the homogeneous hypoglycaemic activity could be achieved only by the use of triphala Methanolic extract (75 per cent) of Terminalia chebula, Terminalia belerica, Emblica officinalis and their combination named ‘Triphala’ (equal proportion of above three plant extracts) are being used extensively in Indian system of medicine.
Oral administration of the extracts (100 mg/kg body weight) reduced the blood sugar level in normal and in alloxan (120 mg/kg) diabetic rats significantly within 4 hours. Continued, daily administration of the drug produced a sustained effect.
8. Bilva Bael Fruit/Bengal Quince, Bel or Bilva (Aegle Marmelos):
Aegle marmelos extract effectively reduced the oxidative stress induced by alloxan and produced a reduction in blood sugar. Kesari et al. (2006) showed that the aqueous extract of bel seed (250 mg/kg) reduced the fasting blood glucose by 61 per cent and urine sugar by 75 per cent from their pretreatment levels. It brought about fall in the level of total cholesterol (TC) by 25 per cent with increase of 33 per cent in high density lipoprotein (HDL) and decrease of 54 and 46 per cent in low density lipoprotein (LDL) and triglyceride (TG), respectively in diabetic rats.
The histopathological study by Kamalakkannan and Prince (2005) on the bel fruit extract treated groups showed improved functional state of the pancreatic ss-cells and partially reversed the damage caused by streptozotocin to the pancreatic islets. The extract of A. marmelos modulates the activity of enzymic and non-enzymic antioxidants and enhances the defense against reactive oxygen species-generated damage in diabetic rats.
Abraham et al. (2010) demonstrated that the pyridoxine treatment alone and in combination with insulin and A. marmelose had a role in the regulation of insulin synthesis and release, normalizing diabetic related oxidative stress and neuro-degeneration affecting the motor ability of an individual by serotonergic receptors through 5-HT (2A) function.
Bhatti et al (2011) showed that-the ethanol extract of bel leaves attenuated the severity of the condition and improved the myocardium in the early stages of alloxan- induced diabetic cardiomyopathy at a dose of 200 mg kg(-1). Sharma et al (2011) reported that the protective effect of fruit aqueous extract in type 2 diabetic rats is due to the preservation of β-cell function and insulin-sensitivity through increased PPARγ expression.
Methanol extract of the bark of Aegle marmelos at 200 and 400 mg/kg showed significant reduction in blood glucose level by 19.14 per cent and 47.32 per cent, respectively in diabetic rats. It also significantly increased insulin level, and produced similar effects on other biochemical parameters. Histological studies showed the regenerative effect on the β-cells of diabetic rats. Immuno-histochemical observations in the extract treated diabetic rats showed increased insulin-immuno-reactive β-cells.
9. Gurmar (Gymnema Sylvestre):
The Hindi word Gur-mar, Madhunaashini in Sanskrit, Chakkarakolli in Malayalam, Podapatri in Telugu, literally means sugar destroyer. Extracts of this plant are widely used in Australian, Japanese, Vietnamese and Indian folk medicine. Gymnema preparations have a profound action on the modulation of taste, particularly suppressing sweet taste sensations. It is used in the treatment of diabetes mellitus and in food additives against obesity and caries. Anti-allergic, antiviral, lipid lowering and other effects are also reported.
The EtOH/H2O extracts of the leaves of gurmar were shown to be able to inhibit glucose absorption in rats. Supplementation of the diet with G.sylvestre reduced polyphagia, fatigue, blood glucose (fasting and post-prandial), and glycated hemoglobin and there was a favorable shift in lipid profiles and in other clinic-biochemical tests.
Gupta (1983) Gupta and Variyar (1964), Khare et al (1983), Baskaran et al (1990), Murakami et al (1996) and Kinghorn et al (2001) reported that Gymnema saponins I- II and gymnemic acids I-IX present in G.sylvestre neutralize excess sugar in diabetics. The administration of Inula racemosa and G. sylvestre extracts in combination proved to be more effective than the individual extracts.
These effects were comparable to a standard corticosteroid-inhibiting drug, ketoconazole. Daisy et al. (2009) reported that the dihydroxy gymnemic triacetate, the compound from G. sylvestre, possessed hypoglycemic and hypolipidemic activity in long-term treatment. Ahmed et al. (2010) found the gymnemic acid of leaf and callus extracts were responsible for the significant increase in the regeneration of β-cells in treated rats, when compared with the standard diabetic rats. All these studies confirm that G.sylvestre could be used as a drug for treating diabetes.
According to the authors, these extracts may not prove to be effective in thyroid hormone mediated type II diabetes but for corticosteroid induced diabetes mellitus. According to Al-Romaiyan (2010; 2012) G.sylvestre stimulates insulin secretion from mouse and human islets in vitro, at least in part as a consequence of Ca (2+) influx and protein kinase activation. Feeding G. sylvestre extract to the diabetic rats decreased the activity of glutathione peroxidase in cytosolic liver and glutamate pyruvate transaminase in serum to normal levels.
10. Aloe Vera:
Aloe Vera gel, the leaf pulp or mucilage, aloe latex, commonly referred to as aloe juice is a bitter yellow exudate from the pericyclic tubules just beneath the outer skin of the leaves. Extracts of aloe gum effectively increases glucose tolerance in both normal and diabetic rats. Single as well as chronic doses of bitter principle of the same plant also showed hypoglycaemic effect in diabetic rats.
This action of Aloe vera and its bitter principle is through stimulation of synthesis and/or release of insulin from pancreatic beta cells. Noel et al. (1997) have also reported aloe vera to be hypoglycaemic. Oral administration of ethanolic extract of Aloe vera at a concentration of 300 mg/kg.
(-1) body weight for 21 days resulted in a significant reduction in fasting blood glucose, thiobarbituric acid reactive substances, hydro-peroxides and alpha-tocopherol and significant improvement in ascorbic acid, reduced glutathione and insulin in the plasma of diabetic rats. Interestingly, the ethanolic extract of Aloe vera appeared to be more effective than glibenclamide in controlling oxidative stress.
Treatment with the extract also resulted in a significant increase in reduced glutathione, superoxide dismutase, catalase, glutathione peroxidase and glutathione- S-transferase in the liver and kidney of diabetic rats. These results clearly showed the anti-oxidant property of Aloe vera gel extract. The increased levels of lipid peroxidation and hydro-peroxides in tissues of diabetic rats were reverted back to near normal levels after the treatment with gel extract.
Oral administration of Aloe Vera gel extract at a dose of 300 mg/kg body weight per day to STZ-induced diabetic rats for a period of 21 days resulted in a significant reduction in fasting blood glucose, hepatic transaminases (aspartate aminotransferase and alanine aminotransferase), plasma and tissue (liver and kidney) cholesterol, triglycerides, free fatty acids and phospholipids and a significant improvement in plasma insulin.
The decreased plasma levels of high-density lipoprotein-cholesterol and increased plasma levels of low-density lipoprotein-cholesterol and very low- density lipoprotein-cholesterol in diabetic rats were restored to near normal levels following treatment with the extract. The altered fatty acid composition in the liver and kidney of diabetic rats was also restored following treatment with the extract.
11. Colocasia (Colocasia Esculenta):
Colocasia commonly known as ‘Alu and dasheen’ is widely used in traditional system of medicine for the treatment of diabetes mellitus. Kumawat et al. (2010) reported that 400 mg/kg of ethanolic extract of colocasia leaves showed anti-hyper-glycaemic activity in alloxan induced diabetic rats.
12. Soya (Glycine Max):
Cederroth et al. (2008) reported that mice fed with soy-rich diet have improved adipose and glucose metabolism. According to yhem, activation of the AMPK pathway by dietary soy is likely involved and may mediate the beneficial effects of dietary soy in peripheral tissues. Hence they suggested that dietary soy could prove useful to prevent obesity and associated disorders.
McCue et al. (2005) reported that sprouting and dietary fungal bioprocessing of soybean improved the anti-diabetic potential of soybean extracts, potentially through modulation of the phenolic profile of the extract, and further suggested that enzyme inhibitory activity may be linked to phenolic anti-oxidant mobilization during spouting and/or bio-processing.
13. Cranberry (Vaccinium Oxycoccos/Oxycoccus Palustris):
The enhanced functionality in terms of high alpha-glucosidase and alpha- amylase inhibitory activities of Cranberry indicated the potential for diabetes management, and the high ACE-I inhibitory activity indicated its potential for hypertension management.
14. Tulasi/Holy Basil (Ocimum Sanctum):
Since ancient times, Tulasi is known for its medicinal properties. The aqueous extract of leaves of Ocimum sanctum showed the significant reduction in blood sugar level in both normal and alloxan induced diabetic rats. Significant reduction in fasting blood glucose, uronic acid, total amino acid, total cholesterol, triglyceride and total lipid indicated the hypoglycaemic and hypo-lipidemic effects of tulsi in diabetic rats.
Oral administration of plant extract (200 mg/ kg) for 30 days led to decrease in the plasma glucose level by approximately 9.06 and 26.4 per cent on 15 and 30 days of the experiment respectively. Renal glycogen content increased 10 fold while skeletal muscle and hepatic glycogen levels decreased by 68 and 75 per cent respectively in diabetic rats as compared to control.
15. Neem (Azadirachta Indica):
Siddiqui (1942) found the active principle in neem to be the bitter principles nimbin, nimbinin, nimbidin. Siddiqui (1942), Murthy et al. (1978), Pillai and Santhakumari (1981) have all reported that neem leaf juice, bark and flowers to lower the blood glucose in diabetics. Hydroalcoholic extracts of this plant was found to show anti-hyperglycemic activity in streptozotocin treated rats and this effect is because of increase in glucose uptake and glycogen deposition in isolated rat hemi diaphragm.