苦瓜治糖尿，是真是假？

苦瓜: Bitter Melon
學名：Momordica charantia
英文：Balsam pear,Bitter Melon, Bitter gourd

首先介紹中醫對苦瓜的認識。
別名：涼瓜, “君子菜” (因苦瓜雖苦，卻從不會把苦味傳給“別人”，如用苦瓜燒魚，魚塊絕不沾苦味，所以有這雅稱。)
原產亞洲熱帶地區，廣泛分佈於熱帶、亞熱帶和溫帶 印度、日本以及東南亞地區栽培歷史久遠，中國栽培歷史約600年。
苦瓜氣味苦、無毒、性寒，入心、肝、脾、肺經；具有清熱祛暑、明目解毒、利尿涼血、解勞清心、益氣壯陽之功效；主治中暑、暑熱煩渴、暑癤、痱子過多、目赤腫痛、癰腫丹毒、燒燙傷、少尿等病症。我找不到傳統中醫用苦瓜治糖尿病的文獻。
注 意事項 :　苦瓜性涼，食苦味食品不宜過量，多食易傷脾胃，過量易引起噁心、嘔吐等，所以脾胃虛弱的人更要少吃苦瓜。苦瓜仁(籽) 味苦甘，卻可“益氣壯陽”。 此處壯陽，殆指腎火積熱，房事一觸即洩，得苦瓜仁散其邪熱，性事反得平衡而復正常，故能壯陽。 若體弱虛寒的陽痿，服之益增其痿矣。
一般傳言說苦瓜含奎寧Quinine，會刺激子宮收縮，引起流產，因此孕婦慎食。但研究顯示奎寧Quinine並沒有引起流產的功效，過量只能毒傷腎臟和引致死亡 。

苦瓜在印度一向是民間用來治療2型糖尿病的。在實驗研究用的2型糖尿白老鼠，已證實苦瓜能提高2型糖尿病鼠對胰島素的敏感，減低糖尿病的病狀（如口乾多飲水，多尿和尿中有糖份），並降低空腹血糖和胰島素的水平。即是說，苦瓜能治療有2型糖尿病的白老鼠。

苦瓜如何達到這效果呢？它可能有數個機制去降血糖，但其中一個現今較清楚的是，苦瓜有四種化學物，可能有類似胰島素作用的化學物，能刺激肌肉細胞和脂肪細胞表面的「胰島素接受體」，來提升細胞裏一個蛋白 AMP-Activated Kinase（AMPK），而這AMPK會使細胞造出更多的「葡萄糖轉運體4 」Glucose Transporter-4 (GLUT-4)，放置在細胞表面。顧名思義，這GLUT-4是負責讓血糖從血液中轉運（滲進）細胞，而當身體的肌肉和脂肪細胞都多些GLUT-4，則血液中糖份自然下降，從而改善了糖尿病。

那麼苦瓜對2型糖尿病病人的效果又如何呢？根據Cochrane Library的數據，在較大型的隨機、臨牀測試中，暫時苦瓜的作用與安慰劑無異，即未能證明療效，並提議需要更多觀察研究Observational Study。

對 各位2型糖尿病的患者，又希望苦瓜能幫助改善病況的，有何實用的建議呢？有，你可以多食苦瓜，天天吃也無大礙，實驗老鼠吃下大劑量的苦瓜也不見在肝腎的損 傷，正常的飲食量應該是安全的。若天天吃苦瓜，2型糖尿病會否改善？可能會，但苦瓜並不能取代你現時所吃的糖尿藥。若多食苦瓜後而經醫生檢查和抽血，發現 糖尿有改善，可能有減少用藥的空間。

不過，就算苦瓜被臨牀證實有改善2型糖尿病，也只不過是把過多的糖份從血液運到肌肉細胞中儲存，但這 「貨倉」也有飽和，甚至滿瀉的一日，到那刻糖尿又可能再惡化。而對付2型糖尿病，更重要的是戒口和做運動，因為做運動是提升AMPK和「葡萄糖轉運體4 」 GLUT-4的快捷方法，證實能改善糖尿病。而運動亦會燒耗了肌肉中的糖份，使它能源源不絕的去「吸」糖。做運動加上適當的戒口，才是治理2型糖尿病的「王道」，用藥和食療，假如有效，也只是輔助的方法而已。

"Antidiabetic Activities of Triterpenoids Isolated from Bitter Melon Associated with Activation of the AMPK Pathway". Chemistry & Biology 15 (3): 263–273.

Four cucurbitane glycosides, momordicosides Q, R, S, and T, and stereochemistry-established karaviloside XI, were isolated from the vegetable bitter melon (Momordica charantia). These compounds and their aglycones exhibited a number of biologic effects beneficial to diabetes and obesity. In both L6 myotubes and 3T3-L1 adipocytes, they stimulated GLUT4 translocation to the cell membrane—an essential step for inducible glucose entry into cells. This was associated with increased activity of AMP-activated protein kinase (AMPK), a key pathway mediating glucose uptake and fatty acid oxidation. Furthermore, momordicoside(s) enhanced fatty acid oxidation and glucose disposal during glucose tolerance tests in both insulin-sensitive and insulin-resistant mice. These findings indicate that cucurbitane triterpenoids, the characteristic constituents of M. charantia, may provide leads as a class of therapeutics for diabetes and obesity.

"Antihyperglycemic effects of three extracts from Momordica charantia" J Ethnopharmacol 88 (1): 107–11.

Momordica charantia (L.) (Cucurbitaceae) commonly known as bitter gourd or karela is a medicinal plant, used in Ayurveda for treating various diseases, one of which is diabetes mellitus. In this study, various extract powders of the fresh and dried whole fruits were prepared and their blood glucose lowering effect compared by administrating them orally to diabetic rats. The aqueous extract powder of fresh unripe whole fruits at a dose of 20 mg/kg body weight was found to reduce fasting blood glucose by 48%, an effect comparable to that of glibenclamide, a known synthetic drug. This extract was tested for nephrotoxicity, hepatotoxicity and biochemical parameters such as SGOT, SGPT and lipid profile. The extract did not show any signs of nephrotoxicity and hepatotoxicity as judged by histological and biochemical parameters. Thus the aqueous extract powder of Momordica charantia, an edible vegetable, appears to be a safe alternative to reducing blood glucose.


"Effect of bitter gourd (Momordica charantia) on glycaemic status in streptozotocin induced diabetic rats". Plant Foods Hum Nutr. 60 (3): 109–12.

Bitter gourd (Momordica charantia), a commonly consumed vegetable is used as an adjunct in the management of diabetes mellitus. A study was carried out to examine the effect of edible portion of bitter gourd at 10% level in the diet in streptozotocin induced diabetic rats. To evaluate the glycaemic control of bitter gourd during diabetes, diet intake, gain in body weight, water intake, urine sugar, urine volume, glomerular filtration rate and fasting blood glucose profiles were monitored. Water consumption, urine volume and urine sugar were significantly higher in diabetic controls compared to normal rats and bitter gourd feeding alleviated this rise during diabetes by about 30%. Renal hypertrophy was higher in diabetic controls and bitter gourd supplementation, partially, but effectively prevented it (38%) during diabetes. Increased glomerular filtration rate in diabetes was significantly reduced (27%) by bitter gourd. An amelioration of about 30% in fasting blood glucose was observed with bitter gourd feeding in diabetic rats. These results clearly provided experimental evidence that dried bitter gourd powder in the diet at 10% level improved diabetic status signifying its beneficial effect during diabetes.

"Bitter gourd (Momordica Charantia): A dietary approach to hyperglycemia". Nutr Rev. 64 (7 Pt 1): 331–7.

Bitter gourd (Momordica charantia) is a vegetable with pantropical distribution. It contains substances with antidiabetic properties such as charantin, vicine, and polypeptide-p, as well as other unspecific bioactive components such as antioxidants. Metabolic and hypoglycemic effects of bitter gourd extracts have been demonstrated in cell culture, animal, and human studies. The mechanism of action, whether it is via regulation of insulin release or altered glucose metabolism and its insulin-like effect, is still under debate. Adverse effects are also known. Nevertheless, bitter gourd has the potential to become a component of the diet or a dietary supplement for diabetic and prediabetic patients. Well-designed interdisciplinary research by nutritionists, medical doctors, and agronomists is needed before a dietary recommendation can be given and a product brought to the market.

"Hypoglycemic activity of the fruit of the Momordica charantia in type 2 diabetic mice". J Nutr Sci Vitaminol (Tokyo) 47 (5): 340–4.

The antidiabetic activity of Momordica charantia L. (Cucurbitaceae) was investigated in KK-Ay mice, an animal model with type 2 diabetes with hyperinsulinemia. The water extract of the fruit of Momordica charantia L. (MC) reduced the blood glucose of KK-Ay mice 3 weeks after oral administration (p<0.01) and also significantly lowered the serum insulin of KK-Ay mice under similar conditions (p<0.01). However, MC did not affect the blood glucose in normal mice. MC-treated KK-Ay mice blood glucose significantly decreased in an insulin tolerance test. Moreover, the muscle content of facilitative glucose transporter isoform 4 (GLUT4) protein content in the plasma membrane fraction from muscle significantly increased in the orally MC-treated mice when compared with that of the controls (p<0.01). These results suggest that the antidiabetic effect of MC is derived, at least in part, from a decrease in insulin resistance because of the increase of GLUT4 protein content in the plasma membrane of the muscle.


"Slow Acting Protein Extract from Fruit Pulp of Momordica charantia with Insulin Secretagogue and Insulinomimetic Activities." Biological & Pharmaceutical Bulletin
Vol. 29 (2006) , No. 6 1126

The protein from Thai bitter gourd (Momordica charantia) fruit pulp was extracted and studied for its hypoglycemic effect. Subcutaneous administration of the protein extract (5, 10 mg/kg) significantly and markedly decreased plasma glucose concentrations in both normal and streptozotocin-induced diabetic rats in a dose-dependent manner. The onset of the protein extract-induced antihyperglycemia/hypoglycemia was observed at 4 and 6 h in diabetic and normal rats, respectively. This protein extract also raised plasma insulin concentrations by 2 fold 4 h following subcutaneous administration. In perfused rat pancreas, the protein extract (10 μg/ml) increased insulin secretion, but not glucagon secretion. The increase in insulin secretion was apparent within 5 min of administration and was persistent during 30 min of administration. Furthermore, the protein extract enhanced glucose uptake into C2C12 myocytes and 3T3-L1 adipocytes. Time course experiments performed in rat adipocytes revealed that M. charantia protein extract significantly increased glucose uptake after 4 and 6 h of incubation. Thus, the M. charantia protein extract, a slow acting chemical, exerted both insulin secretagogue and insulinomimetic activities to lower blood glucose concentrations in vivo.

Cochrane Database Syst Rev. 2010 Feb 17;2:CD007845.
Momordica charantia for type 2 diabetes mellitus.

Abstract
BACKGROUND: Momordica charantia is not only a nutritious vegetable, but is also used in traditional medical practices­ to treat type 2 diabetes mellitus. Experimental studies with animals and humans suggested that the vegetable has a possible role in glycaemic control.
OBJECTIVES: To assess the effects of mormodica charantia for type 2 diabetes mellitus.
SEARCH STRATEGY: Several electronic databases were searched, among these The Cochrane Library (issue 4, 2009), MEDLINE, EMBASE, CINAHL, SIGLE and LILACS (all up to November 2009), combined with handsearches. No language restriction was used.
SELECTION CRITERIA: Randomized controlled trials that compared momordica charantia with a placebo or a control intervention with or without pharmacological or non-pharmacological interventions were included.
DATA COLLECTION AND ANALYSIS: Two authors independently extracted the data. Risk of bias of trials was evaluated using the parameters of randomization, allocation concealment, blinding, completeness of outcome data, selective reporting and other potential sources of bias. A meta-analysis was not performed given the quality of data and the variability of preparations of momordica charantia used in interventions (no similar preparation was tested twice).
MAIN RESULTS: Three randomised controlled trials with up to three months duration and investigating 350 participants met the inclusion criteria. Risk of bias of these trials (only one study was published as a full peer-reviewed publication) was generally high. Two RCTs compared the effect of preparations from different parts of the momordica charantia plants and placebo on the glycemic control in type 2 diabetes mellitus. There was no statistically significant difference compared to placebo. The effects of preparation from the leaves of the plant and glibenclamide were comparable in the third trial. No serious adverse effects were reported in all the trials. There were no documentations of death from any cause, morbidity, (health-related) quality of life and costs.
AUTHORS' CONCLUSIONS: There is insufficient evidence to recommend momordica charantia for type 2 diabetes mellitus. Further studies are therefore required to address the issues of standardization and the quality control of preparations. For medical nutritional therapy, further observational trials evaluating the effects of momordica charantia are needed before RCTs are established to guide any recommendations in clinical practice.
PMID: 20166099 [PubMed - indexed for MEDLINE]