NOPAL (Opuntia streptacantha)
Nopal is a member of the cactus family and is also known as prickly pear. There are multiple species known as Opuntia, including O. megacantha, O. ficus indica, and O. streptacantha Lemaire. Research has focused on O. streptacantha Lemaire for its role in lowering blood glucose. Nopal has been used as a food in Mexico and the Southwestern part of the U.S. The leaves, flowers, stems, or fruit are used. Broiled stems or extracts of nopal have been used medicinally to lower blood glucose.19,75 Some individuals have prepared blended shakes mixed with fruit.
Nopal has been used to treat diabetes and high cholesterol.19,75 One extract has been used to reduce symptoms of hangover.102 Male patients have also used nopal to reduce symptoms of bladder fullness or urgency (benign prostatic hyperplasia, or BPH).103
Chemical Constituents and Mechanism of Action
Nopal contains mucopolysaccharide soluble fibers and phytochemicals, including pectin,75 which may slow carbohydrate absorption and decrease lipid absorption in the digestive tract. The benefit of nopal does not seem to depend on insulin presence, since it has demonstrated hypoglycemic activity in pancreatectomized animals.104 An additional theorized mechanism of action is increased insulin sensitivity, since insulin concentrations decrease with nopal administration.105
Adverse Effects and Drug Interactions
The major side effects of nopal include mild diarrhea, nausea, abdominal fullness, and increased stool volume.19,75 A case report of nopal and chlorpropamide coadministration resulted in additive effects on blood glucose and insulin levels, although hypoglycemia was not reported.106
Clinical Studies
Trials studying nopal are small and have mostly been published in Spanish, although abstracts are available in English. One trial was done in three groups of type 2 diabetes patients treated with diet alone or in combination with sulfonylureas.107 Oral medications were discontinued 72 hours before nopal was administered. After a 12-hour fast, one group of 16 patients received 500 g broiled nopal, a second group of 10 received 400 ml water, and a third group of 6 received 500 g broiled zucchini. Subjects had blood drawn at 60, 120, and 180 minutes after receiving the nopal, water, or zucchini. The nopal group had a significant decline from 222 mg/dl (12.3 mmol/l) fasting to 203 mg/dl (11.3 mmol/l), 198 mg/dl (11.0 mmol/l), and 183 mg/dl (10.2 mmol/l), respectively, at 60, 120, and 180 minutes after receiving the treatment (P < 0.001 compared with baseline).107
Another trial compared the effects of nopal in 14 patients on sulfonylureas to the effects in individuals without diabetes. Individuals in both groups received 500 g broiled nopal or 400 ml water. In the diabetes group, glucose declined by 21 mg/dl (1.2 mmol/l), 28 mg/dl (1.6 mmol/l), and 41 mg/dl (2.3 mmol/l) at 60, 120, and 180 minutes after nopal was administered (P < 0.005 for 60 and 120 minutes vs. baseline; P < 0.001 for 180 minutes vs. baseline).108 Insulin concentrations also declined significantly.
Summary
Nopal may help lower blood glucose when eaten cooked or taken as a dietary supplement. Although some individuals may prepare a blended shake using raw nopal, the raw stems may not lower blood glucose as effectively as when cooked. Nopal contains fiber and pectin, which may decrease carbohydrate absorption. The major side effects are diarrhea and increased stool volume. There are no long-term studies evaluating nopal for diabetes treatment. It is a benign agent and has been frequently consumed as a food. A frequently quoted dose is 100–500 g daily of broiled stems.19 An extract containing 1,500 IU taken prior to drinking large quantities of alcohol decreased hangover symptoms.102 For BPH, the dose used was 500 mg of powdered nopal flowers three times a day.103 Optimal doses of extracts have not been established to treat diabetes; therefore caution should be exercised regarding recommendation of nopal supplements. As a food, however, it appears quite safe.
ALOE (Aloe Vera L.)
Aloe is a member of the Liliaceae family. Derived from the Arabic alloeh, the name means “bitter and shiny substance.” Aloe grows well in Africa, the Mediterranean, the Caribbean, and warm areas of North and South America. Pictorial wall carvings of aloe have been found in Egyptian temples, and the Egyptian Book of Remedies (circa 1500 B.C.) notes the use of aloe to treat the skin and prepare drugs used as laxatives.75 Dried aloe leaf juice has been used as a laxative, whereas topical aloe gels have been used to treat wounds, psoriasis, sebhorrhea, sunburn, and dry skin. Orally, aloe has also been used to enhance the immune system and treat diabetes and hyperlipidemia.75 Aloe is highly used by Hispanic patients and may be called sábila.
Chemical Constituents and Mechanism of Action
Two forms of aloe are dried leaf juice and aloe gel.75 Latex from the pericyclic cells obtained beneath the skin of leaves may be evaporated to form a sticky substance known as “drug aloes” or “aloe.” This aloe juice contains cathartics including anthraquinone, barbaloin, a glucoside of aloe-emodin, and other substances. Aloe gel, however, is the ingredient relevant to diabetes. It comes from the inner portion of leaves and does not contain cathartics, but it does contain the polysaccharide glucomannan, which is similar to guar gum.75 Active ingredients include polysaccharides and glycoprotein, but although the definitive mechanism of action is unknown, the high fiber content alone may promote glucose uptake.109
Adverse Effects and Drug Interactions
No adverse effects have been reported with aloe gel. One study evaluated renal and hepatic function, and there were no adverse effects.110 Aloe did not cause blood glucose to be excessively lowered when combined with the sulfonylurea glibenclamide (glyburide).110 Nevertheless, caution should be exercised by patients combining aloe with secretagogues. An unusual adverse effect was reported in a case of an individual taking aloe who experienced excessive intraoperative blood loss during surgery where sevoflurane was used. This may be due to the fact that both sevoflurane and aloe inhibit thromboxane A2, which may decrease platelet aggregation and prolong bleeding time.111 There is also concern that inadvertent inclusion of aloe juice would produce a laxative effect and result in fluid or electrolyte disturbances.
Clinical Studies
In one very small uncontrolled study, five patients with type 2 diabetes were administered one-half teaspoonful dried aloe sap twice daily for 4–14 weeks.112 Information regarding blinding was not provided. Fasting glucose decreased from a mean 273 mg/dl (15.2 mmol/l) to 151 mg/dl (8.4 mmol/l; P < 0.001). Mean A1C also decreased from 10.6% to 8.2% (P value not reported).
A 6-week single-blind, placebo-controlled study was done in 40 patients with newly diagnosed type 2 diabetes.109 Aloe vera juice was pre pared from aloe gel. The patients received 1 tablespoonful aloe gel twice daily or placebo for 6 weeks. Fasting blood measurements were taken weekly, and triglyceride and