Konjac is a perennial plant of the genus Amorphophallus that grows in tropical and subtropical regions of eastern Asia, from Indonesia to India, Japan and China. It is known primarily for its starchy corm, a tuber-like structure that is actually part of the plants stem, but which grows underground and acts as a storage organ for the plant.
Konjac is also known as elephant yam, presumably for the resemblance of its corm to that of the true yam, but the plants are not closely related. Other colloquial names for Konjac are konjaku, devils tongue, snake palm and voodoo lily.
Konjac is primarily used as a source of glucomannan, a dietary fiber that makes up about 40% of the plants corm. Glucomannan is used as a food additive for its thickening and emulsifying properties, and as a nutritional supplement for the treatment of obesity, constipation, high cholesterol, diabetes and acne. It provides a rich source of soluble fiber, considered to be of general benefit to the digestive system, while containing almost no calories.
Where it Come From
Konjac is cultivated in China, India, Japan and Korea. In nature, the plant grows best in tropical or subtropical conditions that provide moderate rainfall and a soil structure that combines a somewhat sandy top layer with a lower layer of mud that can retain water. In Japan and China, it is often cultivated in hilly terrain that is not conducive to traditional agriculture, and each plant requires very little room to get started.
Plants are typically transplanted and more widely spaced in their second and third years, at which time they reach maximum levels of glucomannan content. They are then dug out of the ground for cleaning and processing.
Traditional processing after the harvest is a very labor intensive operation. The corms are separated from the rest of the plant and washed and peeled by hand before being sliced and dried in the sun. Modern processing incorporates machinery and accelerates the drying process with air heated by burning coal. Regardless of the process used, the goal is to produce a product that is dry enough to be stored and to achieve greater concentrations of glucomannan.
The extent to which konjac is processed depends on whether its intended use is as a food, food additive or nutritional supplement.
Konjac flour is made by grinding the dry corms and separating the lighter components from the heavier flour. What is left contains approximately 70% glucomannan, and is suitable for use in noodles and other dishes. The flour can be further processed to achieve 80% glucomannan content, yielding konjac jelly or gum for use as a thickener or gelling agent, or purified as part of a final stage that produces the soluble fiber used as a nutritional supplement.
History and Origin
Konjac is regularly mentioned in historical Chinese treatises and histories, both as a medicine and, particularly in times of famine, as a food. The earliest known use of konjac as a medicinal herb dates back to the Han Dynasty in China, some two thousand years ago, where it was recommended as a treatment for asthma, infection, cough and skin disorders. Its use continued through subsequent dynasties and has been essentially uninterrupted through the present day.
Konjac, in both flour and jelly form, has a long culinary history in China and Japan. In Chinas Sichuan province, the jelly is used as a tofu substitute and called konjac tofu.In Japan, where it is called konyaku konjac flour is mixed with water and limewater and boiled. Once it solidifies, it can be cut into various shapes. Cut into thin wafers, it can take the place of tofu or thinly sliced raw fish. It is perhaps best known, however, when cut into strips and takes the place of noodles in several stew-like dishes, where it is appreciated for its unique texture. Konjac itself has little or no taste.
Western interest in konjac and glucomannan has grown over the past two decades as the health benefits of dietary fiber have become better understood. Research has focused on its potential for controlling cholesterol and blood glucose, as an aid to losing weight and as a general benefit to digestive health. Results of those studies have been promising. The broader therapeutic claims of traditional Chinese medicine have not been subjected to the same scrutiny and remain unproven.
Uses and Benefits of Konjac
Today, konjac is used for two distinct but related purposes: losing weight and supplementing dietary fiber. Both uses find support in the medical literature, but konjac has also been the subject of unproven claims that have resulted in government intervention.
The efficacy of konjac for weight loss relies on its ability to absorb up to twenty times its own weight in water. The glucomannan expands after ingestion, and this tends to promote a feeling of fullness as it travels through the digestive tract. To achieve this result, konjac is generally taken with water before meals. An alternative, if less popular, approach is to sprinkle granules of glucomannan directly on food.
Recommended doses for weight loss purposes range from one to four grams of glucomannan taken with eight ounces of water one hour before each meal.
The American Dietary Association recommends that adults should consume at least 20 to 35 grams of fiber each day. The typical American diet provides between 12 and 18 grams. While oat bran, at 14% soluble fiber content, offers the most concentrated sources of soluble fiber among those catalogued by the ADA, glucomannan comprises at least 40% of konjac by dry weight, making konjac the richest source of soluble fiber in nature.
Clinical studies specific to glucomannan supplementation have shown positive results in the treatment of a number of conditions, including:
Soluble fiber absorbs water, softens digestive contents and increases stool volume.
Hyperglycemia and Hypoglycemia
Glucomannan attracts water in the digestive system and becomes a gel, slowing digestive processes and trapping carbohydrates so that blood sugar levels are stabilized.
One benefit of the ability to regulate blood sugar levels is seen in Type 2 Diabetes, where glucomannan has shown potential to reduce blood glucose, insulin and serum lipid levels after meals, an effect that seems to be enhanced by glucomannans relatively high viscosity compared to other soluble fibers.
By attaching itself to bile acids in the digestive system and moving them out of the body, glucomannan supplements can help lower cholesterol and reduce the amount of fat present in the blood.
High Blood Pressure
As a corollary to glucomannans beneficial effect on cholesterol levels, one study has demonstrated a decrease in systolic blood pressure in healthy men after a four week course of glucomannan supplements.
While all of the above benefits are supported by medical research on human test subjects, the clinical studies themselves have uniformly involved relatively small groups of people and short periods of time. It is unclear, then, if the beneficial effects of konjac supplements can be counted on to persist over the long term.
In addition, some studies, even those not looking specifically at glucomannan as a weight loss product, have limited their subjects to people who are obese, making it unclear if konjacs benefits extend to people who are not overweight.
However, soluble fiber in general has been studied extensively, with a great deal of attention to the fact that it produces short-chain fatty acids as it is digested. These acids, in turn, provide a number of health benefits, including:
- Decreasing synthesis of cholesterol by the liver
- Regulation of insulin release by the pancreas
- Regulation of glucose absorption by affecting glucose transporters in the intestinal mucosa
- Discouraging the formation of polyps by raising the acidity level of the colon
- Enhancing the absorption of minerals, especially calcium, in the digestive system
- Increasing the production of a variety of cells and antibodies involved in the immune system
- Decreasing the ability of irritants to adhere to the mucosal layer of the colon
Konjac has itself been claimed to be something of an antidote to food poisoning. This claim originates from a single laboratory study in which 18 different food products were subjected to exposure to bacteria, including E. Coli and Salmonella, which were allowed to bind themselves to the products.
When the levels of bound bacteria were measured, the largest quantity were bound by sesame seed extract and konjac gum, leading to the tentative conclusion that konjac may help to prevent bacteria from entering host cells. This claim awaits further confirmation, as the effect has not been studied in a clinical setting to date.
A number of companies have been sanctioned for making false or misleading claims about the benefits of konjac and glucomannan. The sanctions have generally resulted from the companies exaggeration of the benefits conferred by konjac, from false claims of research support for those exaggerated benefits and from the use of expert endorsers whose expertise and qualifications are similarly exaggerated.
A typical example involves two products called FiberThin and Propolene, which were advertised via infomercials that claimed they would cause rapid and substantial weight loss without any need to exercise and regardless of what the consumer ate. The Federal Trade Commission required the companies involved to pay $1.5 million in settlement of the claims. They were also barred from making unsubstantiated claims for dietary supplements and from misrepresenting scientific studies in their marketing.
A different unproven claim may have its origin in the recommendations found in ancient Chinese herbal texts that list konjac as a treatment for acne and other skin conditions. Today, konjac can be found in several cosmetics and beauty treatments, which typically characterize it as a component that increases the effectiveness of other ingredients. There does not appear to be any research, pro or con, involving these claims.
Side Effects and Cautions
Konjac is not known to have undesirable side effects when used in food preparation or when taken as directed as a nutritional supplement, and its negligible calorie content make it particularly suitable as an aid to weight loss.
This is not to say that it is absolutely safe. Dangers associated with glucomannan stem from its ability to increase in volume by absorbing large quantities of water. These dangers have led to government intervention of two varieties:
Products containing glucomannan have been required to include information warning consumers of dangers if the product is not consumed as instructed. For example, Health Canada issued a warning in 2010 that glucomannan in tablet, capsule or powder form should always be taken with at least eight ounces of water and that it should be entirely avoided immediately before bed. Products containing glucomannan are required to carry those instructions and to note the risk of choking and/or blockage of the throat, esophagus or intestine if the product is taken without sufficient liquid.
In 2001, several deaths and near-deaths of children and the elderly from suffocation while eating a certain type of konjac fruit jelly candy were reported in California. Unlike jellies that melt on contact with saliva, konjac jellies require chewing and, if unchewed, can be inadvertently sucked into the throat. As the jelly expands, breathing can be cut off. The Food and Drug Administration banned sale of the candies in the United States in 2001, a ban followed soon thereafter by the European Union, Canada and Australia. The candies are still available in parts of Asia, but are sold with warning labels and manufactured in larger sizes and in formulations that dissolve more easily.
Dosage, Administration and Cost
As a nutritional supplement, konjac is available in tablet, capsule and powder form. Dosage consists of the equivalent of 500 to 1500 milligrams taken before meals with at plenty of water. If using the powder, it should be stirred briskly in water and it is important to drink the solution before it has a chance to gel.
Konjac can be readily found online or at retail drugstores and nutrition stores like GNC. It is most commonly sold in capsules containing approximately 700 milligrams of glucomannan. Prices are extremely variable, ranging from under $3.00 to almost $20.00 for 100 capsules. Konjac powder can be a cost-effective alternative, but with similar pricing variability. At the extremes, a 500 gram bag of powder can be purchased for $18.00, while buying 500 grams in 100 gram bottles can cost at least five times as much.
Konjac is also found in multi-ingredient supplements, where it is frequently combined with other fiber sources or with ingredients claimed to be effective in losing weight.
Konjac is also available as a food product, most often as noodles in a variety of shapes and sizes. Some brands have added flavoring, as konjac imparts little or no flavor on its own. Prepared noodles can be found online or at Asian grocery stores and are typically sold packed in water in plastic bags. They can be stored at room temperature and have a shelf life of approximately one year.
For the truly determined, konjac powder can be mixed with water and pickling lime in order to make konjac noodles from scratch. The mixture is boiled for three minutes and allowed to cool. Once cooled, it forms a stable, non-reversible gel which can then be cut into whatever shape is desired.