Konjac, also known as glucomannan, is an herb that grows in parts of Asia. It’s known for its starchy corm, a tuber-like part of the stem that grows underground. The corm is used to make a rich source of soluble dietary fiber.
Konjac is used as a gelatin substitute and to thicken or add texture to foods. It’s also used in traditional Chinese medicine. In the Western world, konjac is best known as a dietary supplement for weight loss and cholesterol management.
Glucomannan is generally well-tolerated. Like most high-fiber products, however, it may cause digestive problems such as:
- diarrhea or loose stools
- abdominal pain
The high fiber content of konjac has many health benefits. Soluble fiber helps lower cholesterol and blood glucose levels. A diet high in fiber may also help regulate bowel movements, prevent hemorrhoids, and help prevent diverticular disease. Here’s what the research says:
Konjac and constipation
A 2008 study found that glucomannan may help prevent constipation. The study showed that adding glucomannan to a low-fiber diet increased the amounts of probiotic bacteria in feces. It also increased bowel movement function by 30 percent.
Konjac and weight loss
Fiber is filling. Eating it regularly helps keep you fuller longer, so you’re less likely to overeat or snack between meals. Konjac also expands in the stomach to help keep you full.
According to a 2005 study, adding a glucomannan fiber supplement to a balanced, 1,200-calorie diet caused more weight loss than a 1,200-calorie diet plus a placebo. Adding an additional fiber supplement (guar gum or alginate) didn’t have an impact.
Konjac and cholesterol
A 2008 systematic review found that konjac may help lower total cholesterol, LDL (bad) cholesterol, and triglycerides. Konjac also reduced body weight and fasting blood sugar. Researchers concluded that glucomannan could be an adjuvant therapy for people with diabetes and high cholesterol. A later study found that konjac lowered LDL and recommended its use to reduce the risk of cardiovascular disease.
Konjac and skin health
Konjac supplements are available online or in most natural health stores. Supplements aren’t regulated by the Food and Drug Administration (FDA). Only buy them from reputable manufacturers.
Take konjac with plenty of water, preferably before a meal. There’s no approved, standardized dose of konjac. Recommended dosages vary by manufacturer and what you’re using it for. They typically range from 2 to 6 grams. Follow the manufacturer’s dosage instructions, or contact your doctor or a qualified natural health practitioner for advice.
According to the FDA, some konjac candies have caused choking deaths in the elderly and in children. This prompted the FDA to issue an import alert in 2011 for konjac candies. Konjac candies have a gelatinous structure that doesn’t dissolve in the mouth like other gelatin products.
Konjac supplements may also expand in your esophagus or bowel and cause an obstruction. The risk is higher if you:
- take konjac tablets
- take konjac in any form without water
- are elderly
- have problems swallowing
Several countries have banned the use of konjac because of the high incidence of bowel or throat obstruction. Children and pregnant or breastfeeding women should not take konjac supplements.
Stop taking konjac and get medical help if you have symptoms of an allergic reaction such as:
- difficulty breathing
- hives or a rash
- itchy skin
- rapid heart rate
Konjac has been shown to lower blood sugar levels. It may slow the absorption of sugar, so people with diabetes should closely monitor their blood sugar. Consult your doctor before using konjac if you take insulin or other diabetes medications.
Konjac is a plant that’s been used for centuries in Asia as food and medicine. Research has shown it may help you fight constipation and reduce cholesterol. More studies are needed, but konjac may also support weight loss. The best formula for reducing the number on the scale is still a healthy diet and regular exercise.