Konjac is a root vegetable 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 known as glucomannan.

People use konjac as traditional medicine and as a food source to make noodles and snacks.

In the Western world, it’s used as a food additive and dietary supplement to lower plasma cholesterol, improve carbohydrate metabolism, and help bowel movements.

Recently, you may find it in grocery stores as shirataki noodles.

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 (or “bad”) cholesterol, and triglycerides. Konjac also reduced body weight and fasting blood sugar.

Researchers concluded that glucomannan could be an adjuvant (additional) therapy for people with diabetes and high cholesterol.

A later study found that konjac lowered LDL cholesterol and recommended its use to reduce the risk of cardiovascular disease.

Konjac and skin health

According to a 2013 study, konjac can reduce acne and improve the health of your skin. It’s thought to reduce allergic response and improve wound healing.

You can use konjac as a noodle in stir fry dishes as well as in powder form in baked goods and sauces.

Konjac supplements are available online or in most natural health stores. The Food and Drug Administration (FDA) regulates dietary supplements under a different set of regulations than those covering “conventional” foods and drug products.

Under the Dietary Supplement Health and Education Act of 1994 (DSHEA), a firm is responsible for determining that the dietary supplements it manufactures or distributes are safe and that any claims made about them are supported by adequate evidence to show that they’re not false or misleading.

It’s best to only buy konjac supplements 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 the konjac for.

Make sure to follow the manufacturer’s dosage instructions, or contact your doctor or a qualified natural health practitioner for advice.

Glucomannan is generally well-tolerated. However, as with any high fiber product, it may cause digestive problems, such as:

  • bloating
  • diarrhea or loose stools
  • abdominal pain
  • gas
  • nausea

According to the FDA, some konjac candies have caused choking deaths in older adults and children. This prompted the FDA to issue an import alert for konjac candies.

Konjac candies have a gelatinous structure that doesn’t dissolve in your 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 older
  • 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 people 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
  • swelling

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 as traditional medicine. Research has shown that it may help you ease constipation and reduce cholesterol.

Konjac may also support weight loss, but more studies are needed. The best formula for losing weight is still a healthy diet and regular exercise.