What is konjac? Uses, benefits, and side effects

Sifting through shelves loaded with dietary supplements or alternative grocery store products that make a range of claims can be daunting. But the idea that noodles might be good for your diet is a revolutionary one worth a second look. 

Konjac noodles have gotten a more prominent place on the shelf lately. These noodles are made from the konjac plant which has a starchy root packed with dietary fiber. Used in traditional Asian medicine and cooking for centuries, researchers have been exploring whether the konjac root and the glucomannan fiber it contains may be of some benefit when it comes to managing things like diabetes, constipation, and obesity. Let’s look at precisely what konjac is and what type of health benefits it offers. 

Known scientifically as Amorphophallus konjac, konjac is a tuberous plant that’s sort of like a yam. You may also hear it called elephant foot yam due to the unique appearance of the tubers it produces. 

Konjac glucomannan (just konjac or glucomannan for short) is the dietary fiber extracted from the plant’s root. Glucomannan has been used in traditional Chinese medicine for over 2,000 years to treat asthma, blood diseases, skin conditions, and more (Chua, 2010). Let’s take a look at some other popular uses of this herbal remedy.

Weight loss

Food and many supplements that contain glucomannan claim the fiber helps with weight loss. In general, there are two main types of fiber that are good for your gut. One is insoluble dietary fibers, which serves as a food source for the bacteria that live there. When your good gut bacteria are happy, your gut is happy. 

The other type is called viscous dietary fiber. Glucomannan falls into this category. Viscous dietary fibers keep you feeling full for longer by absorbing liquid and bulking up in your digestive tract. It forms a gel that stays in your stomach for a longer time, which is why you feel full for longer.

Research finds that glucomannan is an effective tool for helping people with obesity lose weight when combined with a healthy, low-calorie diet (Bjerketvedt, 2005). A review of six studies demonstrated that taking glucomannan supplements helped significantly reduce weight in people who were overweight or have obesity (Mohammadpour, 2020).

Blood sugar control

Type 2 diabetes, a condition characterized by high levels of sugar (or glucose) in the blood, is prevalent in the United States. One function of fiber is to help those sugar levels by slowing our body’s absorption of sugar from your diet. Fiber also can improve your body’s response to the sugar-regulating hormone insulin. 

People with type 2 diabetes often benefit from weight loss. When you have excess weight on your body, the tissues that respond to insulin become less sensitive to it. This is referred to as insulin resistance. Glucomannan may help people with diabetes lose weight and decrease their insulin resistance. 

Konjac also decreases the amount of sugar absorbed by the intestines. This is important for keeping blood sugar low and maintaining healthy insulin levels. As a result, konjac can make your body even more responsive to insulin you make (Shah, 2015). 

One study compared the effects of glucomannan supplements on healthy blood sugar, high blood sugar, and borderline blood sugar (an indicator of prediabetes). Prediabetes is a condition in which your blood sugar is higher than it should be, but not high enough to be considered diabetes. Even in people with borderline high results, glucomannan helped regulate and control blood sugar levels (Yoshida, 2020).

Cholesterol

Despite the bad rap it gets, not all cholesterol is bad. Some types, like HDL (high-density lipoprotein), are considered “good” cholesterol. Others, like LDL and triglycerides––not so much. High levels of LDL or “bad” cholesterol is linked to higher risk for heart disease and stroke. 

Dietary fiber has been found to help lower cholesterol levels. One study found that konjac glucomannan significantly lowered LDL levels in both adults and children (Ho, 2017).

Constipation

Eating enough dietary fiber is linked to better bowel health. It makes stool softer and easier to pass. In some studies, Konjac glucomannan supplements contributed to this effect.  

One clinical trial found that konjac glucomannan supplements made stools softer and happen more frequently. It also had beneficial prebiotic effects, meaning it supports the growth of “good” bacteria in the gut (Chen, 2006). 

Some studies had different results, though. One small study in children with constipation found that overall, konjac slightly increased the frequency of bowel movements but not dramatically enough to consider it a good treatment option (Han, 2017).

Konjac supplements come as capsules, tablets, and powder you can add to food, drinks, or sauces. Most studies cite a typical dose as 2–4 grams per day, but since it’s not regulated by the FDA, there are no official dosing guidelines. 

Konjac root powder and flour are sometimes used to make food products. An example you may be familiar with is konjac or shirataki noodles. Some people opt for these noodles instead of wheat-based ones to reduce their caloric intake and feel full longer. However, there are some reports that the noodles (like the supplement) can cause mild digestive upset (Zhang, 2014).

Most side effects of glucomannan are mild and affect the digestive system. Common ones include bloating, diarrhea, gas, upset stomach, and burping (Wharton, 2019). 

It’s rare, but there have been occasional reports of more severe reactions. For example, supplements can expand inside your digestive tract and cause a blockage. There was a case in Australia where a woman had a severe blockage in her intestines after eating konjac flour noodles (Jackman, 2018). 

It can also get stuck in your throat and become a choking hazard. There has been a case of a throat blockage in one woman who was taking a glucomannan supplement (Vanderbeek, 2007). Several gel candies containing konjac have been identified as choking hazards and are banned by the U.S. Food and Drug Administration (FDA) (FDA, 2002). 

Dietary fiber is an important part of bowel health and science shows it’s beneficial for people with diabetes, obesity, and high cholesterol, as well as people looking to treat constipation. Speak with a healthcare provider about ways to incorporate konjac into your routine.

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Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

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Current version

February 10, 2022

Written by

Gina Allegretti, MD

Fact checked by

Yael Cooperman, MD

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About the medical reviewer

Yael Cooperman, MD, Ro

Yael Cooperman is a physician and works as a Senior Manager, Medical Content & Education at Ro.