The tubers have traditionally been pounded to yield a powder for making noodles or gelatin for adding to stews, sauces, and soups. The tuber renders these foods richer, thicker, and more satisfying in much the same way that white flour or corn starch improves the texture of similar foods in the United States. But the Japanese have a better thing going than we do with our white starches. Ours tend to constipate, and are full of "empty" calories that contribute to weight gain and obesity. In comparison, konjac, or konnyaku, as it's called today, contains beta carotene, thiamin, and a number of minerals, including magnesium and manganese. It also contains chromium, a mineral with potential benefits in controlling sugar cravings and treating diabetes. But these are not the most impressive of konjac's ingredients: Glucomannan raises this tuber to near-angelic status.

Despite its evil-sounding nicknames, konjac has long been believed by the Japanese to move toxins out of the digestive tract. Studies show that they are probably right, and that konjac may help to prevent many diseases, including cancer, diabetes, gallstones, obesity, and heart disease. These studies provide support for food manufacturers who propose replacing white flour with konjac powder, not just to clean the intestines, but to serve as a weight-loss ingredient in many common foods.

Glucomannan is already available as a dietary supplement. Asian women have claimed for years that it helps them maintain a desired weight, and more and more Americans are determined to find out if it's true. Glucomannan is a polysaccharide, which means that chemically it is made up of simple sugars—specifically, mannose and glucose. It is also a soluble fiber and can absorb up to 200 times its weight in water.

Glucomannan reduces blood fats, discourages weight gain, helps to keep blood sugar levels normal, and relieves constipation. When ingested, it takes on a jelly-like consistency and expands to make the stomach feel full. People are therefore sated more quickly and are less likely to overeat, according to results of trials in which obese patients were put on calorie-restricted diets and glucomannan. In addition, like most food fiber, glucomannan acts as a bulking agent in the colon, which stimulates peristalsis (the muscular movement that causes bowel evacuation).

Clinical studies confirm that glucomannan in konjac tubers lowers cholesterol—both total cholesterol and low-density lipoprotein (LDL) cholesterol—without affecting diastolic blood pressure.

When given to obese children, konjac glucomannan (KG) decreased  cholesterol and triglyceride levels significantly, without any negative effects. Obese adults who took 1 gram KG with 8 ounces of water one hour before meals three times a day for eight weeks reported an average weight loss of 5.5 pounds, and overall reductions in total cholesterol and LDL cholesterol levels.

In one double-blind trial, ten days of treatment with KG returned the bowel habits of patients with chronic constipation to normal. Another study showed that patients given either 3 or 4 grams daily noted an average increase of three and six more bowel movements per week, respectively, without additional diarrhea or flatulence.

Konjac glucomannan helped to keep glucose at optimal levels in baboon blood, suggesting that KG may help control glucose levels in diabetics. A recent study indicates that this is likely to be true: When used along with conventional treatment, KG not only helped normalize and maintain blood sugar levels in patients with type 2 diabetes, it also lowered both cholesterol and systolic blood pressure.

Experimental studies also indicate that KG may protect against certain types of cancer. For those of us over the age of 60, this is welcome news. When elderly people are given glucomannan, the bacteria in the gut changes and encourages the growth of the so-called "good bacteria" such as Bifidobacterium. Increases in good bacteria are associated with a reduction in pro-cancerous nitrosamines, proteins thought to be responsible for the development of liver cancer and other cancers. Good bacteria also encourage better gut motility—motion, including peristalsis that leads to a bowel movement — thereby helping to move waste products out of the body before they can promote cancer or other illnesses.

Studies on diabetic rats indicate that long-term supplementation with konjac glucomannan may help prevent heart attacks and strokes in people who have diabetes. In diabetic rats put on diets high in cholesterol, glucomannan prevented the formation of aortal plaques, deposits that increase heart disease risk. Glucomannan may do this in humans, too, by reducing LDL cholesterol and blood sugar levels.

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