What it is: Edible fiber from the root of the Asian konjac plant, available in capsules, powder form, and shirataki noodles (traditional Japanese noodles similar to udon in texture). It’s a condensed form of fiber, swelling up to 17 times its volume in water.
How it works: More than any other type of fiber, it may help you drop pounds by making you feel satisfied after eating and by allowing food to be eliminated before it has a chance to be absorbed, says registered dietitian David Grotto, the author of The Best Things You Can Eat ($16, amazon.com).
Good to know: You may prefer the pills to the noodles, which can be gummy. You’ll need about one to five grams a day, and the fiber may be most powerful when combined with exercise: Overweight women who took glucomannan and exercised for an hour three times a week lost 50 percent more fat than did women who supplemented with glucomannan but didn’t exercise, according to a 2007 study from the journal Metabolism.