Fiber adds bulk to your meals but very few calories. When you eat foods high in fiber, you can eat the same amount of food but feel more satisfied than you would after eating foods that are low in fiber. One type of fiber, called soluble fiber, turns into a gel-like substance when it comes in contact with stomach juices. This sludge helps slow down your digestion and can help you feel fuller for longer after eating. Metamucil and some other fiber supplements are made from psyllium husks, derived from the small, gel-like seeds of the Plantago ovata plant. Psyllium is up to 70 percent soluble fiber.