Methylcellulose is part of the group "complex carbohydrates" and can absorb large quantities of water. Methylcellulose, and other cellulose derivatives are used in the manufacture of low calorie foods such as imitation syrups and salad dressings low in calories. Methylcellulose is a semisynthetic, bulk Forming Fiber Laxative used for short-term treatment of constipation.

Bulk laxatives absorb liquid in the intestines and swell to form a soft bulky stool. The bulky mass stimulates the intestinal muscles, speeding stool transit time through the colon. Methylcellulose will not work as a bulk forming laxative without increased fluid intake. Results usually occur within twelve to seventy two hours.

Fiber is found in the stems, seeds and leaves of plants. It is made up of chains of sugar but humans do not have the enzymes in their digestive tract to be able to break these chains down. A small amount of the fiber can be broken down by the enzymes of the bacteria that live in the human digestive tract. Most of the fiber is not broken down and goes out of the body in the feces. “Fiber” is a very broad term. More precise terms are soluble and insoluble fiber. Soluble fiber dissolves in water and can be broken down by bacterial enzymes, while insoluble fiber cannot. The distinction is important because the solubility of the fiber determines its health benefit. Fiber found in food is usually a mixture of both types of fiber, while purified fiber supplements may contain just one type of fiber.

Dietary sources of fiber are plentiful. Fruits, vegetables, seeds and legumes (dried peas and beans such as lentils, split peas, red beans and pinto beans) contain both types of fiber. Barley, oats, oat bran and rye contain predominantly soluble fiber. Wheat bran, brown rice and whole grains (grains that have not been refined) are excellent sources of insoluble fiber.

Supplemental sources of fiber include psyllium, methylcellulose or polycarbophil as well as fiber extracted from fruits, vegetables and grains. Psyllium is a concentrated source of fiber from the husks of the psyllium plant. Methylcellulose and polycarbophil are chemically altered forms of cellulose (the cell wall of many plants). The chemical alterations make them resistant to bacterial breakdown.

General health recommendations call for a daily consumption of 20-40 grams of fiber, but the average American consumes less than 15 grams. Although the amount of soluble and insoluble fiber is not specified, it is assumed that people will receive both types of fiber.