How do fiber pills work?

[Sapo]

I understand that fiber works by being a large volume of indigestible stuff that moves along the GI tract and wipes it clean, as it were. But how does a small pill do that? I guess they puff up some with water, but even if it went from pill size to, say orange size (which is a lot of growing), that is still very little to replace having your greens. What am I missing?

[Gfactor]

Here is a sort of answer:

Consider oatmeal: A 3/4 cup serving of cooked oatmeal has almost 3 grams of fiber. A small salad with spinach, tomato, cucumber and broccoli also contains about 3 grams of fiber. Comparatively, three tablets of a popular fiber supplement will give you the same 3 grams. What’s the downside of the pills? Dietitians and nutritionists would point out that food has many other nutritional benefits besides the fiber content: vitamins, minerals, protein and other substances no one has evaluated yet. Plus food tastes better. The other issue is that pills are an expensive way to get fiber.

Weight Loss, Diets, Nutrition & Exercise at The Diet Channel

And there’s no evidence that the pills help much: American Dietetic Association Complete Food and Nutrition Guide - Duyff, ADA (American Dietetic Association) - Google Books

[Gfactor]

In other words, it’s the fiber that does the cleaning–not the volume of the food, which gets mashed up and partially liquefied early on in the digestive process. Therefore, the pills “work” by replacing the fiber that foods contain.

[Indistinguishable]

In that case, given that the mechanism of the fiber can’t really be “large volume of indigestible stuff moves along the GI tract and wipes it clean”, per se, what is the mechanism of its action?

[Gfactor]

Fiber is the portion of plants that is not digested
or absorbed by the human body. As fiber passes
through the digestive tract, it affects the rate at
which food leaves the stomach, the absorption
of nutrients, and the movement of waste
products through the colon.
Generally, soluble fiber does its work at the
beginning of the digestive system. It slows the
rate at which certain nutrients are absorbed from
the stomach and small intestine. Insoluble fiber
does its work at the end of the digestive system.
It speeds up the rate at which waste products
travel through the colon and are removed from
the body.

http://www.studentaffairs.cmu.edu/healthservices/nutrition/fiber.pdf

[Sapo]

Thanks for the responses. My diet is big on veggies and greens, so I am just having a hard time equating a little pill to the amount of plants in my plate, as much as I know that is mostly water. How many grams of fiber in a regular pill? What’s the FDA recommended daily intake? How does that translate into, say lettuce.

ETA: oops, most of that is answered in the links provided.

[Gfactor]

fiber based on 11.5 g of fiber per 1,000 calories.

http://www.fda.gov/FDAC/special/foodlabel/dvs.html

1 cup of iceberg lettuce has about .7 grams of fiber; 1 cup of romaine lettuce has 1 gram.

Iceberg Lettuce Nutrition Facts and Health Benefits