Thanks for your reply. I went back and reviewed the source material . Certainly your point has merit. The fiber requirements for a liquid diet may differ with regard to laxation and gastric distress. A lower fiber diet, though, does seem to forego some of the protection against cardiovascular disease and colon cancer. Quoting from the source:
In the Health Professionals Follow-Up Study (Rimm et al., 1996), there is a difference of 16.5 g of fiber intake between the highest and lowest intake groups (28.9–12.4), and a reported relative risk of 0.45 for fatal coronary disease and 0.59 for total myocardial infarction for men in the highest compared to the lowest quintile for fiber intake. This equates to a risk reduction of 3.3 percent/g of fiber for fatal coronary disease and 2.5 percent/g of fiber for total myocardial infarction. In the Nurses’ Health Study (Wolk et al., 1999) there is a difference of 11.4 g of fiber between the highest and lowest intake groups (22.9–11.5) and a relative risk of 0.77 for total CHD. This equates to a risk reduction of 2.02 percent/g of fiber. Finally, in a study of Finnish men (Pietinen et al., 1996), there is a difference of 18.7 g of fiber between the highest and lowest intake groups (34.8–16.1) and a relative risk of 0.68 for coronary death. This equates to a risk reduction of 1.71 percent/g of fiber.
Lanza (1990) reviewed 48 epidemiological studies on the relationship between diets containing Total Fiber and colon cancer and found that 38 reported an inverse relationship, 7 reported no association, and 3 reported a direct association. In the Netherlands, Dietary Fiber intake was reported to be inversely related to total cancer deaths, as the 10-year cancer death rate was approximately threefold higher in individuals with low fiber intake compared with high fiber intake (Kromhout et al., 1982). Despite these and other positive findings, a number of important studies (Fuchs et al., 1999; Giovannucci and Willett, 1994) and three recent clinical intervention trials (Alberts et al., 2000; Bonithon-Kopp et al., 2000; Schatzkin et al., 2000) do not support a protective effect of Dietary Fiber intake against colon cancer. This issue remains to be resolved.
The source leaves it open even with that set of studies; the animal studies strongly suggest an effect. See e.g. .
So in short, fiber’s good, not all fiber has an effect on laxity and gastric distress, it may just be a question of finding the right blend to support a liquid diet. Preparation may matter here too, less finely ground powders may digest more slowly reducing the flatulence issue; the blend will just have to be empirically tested. But for long term health, flatulence << (colon cancer, heart problems). Let me know if I’ve missed anything.
 Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat,
Fatty Acids, Cholesterol, Protein, and Amino Acids, http://www.nap.edu/download.php?record_id=10490#