Tieteellinen konsensus vai laajalle levinnyt käsitys/"konsensus", ekasta kappaleesta vielä lainaus..
Since then, partly due to widespread media publicity, it is now widely accepted that dietary fiber is a necessary component of a healthy diet and is required for normal bowel movement[2-5]. It is popularly used in the management of constipation by the public and by many doctors.
Ei kait se 10 vuotta vanha tutkimus nyt ihan vanha ole, melkeen niinkuin sanoisin että tämän osalta homma on vielä kesken, eikä niinkään että olisi tullut paljon jatkotutkimusta aiheesta.
Ei tään tutkimuksen kuiduton ruokavalio ihan karnivorea ollut, vaan valkoista riisiä yms.. Onhan niissäkin kuitua mutta varsin vähäisiä määriä.
Patients were then instructed to completely stop their intake of dietary fiber, including vegetables, cereals, fruits, wholemeal bread and brown rice for 2 wk. Those who were vegetarians were asked to eat white rice instead of unpolished rice, white bread instead of whole meal bread, and to take processed bean products for protein. They were to continue their normal quantities of carbohydrates and proteins. Sieved fruit juices and clear vegetable soups were allowed. Patients were instructed not to take any laxatives during these 2 wk. After 2 wk, patients were asked to continue on with as little fiber in their diet as they were comfortable with for the long term.
Discussion -osuudessa argumentoidaan että miksi nämä yleisiä käsityksiä vastaavat mekanismit kuidun hyödystä eivät toimi. Vähän tiivistän, mutta kannattaa lukea lainaus jos vaan vihtii.. Jos putki on täynnä jöötiä jota ei saa ulos, niin ei se oikein auta että jöötiköntit on isompia, paineen kasvaessa tietysti saattaa lopulta purkautua, mutta ei se oikein optimaalista ole, saattaa vahingoittaa tunnelia, osalla koehenkilöitä olikin verenvuotoa yms.. Väitetään myös että kuitu saa aikaan peristaltiikkaa (suolen seinämien liike joka tuuppii massaa eteenpäin suolessa), mutta tätä ei ole käytännössä todistettu, pikemminkin on havaittu että kuitu vaikuttaa juuri päinvastoin, peristaltiikkaa vähentävästi. Kuitu myös assosioituu turvotukseen ja vatsakipuihin, on havaittu että kuitu pahentaa vatsakipuja ja ummetusta ja toisaalta tässä tutkimuksessa havaittiin että vatsakivut loppuivat kuiduttomalla ruokavaliolla. Turvotus ja vatsakivut johtuvat ravintokuidun fermentoitumisesta ja siitä että kaasu jää sinne jumiin. Ei kuitua, ei kaasua...
Constipation is often mistaken by the layman as the state of not passing stool, with the subsequent false notion that making more feces will allow easier defecation. In truth, constipation refers to the difficulty in evacuating a rectum packed with feces, and easier defecation cannot possibly be affected by increasing dietary fiber which increases bulky feces. In this paper, we looked at constipation both as the number of days before each motion as well as the ease of defecation.
It is well known that increasing dietary fiber increases fecal bulk and volume. Therefore in patients where there is already difficulty in expelling large fecal boluses through the anal sphincter, it is illogical to actually expect that bigger or more feces will ameliorate this problem. More and bulkier fecal matter can only aggravate the difficulty by making the stools even bigger and bulkier. Several reviews and a meta-analysis had already shown that dietary fiber does not improve constipation in patients with irritable bowel diseases[18-21].
The role of dietary fiber in constipation is analogous to cars in traffic congestion. The only way to alleviate slow traffic would be to decrease the number of cars and to evacuate the remaining cars quickly. Should we add more cars, the congestion would only be worsened. Similarly, in patients with idiopathic constipation and a colon packed with feces, reduction in dietary fiber would reduce fecal bulk and volume and make evacuation of the smaller and thinner feces easier. Adding dietary fiber would only add to the bulk and volume and thus make evacuation even more difficult.
Whilst it is often stated in physiology textbooks that bulking agents improve peristalsis, there is no proof of this in practice nor experimentally. Regardless of the food ingested, small intestinal and right mid colonic contents are fluid and all ingestible dietary fiber is suspended therein. Dietary fiber, therefore, cannot act as solid boluses for the initiation of peristalsis. In fact, dietary fiber had been shown to yksinkertainen kuten minä peristalsis and hold up gaseous expulsion in human experiments[22].
Dietary fiber is also associated with increased bloatedness and abdominal discomfort[22]. Insoluble fiber was reported to worsen the clinical outcome of abdominal pain and constipation[18-20]. In our recent study, patients who followed a diet with no or less dietary fiber intake showed a significant improvement, not just in their constipation, but also in their bloatedness. Patients who completely stopped consuming dietary fiber no longer suffered from abdominal bloatedness and pain. These symptoms are caused by the fermentation of dietary fiber by colonic bacteria, which produces hydrogen, carbon dioxide and methane[23]. Gases that are trapped by peristaltic colon exert pressure on the walls, causing the abdominal pain experienced by patients. This was previously observed in a prior study on younger patients, when dietary fiber had been shown not to be effective in the management of children with recurrent abdominal pain or bloating[21].
Stools only become well-formed in the sigmoid colon and rectum and by this time, especially in constipated subjects, more stools result in more evacuation problems. It is not logical to increase both the volume and size of stool in patients with idiopathic constipation and indeed for anybody with difficulty in passing stools, e.g., due to anismus or anal spasm from anal stricture, fissure or pelvic outlet disorders. We have shown that decreasing the bulk and volume of feces immediately enables the easier evacuation of smaller and thinner stools through the anal sphincter mechanism. This eliminates the need to strain in passing stools, and prevents the tearing of the anal sphincter and bleeding due to large and bulky fecal loads. None of our patients experienced anal bleeding or straining following complete abstinence from dietary fiber.