Short‐chain fatty acid content and pH in caecum of rats given various sources of carbohydrates

Abstract

The caecal content of short-chain fatty acids (SCFA; acetic, propionic and butyric acid), caecal pH, fermentability and dry matter digestibility (DMD) were examined through balance experiments in rats fed 1 1 various indigestible carbohydrates. The following carbohydrate sources were incorporated into test diets: cellulose, oat husk, wheat bran, oat bran, pea fibre, linseed fibre, low methoxylated (LM)-pectin. guargum, 8-glucans, neosugar and raffinose. The indigestible carbohydrates, except for those in wheat bran, oat husk and cellulose, were highly fermented, ie > 90%. Caecal pH varied between 5.6 and 7.8, with neosugar and raffinose causing the lowest pH and the fibre-free diet and the diet with oat husk the highest. The caecal pool sizes of SCFA were highest with raffinose, P-glucans, LM-pectin, guargum and linseed fibre (335400 pmol) while pea fibre, wheat bran, oat bran and neosugar gave intermediate levels (137-227 pmol). The pool size with oat husk and cellulose was similar as with the basal diet ( 4 M 4 pmol). A high proportion of propionic acid was obtained with guargum and linseed fibre, whereas acetic acid was the predominant product in case of LM-pectin. On the other hand, linseed fibre gave a remarkably low proportion of butyric acid. The quantity fermented and caecal pH correlated well to the amount of SCFA with most materials (r = 0.96 and r = -0.87, respectively), an exception was neosugar and in case of fermentability also oat bran. DMD values with most of the easily fermented carbohydrates were high (> 96 YO).Exceptions were diets with P-glucans and oat bran which caused low DMD values, about 93 YO. It is concluded that indigestible carbohydrates may differ in ability to lower caecal pH and to form SCFA during fermentation.

Effect of psyllium on gastric emptying, hunger feeling and food intake in normal volunteers: a double blind study

“…Indeed an increase in the viscosity of food may have several effects: (a) to slow down the small intestinal transit (Low, 1988;Cherbut et al, 1994); but Cummings et al (1979) did not ®nd any modi®cation of oro-cecal transit time with pectin; (b) to reduce the interaction between food nutrients and digestive enzymes (Flourie  et al, 1984;Cummings et al, 1979; to increase the time for nutrient diffusion, by increasing the thickness of the unstirred water layer (Flourie  et al, 1984;Rydning & Berstad, 1986). This is consistent with the studies which have demonstrated that soluble ®bres could decrease the area under the curve of serum glucose after a duodenal glucose load (Berggren et al, 1993). This is also consistent with our own study: serum insulin response to the test meal, and postprandial serum glucose and triglycerides levels were of less magnitude during the psyllium session than during the placebo one.…”

“…This is also consistent with our own study: serum insulin response to the test meal, and postprandial serum glucose and triglycerides levels were of less magnitude during the psyllium session than during the placebo one. But it could also be related to motor or metabolic actions of psyllium, such as increase in the production of short chain fatty acids by the large bowel in response to the dietary ®bre ingestion (Berggren et al, 1993). This needs further investigation.…”

Effects of inulin supplemented to cellulose-free or cellulose-rich diets on caecal environment and biochemical blood parameters in rats

“…Purified cellulose has been considered to be a diet's diluent, whereas the other complex carbohydrates are more likely to be extensively degraded by the caecal microflora into SCFA (Juśkiewicz et al, 2005). All SCFA are claimed to act as trophic agents on caecal/colonic epithelium, but butyric seems to be the most and propionic the least efficient (Berggren et al, 1993). Another possible way of increased epithelium proliferation was indicated in a study by Whiteley et al (1996).…”

Dietary supplementation with β-glucan enriched oat bran increases faecal concentration of carboxylic acids in healthy subjects

“…Different types of indigestible carbohydrates give rise to different amounts and patterns of CAs during colonic fermentation, and it may therefore be possible to regulate the CA formation by diet. The CAs formed may depend on for example the monomeric composition of the carbohydrates, the type of linkages between the carbohydrate monomers, their solubility and their molecular weight (Berggren et al, 1993;Casterline et al, 1997;Bird et al, 2000;Karppinen et al, 2000;Henningsson et al, 2002Henningsson et al, , 2003Nilsson and Nyman, 2005). Studies examining CA formation have mainly been conducted in vitro by using human faecal inocula, or in vivo using animal models.…”

“…Studies examining CA formation have mainly been conducted in vitro by using human faecal inocula, or in vivo using animal models. The rat is the most common model when studying the CA formation in vivo, although there are also some studies available in pigs (Berggren et al, 1993;Roland et al, 1995;Brown et al, 1997;Djouzi and Andrieux, 1997;Bird et al, 2000;Henningsson et al, 2002Henningsson et al, , 2003Nilsson and Nyman, 2005). Studies in man have mainly been performed by measurements of CAs in faeces and have been questioned on the premises that such measurements do not give information regarding the formation of CAs in proximal colon where most of the fermentation actually takes place.…”