Anja Serena

New insight into butyrate metabolism.

Butyrate is a C4 acid produced by microbial fermentation of carbohydrates and protein in the large intestine of all animal species. The factor of prime importance for the production rate of butyrate in the lower gut is type and levels of non-digestible carbohydrates entering the large intestine. It was previously believed that 85-90 % of the butyrate produced in the gut was cleared when passing the gut epithelium, but recent studies with catheterised pigs have shown that the concentration of butyrate in the portal vein is strongly influenced by the production rate in the large intestine. Increased gut production of butyrate further raises the circulating level of butyrate. For good reason it is not possible with current technologies to perform direct measurements of the variation in the butyrate concentration in the portal vein of human subjects, but short-chain fatty acid levels in portal blood from sudden-death victims, subjects undergoing emergency surgery or planned surgery have indicated a higher gut production and absolute and relative concentration of butyrate in non-fasted as compared with fasted human subjects. However, despite an expected higher gut production of butyrate when feeding a high-fibre rye-bread-based diet as compared with a low-fibre wheat-bread-based diet, there was no difference in absolute or relative levels of butyrate in the peripheral blood of human subjects.

The role of whole-wheat grain and wheat and rye ingredients on the digestion and fermentation processes in the gut--a model experiment with pigs.

The effect of wheat and rye breads made from white wheat flour with added refined fibre (WFL), whole-wheat grain, wheat aleurone flour (WAF) or rye aleurone flour (RAF) on digestion and fermentation processes in the gut was studied in a model experiment with pigs. The diets were similar in dietary fibre (DF) but differed in arabinoxylan (AX) content and composition. Twenty pigs were fed the breads three times daily (08.00, 13.00 and 18.00 hours) and the digesta collected through a T-cannula for two successive periods (breakfast: 8.00-13.00; lunch: 13.00-18.00 hours). Faeces were collected for 24 h and caecal and colonic contents at slaughter. The rigid nature of the aleurone cell walls encapsulated nutrients, which resulted in reduced (P < 0.01) digestibility of protein (WAF and RAF breads) and fat (RAF bread). For the RAF bread, the digestibility of starch was also lower (P < 0.001) than of the wheat-based diets primarily due to the higher intestinal viscosity. The DF composition had an impact on (P < 0.001) the site for fibre degradation in the large intestine. Thus, AX of the WAF bread, with the lowest degree of substitution, were fermented as much in the caecum as in the colon, whereas AX of the RAF bread, with an intermediary degree of substitution, were mainly fermented in the caecum. The WFL bread, rich in cellulose, was fermented more distally. Fermentation of experimental breads in the large intestine had no effect (P>0.05) on the production of metabolites, except for butyrate which was higher (P < 0.01) after the WAF bread consumption.

Digestion of carbohydrates and utilization of energy in sows fed diets with contrasting levels and physicochemical properties of dietary fiber.

Three experimental diets were used to investigate the digestion of carbohydrates and utilization of energy in sows fed diets with different levels and physicochemical properties of dietary fiber (DF). The low-fiber diet (LF; DF, 16%; soluble DF, 4.8%) was based on wheat and barley. The high-fiber 1 diet (HF1; DF, 41%; soluble DF, 11%) was based on wheat and barley supplemented with the coproducts: sugar beet pulp, potato pulp, and pectin residue, and the high-fiber 2 diet (HF2; DF, 44%; soluble DF, 7.3%) was based on wheat and barley supplemented with approximately 1/3 of the coproducts used in diet HF1 and 2/3 of brewers spent grain, seed residue, and pea hull (1:1:1, respectively). The diets were studied in 2 series of experiments. In Exp. 1, the digestibility and ileal and fecal flow of nutrients were studied in 6 ileal-cannulated sows placed in metabolic cages designed as a repeated 3 x 3 Latin square design. In Exp. 2, energy metabolism was measured in respiration chambers using 6 sows in a repeated 3 x 3 Latin square design. The DF level influenced the ileal flow of most nutrients, in particular carbohydrates, which increased from 190 g/d when feeding the LF diet to 538 to 539 g/d when feeding the HF diets; this was also reflected in the digestibility of OM and carbohydrates (P < 0.05). The ranking of total excretion of fecal materials was HF2 > > HF1 > LF, which also was reflected in the digestibility of OM, protein, and carbohydrates. Feeding HF diets resulted in greater CH(4) production, which was related to the amount of carbohydrates (r = 0.79) and OM (r = 0.72) fermented in the large intestine, but with no difference in heat production (12.2 to 13.1 MJ/kg of DM). Retained energy (MJ/kg of DM) was decreased when feeding HF1 compared with LF and negative when feeding HF2. Feeding sows HF1 reduced the activity of animals (5.1 h/24 h) compared with LF (6.1 h/24 h; P = 0.045).

Absorption of carbohydrate-derived nutrients in sows as influenced by types and contents of dietary fiber.

The current investigation was undertaken to study the absorption and plasma concentration of carbohydrate-derived nutrients [glucose, short-chain fatty acids (SCFA), and lactate] and the apparent insulin production in sows fed diets containing contrasting types and contents of dietary fiber. Six sows were fed 3 experimental diets, low fiber (LF; 177 g of dietary fiber and 44 g of soluble fiber/kg of DM), high soluble fiber (HF-S; 429 g of dietary fiber and 111 g of soluble fiber/kg of DM), and high insoluble fiber (HF-I; 455 g of dietary fiber and 74 g of soluble fiber/kg of DM), in a repeated crossover design. Variations in dietary concentration and solubility of dietary fiber were obtained by substituting starch-rich wheat and barley in the LF diet with dietary fiber-rich co-products (sugar beet pulp, potato pulp, pectin residue, brewers spent grain, pea hulls, and seed residue, which have distinct physicochemical properties). The main carbohydrate component of the LF diet was starch and nonstarch polysaccharides (cellulose and noncellulosic polysaccharides) for the 2 high dietary fiber diets. Consumption of the LF diet resulted in increased and rapid glucose absorption at 0 to 4 h postfeeding. With the HF-I diet, the glucose absorption pattern was similar but at a decreased rate, whereas it was decreased and delayed with the HF-S diet (diet, P < 0.001; time, P < 0.001). These differences were also reflected in the insulin response. The quantitative absorption of SCFA at 0 to 10 h postfeeding was greater when feeding the HF-S diet compared with the LF diet (P < 0.001) and intermediate when feeding the HF-I diet (P < 0.001). The study showed that feeding the high dietary fiber diets resulted in a increased and more uniform uptake of SCFA than when feeding the LF control. Moreover, the HF-S diet reduced diurnal variation in glucose and insulin concentrations.

NMR-based metabonomic studies reveal changes in the biochemical profile of plasma and urine from pigs fed high-fibre rye bread.

This study presents an NMR-based metabonomic approach to elucidate the overall endogenous biochemical effects of a wholegrain diet. Two diets with similar levels of dietary fibre and macronutrients, but with contrasting levels of wholegrain ingredients, were prepared from wholegrain rye (wholegrain diet (WGD)) and non-wholegrain wheat (non-wholegrain diet (NWD)) and fed to four pigs in a crossover design. Plasma samples were collected after 7 d on each diet, and 1H NMR spectra were acquired on these. Partial least squares regression discriminant analysis (PLS-DA) on spectra obtained for plasma samples revealed that the spectral region at 3.25 parts per million dominates the differentiation between the two diets, as the WGD is associated with higher spectral intensity in this region. Spiking experiments and LC-MS analyses of the plasma verified that this spectral difference could be ascribed to a significantly higher content of betaine in WGD plasma samples compared with NWD samples. In an identical study with the same diets, urine samples were collected, and 1H NMR spectra were acquired on these. PLS-DA on spectra obtained for urine samples revealed changes in the intensities of spectral regions, which could be ascribed to differences in the content of betaine and creatine/creatinine between the two diets, and LC-MS analyses verified a significantly lower content of creatinine in WGD urine samples compared with NWD urine samples. In conclusion, using an explorative approach, the present studies disclosed biochemical effects of a wholegrain diet on plasma betaine content and excretion of betaine and creatinine.

Products deriving from microbial fermentation are linked to insulinaemic response in pigs fed breads prepared from whole-wheat grain and wheat and rye ingredients

The effects of wheat and rye breads made from whole-wheat grain (WWG), wheat aleurone flour (WAF) or rye aleurone flour (RAF) on net portal absorption of carbohydrate-derived nutrients (glucose, SCFA and lactate) and apparent insulin secretion were studied in a model experiment with catheterised pigs. The breads were similar in dietary fibre (DF, 120-125 g/kg DM) but differed in arabinoxylans (50-62 g/kg), β-glucans (4-9 g/kg) and content of soluble DF (13-29 g/kg). Six pigs in a repeated 3 × 3 crossover design were fitted with catheters in the portal vein and the mesenteric artery and a portal flow probe. Pigs were fed three meals daily (at 09.00, 14.00 and 19.00 hours), and blood profiles were collected repeatedly from 08.30 until 19.00 hours once weekly. Net portal absorption of glucose was similar among breads and between meals. In contrast, insulin secretion was lowest (P < 0·05) in pigs fed RAF bread (3·9 nmol/h), intermediate in pigs fed WAF bread (5·4 nmol/h) and highest in pigs fed WWG bread (5·9 nmol/h), indicating that RAF bread improved insulin economy. Portal concentrations of propionate, butyrate and valerate were high, intermediate and low (P < 0·05) when pigs were fed RAF, WAF and WWG breads, respectively. Insulin secretion was higher (P < 0·001), and portal absorption of SCFA was lower (P < 0·05) after the first daily meal than after the second daily meal (8·8 v. 4·4 nmol/h). A low insulin response was associated with high portal absorption of SCFA. In conclusion, RAF bread was able to improve insulin economy compared to WWG bread.

Kinetics of the appearance of cereal alkylresorcinols in pig plasma.

Alkylresorcinols (AR) are phenolic lipids found in high amounts in wholegrain wheat and rye. They may be important as bioactive components and/or biomarkers of wholegrain wheat and rye intake. AR absorption was studied with pigs during a habitual diet and after a single meal of AR-rich diet. In study 1, four pigs were fed wholegrain rye (RD) and white wheat bread (WD) for 1 week in a cross-over design. Arterial and venous AR concentrations were determined over 540 min after feeding on days 5 and 7. In study 2, four pigs were fed a synthetic, starch-based diet for 5 d, and arterial and venous AR concentrations were determined over 960 min after feeding a single meal of RD. In study 1, plasma AR concentrations after consuming RD peaked at 120 min, remained elevated between 120 and 420 min, and were re-elevated on refeeding at 480 min. In study 2, AR appeared in the plasma after 60 min, peaked at 180-240 min, and remained elevated after 960 min. The apparent elimination half-life was 3.93 h, and the maximum plasma concentration was 666 (sem 35) nmol/l. Arterial and venous plasma AR concentrations were similar, suggesting that AR are absorbed via the lymphatic system. AR concentrations in pig plasma increase rapidly after a meal containing AR, and persist in plasma for at least 5 d, indicating that AR may be a useful biomarker of wholegrain wheat and rye intake.

Influence of dietary fiber on luminal environment and morphology in the small and large intestine of sows

In this study, the effect of feeding different types and amounts of dietary fiber (DF) on luminal environment and morphology in the small and large intestine of sows was studied. Three diets, a low-fiber diet (LF) and 2 high-fiber diets (high fiber 1, HF1, and high fiber 2, HF2) were used. Diet LF (DF, 17%; soluble DF 4.6%) was based on wheat and barley, whereas the 2 high-fiber diets (HF1: DF, 43%; soluble DF, 11.0%; and HF2: DF, 45%; soluble DF, 7.6%) were based on wheat and barley supplemented with different coproducts from the vegetable food and agroindustry (HF1 and HF2: sugar beet pulp, potato pulp, and pectin residue; HF2: brewers spent grain, seed residue, and pea hull). The diets were fed for a 4-wk period to 12 sows (4 receiving each diet). Thereafter, the sows were killed 4 h postfeeding, and digesta and tissue samples were collected from various parts of the small and large intestine. The carbohydrates in the LF diet were well digested in the small intestine, resulting in less digesta in all segments of the intestinal tract. The fermentation of nonstarch polysaccharides in the large intestine was affected by the chemical composition and physicochemical properties. The digesta from pigs fed the LF diet provided low levels of fermentable carbohydrates that were depleted in proximal colon, whereas for pigs fed the 2 high-DF diets, the digesta was depleted of fermentable carbohydrates at more distal locations of the colon. The consequence was an increased retention time, greater DM percentage, decreased amount of material, and a decreased tissue weight after feeding the LF diet compared with the HF diets. The concentration of short-chain fatty acids was consistent with the fermentability of carbohydrates in the large intestine, but there was no effect of the dietary composition on the molar short-chain fatty acid proportions. It was further shown that feeding the diet providing the greatest amount of fermentable carbohydrates (diet HF1, which was high in soluble DF) resulted in significant morphological changes in the colon compared with the LF diet.