Effect of dietary phytase on the digestion of phytate in the stomach and small intestine of humans

The purpose of this study was to investigate whether dietary phytase is involved in the hydrolysis of phytate in the stomach and small intestine of humans. The digestibility of phytase-deactivated wheat bran was studied on eight occasions and untreated wheat bran on two occasions in healthy ileostomates. Five subjects were studied for two 4-d periods and one subject on two occasions for two 4-d periods while fed a constant low fiber diet. The low fiber diet was supplemented with 16 g/d wheat bran in the second period. Three other subjects fed a low fiber diet were studied for 10 consecutive days, bran being added to the diet on d 5, 6 and 7. Inositol hexaphosphate and its degradation products were analyzed with a recently developed HPLC method. On average, 95% of the ingested phytate from phytase-deactivated wheat bran and 40% of the ingested phytate from untreated wheat bran were recovered in ileostomy contents. These results differ from those of a previous analysis using an iron precipitation method. Mucosal phytase and alakaline phosphatase, if present in the human small intestine, do not seem to play a significant role in phytate digestion in humans, whereas the dietary phytase may be an important factor for phytate hydrolysis. Iron precipitation methods are not adequate for determinations of phytate digestion.     

The effect of wheat bran on the absorption of minerals in the small intestine

1. Studies on mineral absorption were carried out in ileostomy patients using the metabolic balance technique. The effect of wheat bran on the absorption of phosphorus, calcium, magnesium, zinc and iron was studied. The extent of digestion of bran phytate in the stomach and small intestine was also investigated. 2. Eight patients with well established conventional ileostomies were studied during two periods while on a constant low-fibre diet. In the second period, 16 g wheat bran/d (American Association of Cereal Chemists) was added to the diet. The amount of phytate-P, non-phytate-P, Ca, Mg, Zn and Fe was determined in the ileostomy contents and in duplicate portions of the diet. 3. Of the added bran phytate-P 24-61% was recovered in the ileostomy contents. In the bran period a significantly decreased amount of Zn was absorbed, while the apparent absorption of Fe and phytate-P increased and that of non-phytate-P, Ca and Mg remained constant. Due to the mineral content of bran, the relative absorption differed in some respects from the absolute absorption, being decreased for Zn, Mg and phytate-P but unchanged for Ca, Fe and non-phytate-P. 4. It is concluded that phytate is partly digested in the stomach and small intestine or possibly absorbed. Addition of 16 g bran/d to the diet does not seem to impair the mineral absorption from the small intestine except that of Zn.     

Bioavailability to rats of iron and zinc in wheat bran: response to low-phytate bran and effect of the phytate/zinc molar ratio

Low-phytate wheat bran was produced by enzymatic hydrolysis and extraction. Rat bioassay methods were utilized to determine bioavailability of iron and zinc in the low-phytate brans and to study the effect of dietary phytate/zinc molar ratio on zinc bioavailability when the phytate source was bran. Endogenous phytase activity hydrolyzed 80-100% of the phytate when wheat bran was incubated in water overnight. The relative biological values of the iron in raw bran and phytate-free bran were 98 and 113, respectively, compared to 100 for ferrous ammonium sulfate in a hemoglobin repletion assay. Low-phytate brans with phytate/zinc molar ratios of 8 or less were equivalent to zinc sulfate as dietary sources of zinc for growth of rats. Rats fed diets that contained wheat bran with zinc sulfate added to reduce the dietary phytate/zinc molar ratio from 40 or 50 to 20 grew at the same rate as rats fed a phytate-free diet, but femur zinc values were lower than those in the reference group. Gel filtration chromatography of extracts of raw and low-phytate brans suggested that zinc might be associated with phytate in wheat bran.     

Effects of dietary cellulose, pectin and oat bran on the small intestine in the rat

The present study was undertaken to determine if three sources of dietary fiber would alter length, weight, DNA, protein or enzyme activity in the small intestine since various fibers are known to decrease intestinal absorption. Rats were fed semipurified diets that contained either 20% cellulose (C), 20% oat bran, 5% pectin (P) or no fiber source (FF). Leucine aminopeptidase activity were significantly greater in the P and C groups when compared with the FF group. There were no significant differences in sucrase activity. Animals in the P group had heavier and longer small intestine and heavier mucosa than the FF group. There were no significant differences in total mucosal DNA or protein. These results indicate that two sources of dietary fiber, cellulose and pectin, can change leucine aminopeptidase activity in the small intestine.     

Reduction of the phytate content of bran by leavening in bread and its effect on zinc absorption in man

The effect of leavening of bread containing bran on the phytic acid content and on zinc absorption in man was studied. Twenty breads with leavening times varying from 0 to 120 h were prepared. The breads contained 250 g wheat bran/kg flour. The phytic acid content was determined after baking. The phytic acid content of bread containing bran was reduced to about 40% after 2 h of leavening and to 15% after 2 d. No further decrease was observed. Zn absorption from single meals was determined using a radioisotope technique. Forty-two students volunteered for these studies. They were served a breakfast of milk, butter, bread and 10, 16 or 30 g bran served either raw or baked into the bread with fermentation times of 15 min, 45 min, 3 h or 16 h. One meal contained no bran, but phytate and Zn were added in amounts equivalent to the content of 10 g bran. The amount and percentage of Zn absorbed increased at each bran level as fermentation was prolonged. The percentage of Zn absorbed was reduced by increased bran content in the meal. It is concluded that the fermentation of bread containing bran reduces the phytic acid content and increases Zn absorption from such bread. This may be of importance to people subjected to diets with a high cereal content, especially in combination with a low animal-protein intake.     

The effect of decortication and extrusion on the digestibility of sorghum by preschool children

The effect of decortication and extrusion on the apparent protein quality and digestibility of sorghum (S. vulgare) was evaluated in comparative balance studies in nine children 7-24 months of age. Sorghum provided (as kilocalories) 8% protein and 62% carbohydrate in the study diet. Lysine was supplemented to 3% of protein. Casein provided 6.4% protein kilocalories in the control diet. A mixture of sucrose, dextrimaltose and cornstarch provided carbohydrate. Both diets contained 30% fat kilocalories as soybean-cottonseed oil blend. Balance studies were carried out during the last 6 days of three 9-day dietary periods: control-sorghum-control. Apparent N absorption from sorghum was 81 +/- 4% and did not differ from control. Apparent N retention, 21 +/- 6%, was expectedly lower than the preceeding control (27 +/- 8%, P less than 0.05) and following control (33 +/- 7%, P less than 0.01) values. The control values differed significantly from each other (P less than 0.05). Fecal weights and energy losses showed only minor differences between the two diets. These data contrast sharply with previous results obtained with whole-grain sorghum and suggest that the use of decortication and low cost extrusion processing can markedly improve the apparent protein quality and digestibility of sorghum.     

Starch digestion rate in the small intestine of broiler chickens differs among feedstuffs

Dietary starch is the major energy source for broiler chickens, and knowledge about its digestive behavior can be important. In a digestibility trial with 720 broiler chickens, site, rate and extent of starch digestion were measured for 12 feedstuffs. Starch digestion was determined using the slaughter technique, which involves removal of the small intestine from the recently killed chicken, with manual collection of the contents. Starch digestion coefficients were calculated from remaining starch in three segments of the small intestine and in excreta. Mean retention time in four segments of the small intestine was measured. This enabled calculations for starch digestion rate (k(d)). Ileal starch digestibility varied from 33% (potato starch) to 99% (tapioca). Retention time for digesta in the postduodenal small intestine varied from 136 min (barley diet) to 182 min (potato diet). On the basis of starch digestion rates, a distinction was made between slowly digestible starch (k(d) < 1 h(-1)), gradually digestible starch (k(d):1-2 h(-1)) and rapidly digestible starch (k(d) > 2 h(-1)). Starch from common beans was digested most slowly (k(d): 0.5 h(-1)), and starch from tapioca was digested most rapidly (k(d): 4.3 h(-1)). Starch digestion rates of potato starch and legume seeds were lower than those of cereal grains and tapioca. Degradation of starch entering the hind gut of the birds did not occur. Milling of corn affected rate, but not the extent of starch digestion. We concluded that site of starch digestion within the small intestine is not an accurate indicator for starch digestion rate.     

Wheat bran and wheat germ: effect on digestion and intestinal absorption of dietary lipids in the rat

We investigated the effects of fiber-rich wheat bran and wheat germ on dietary fat and cholesterol assimilation. Rats were given a test meal containing [14C]triolein and [3H]cholesterol. After various digestion periods, addition of the wheat fractions (10% of meal solids) did not modify the lipid gastric emptying rate. Gastric and intestinal triglyceride lipolysis was significantly reduced when wheat fractions were present. The mucosal uptakes of [14C]lipids and [3H]cholesterol were significantly modified by the wheat fractions after 1 and 2.5 h. No shift in the site of intestinal absorption and no change in the distribution of labeled lipid in the intestinal mucosa was observed. Plasma [14C]lipids and [3H]cholesterol were significantly decreased by both wheat fractions whereas these increased cecal accumulation of dietary lipids and cholesterol. Thus wheat bran and wheat germ alter fat and cholesterol processing in rats. A mechanism of action accounting for the data observed in proposed.     

Decomposition of wheat bran and ispaghula husk in the stomach and the small intestine of healthy men

Decomposition of dietary fibers in the stomach and small bowel was studied in 13 healthy male volunteers. Liquid control meals were compared with test meals, which in addition contained a source of fiber (wheat bran or ispaghula husk) in random order. Aspirations were collected from the stomach, the proximal jejunum, the mid gut and the terminal ileum. Radiolabeled polyethylene glycol-4000 was used as nonabsorbable water-phase marker, and the formation of free arabinose was used to quantify the hydrolysis of dietary fibers. Ingested fibers, aspirates and urine specimens were analyzed for monosaccharides, either free or fiber-bound, by gas-liquid chromatography. Both types of fiber were hydrolyzed in the stomach, but not in the small bowel. Of ispaghula husk, 1-6% was hydrolyzed, as was 5-8% of wheat bran. Intestinal absorption of free arabinose was 85-93%, but excretion of arabinose in the urine was not greater than after control meals. For further evaluation of gastric hydrolysis six additional healthy male volunteers were studied by serial aspirations from the antral part of the stomach. Hydrolysis was instantaneous for both fibers, and was significantly more pronounced for wheat bran than for ispaghula husk.     

The effect of different levels of wheat bran on iron absorption in rats from bread containing similar amounts of phytate

1. Iron absorption was studied in weanling rats using balance techniques from semi-synthetic diets containing dried white bread (60.5 g dietary fibre/kg. White & Southgate, unpublished results), brown bread (130.2 g dietary fibre/kg) or wholemeal bread (221.2 g dietary fibre/kg) at a level of 300 g/kg and compared with a control group given a diet containing added FeSO4 at a similar Fe level to that for the bread groups. The dried bread contained 6.2-6.4 g phytate/kg. 2. Absorption of Fe was significantly higher (P less than 0.001) in the control group (0.45) than in the White (0.28), brown (0.31) or wholemeal (0.24) groups. 3. A second experiment was carried out on 6-week-old rats in which the dried bread was extrinsically labelled with 59Fe and absorption from a single meal measured by both faecal excretion and incorporation of 59Fe into the blood. Control animals were given 59FeSO4 for comparison. 4. The excretion of 59Fe (% of administered dose) was significantly lower (P less than 0.001) in the control group (31) than in the white (48), brown (45) or wholemeal (47) groups. After 10 d the control group had significantly more 59Fe in the blood than the bread groups, but there were no differences between the bread groups. 5. It appears that wheat bran fibre itself has no effect on the retention of Fe from the diet in the rat, when supplied in amounts similar to those found in commercially-available bread.     

Dietary protein absorption of the small intestine in human neonates

Background: The intestine plays a key role in the absorption of dietary proteins, which determines growth of human neonates. Bowel resection in the neonatal period brings loss of absorptive and protective surface and may consequently lead to malabsorption of dietary nutrients. However, there are no data on net dietary protein absorption of the small intestine in the period after intestinal surgery in human neonates. We therefore evaluated dietary feeding tolerance and quantified net dietary protein absorption capacity of the small intestine in human neonates in whom a temporary jejunostomy or ileostomy was created. Methods: Seventeen patients were included in the study. We collected small intestinal outflow fluid at the level of the enterostomy weekly for 24–48 hours during weeks 3 through 6 postoperatively. Protein levels in the intestinal outflow fluid were determined by bicinchoninic acid (BCA) assay. Results: In 14 patients, an enteral intake of >100 mL/kg/d was reached at a median of 17 days (range, 8–32 days) postoperatively. Three patients did not reach this level within the study period. Overall, the net dietary protein absorption capacity was 70%–90% of the total enteral protein intake. Conclusions: This study demonstrates that the dietary protein absorption capacity of the small intestine is intact in most human neonates after intestinal surgery in a very critical period of their lives. Furthermore, our results do not support the use of hydrolyzed or elemental formula in newborns with an enterostomy to improve amino acid uptake.     

Trophic effect of bee pollen on small intestine in broiler chickens

In this study, the effects of bee pollen on the development of digestive organs were evaluated in broiler chickens. A total of 144 1-day-old AA broiler chickens were randomly and equally divided into two groups, assigned as the control group and the pollen group, respectively. The control group was fed with a basic diet, while the pollen group was fed with a basic diet supplemented with 1.5% bee pollen over a period of 6 weeks. At the end of each week, the digestive organs were obtained for comparison from 12 broilers randomly selected from each group. The results demonstrated that compared to the control group, the small intestine villi from the duodenum, jejunum, and ileum were longer and thicker in the pollen group. This difference was more significant during early development, especially through the first 2 weeks. Bee pollen increased the length of the villi by 37.1% and 29.4% in the duodenum, 28.1% and 33.7% in the jejunum, and 18.6% and 16.2% in the ileum in week 1 and 2, respectively. Furthermore, the small intestinal glands were developed at a higher density in the pollen group, and the depth of the glands was significantly increased by bee pollen in the first 2 weeks. These findings suggest that bee pollen could promote the early development of the digestive system and therefore is a potentially beneficial food supplement for certain conditions, such as short bowel syndrome.     

Absorption of triglyceride by human small intestine: dose-response relationships

Healthy subjects with ileostomies (ileostomates) were fed six breakfasts of 5-100 g linseed oil. This lipid source was chosen so that linolenic acid could be used as a fatty acid probe. Phenol red was included in the meal so that mouth-to-stoma transit could be measured as the t 1/2 of phenol red. Ileostomy effluent was collected over 24 h and the dose of lipid ingested was related to lipid output and to intestinal transit time. The coefficient of variation for mouth-to-stoma transit was less than 12%. The slopes of the least-square lines relating lipid ingested to lipid output and to mouth-to-stoma transit time were positive and significantly different (p less than 0.05) from 0. The ileostomate's small intestine absorbed linolenic acid with 98% efficiency. A delay in mouth-to-ileum transit, associated with increasing lipid loads, is one obvious mechanism that maintains the intestine's absorptive efficiency.