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Rice varieties with similar amylose content differ in starch digestibility and glycemic response in humans.

Three high-amylose rice varieties, IR42, IR36, and IR62, with similar chemical composition including amylose content (26.7-27.0%), were cooked under the same conditions and tested for in vitro digestibility as well as blood glucose and insulin responses in healthy human volunteers. The starch-digestion rate and the glycemic and insulin responses were the highest in IR42, followed by IR36 and, then IR62. The differences were not due to unabsorbed carbohydrate but were related to their physicochemical properties, such as gelatinization temperature, minimum cooking time, amylograph consistency, and volume expansion upon cooking. When the three varieties were cooked for their minimum cooking time, they had the same degree of gelatinization and their starch-digestion rates and glycemic responses were similar. We conclude that amylose content alone is not a good predictor of starch-digestion rate or glycemic response. Rice varieties with similar high-amylose contents can differ in physicochemical (gelatinization) properties and this, in turn, can influence starch digestibility and blood glucose response.

Adult↗

Digestion of so-called resistant starch sources in the human small intestine.

BACKGROUND: Resistant starch sources, which are only partially digested in the small intestine, can be used to increase colonic availability of short-chain fatty acids. OBJECTIVE: To study the characteristics of the fermentation of resistant starch, the digestion of resistant starch in the small intestine has to be quantified. We compared the metabolic fates of highly digestible cornstarch (DCS), Hylon VII (type 2 resistant starch), and Novelose 330 (type 3 resistant starch), which are of corn origin and, therefore, naturally enriched in (13)C. DESIGN: After administration of 40 g starch or glucose to 7 healthy volunteers, glucose and exogenous glucose concentrations in serum and (13)CO(2) excretion in breath were analyzed for 6 h. (13)C abundance in carbon dioxide was analyzed by isotope ratio mass spectrometry (IRMS) and (13)C abundance in glucose by gas chromatography-combustion IRMS. RESULTS: By comparing the area under the curve (2 h) of exogenous glucose concentration in serum ((13)C glycemic index) after intake of starch or glucose, (13)C glycemic indexes for DCS, Hylon VII, and Novelose 330 were calculated to be 82 +/- 23%, 44 +/- 16%, and 43 +/- 15%, respectively. Comparison of 6-h cumulative percentage dose recovery in breath showed that 119 +/- 28% of DCS, 55 +/- 23% of Hylon VII, and 50 +/- 26% of Novelose 330 was digested in the small intestine. CONCLUSION: The exogenous glucose response in serum and the (13)CO(2) excretion in breath can be used to estimate small intestinal digestion of resistant starch, which amounts to approximately 50%.

Adult↗

Exclusion of pancreatic exocrine secretion from intestine in the pig: existence of a digestive compensation.

The apparent digestibility of a diet was studied over a period of 87 days after ligature of the pancreatic duct, in the growing pig. Sham operated pigs were used as controls. Feces and urine collections were made during three periods of 10 days each. Mean daily gain of sham operated pigs was higher (560 g/day) than that of pancreatic duct ligated pigs (421 g/day), throughout the experiment. Within the first period (15-24 days after ligature), the apparent digestibility of nitrogen was most affected (-35.6%) while that of energy decreased by 12.1% as compared to values obtained in sham operated pigs. Nitrogen retention was similar in all pigs. Between the 1st (15-25 days) and the 3rd period (78-87 days) after exclusion of the pancreatic secretion from intestine, the apparent digestibility of nitrogen increased by 20% and that of energy by 6%, which might suggest digestive compensation. At the end of the experiment, weights of empty small intestine and liver were significantly higher in the pancreatic duct ligated pigs. The origin of the digestive compensation is discussed.

Animals↗

Effects of fiber on digestibility and transit time in dogs.

This study examines effects of variations in fiber content on nutrient assimilation, fecal output, and gastrointestinal transit time in the dog. Four normal Beagles were fed four diets in a randomized block design. The basal diet was a canned, balanced, meat-based dog food (Alpo Trio) to which added 3, 6, and 9% by weight of alpha cellulose (Solka Flok). Food intake and fecal outputs were recorded for 5-day periods. Samples of diets and fecal collections were analyzed for dry matter, nitrogen, fat, carbohydrate and ash; digestibilities were calculated. Transit times were measured by a radiographic marker technique. Fecal weight and water increased linearly; digestibility of dry matter decreased from 90 to 70% and ash from 43 to 32% with added fiber. Responses of protein, carbohydrate and fat were less pronounced but were regular; regressions of their digestibilities on added fiber were significant. Regression estimate of true digestibility for alpha-cellulose was 6%. Intestinal transit time decreased from a mean of 37.4 to 28.7 hours with added fiber. Decreased intestinal time would contribute to depression of fry matter digestibility. Increased fecal water output probably also reflected retention by fiber.

Animals↗

Estimation of the potential digestibility and rate of degradation of water-insoluble dietary fiber in the pig cecum with a modified nylon bag technique.

Potential digestibility and rate of degradation of water-insoluble material (WIM) prepared from rutabaga, wheat bran and digesta recovered from the terminal ileum of pigs fed bran- or rutabaga-based diets were measured in the cecum of surgically modified pigs. WIM samples recovered from the cecum after fixed incubation times were analyzed and the rate of total disappearance of organic matter, cellulose, uronic acid and noncellulosic neutral sugars was calculated. Maximum degradation of each WIM occurred within 48 h after incubation and was for rutabaga and its ileal digesta 90 and 70%, respectively, and for bran and bran ileal digesta 55 and 45%, respectively. Cellulose and uronic acid in bran samples did not appear to be degraded, material disappearance being attributable to the loss of noncellulosic neutral sugars. Estimation of potential organic matter digestibility showed rutabaga to be 93%, rutabaga digesta 79%, bran 56% and bran digesta 43% digestible. Fractional rates of digestion in rutabaga samples were significantly faster than in corresponding bran samples. When related to the role of fiber in nutrition the results obtained suggest that cereal fiber would be only slightly modified during gut transit, unlike vegetable fiber in which microbial digestion would probably result in the total destruction of the fiber cell wall matrix.

Animals↗

Digestibility of nitrogen and amino acids in selected protein sources fed to mice.

The purpose of this investigation was 1) to determine the apparent and true digestibilities in mice of nitrogen (N) and amino acids (AA) in commercially refined protein sources, and 2) to estimate metabolic fecal nitrogen (MFN) excretion. Each protein source was fed to adult female mice at 15 and 30% of a purified diet. A protein-free diet was included. Nutrient digestibility was determined by a fecal balance method with chromic oxide as a marker. Apparent digestibility of N in each protein source reflected the dietary N concentration and AA digestibility showed a similar trend. True digestibility (TD) of N was 97-98% for Animal Nutrition Research Council reference protein, casein, gelatin and gliadin, 94-96% for lactalbumin and soy protein and 81% for zein. TD of AA generally reflected TD of N. MFN excretion (g/100 g dry matter consumed) was 0.146 when the protein-free diet was fed and 0.151 by extrapolation to zero N intake. It was concluded that when commercially refined proteins are fed to mice, MFN excretion can be determined by either method, but this may not apply when the protein source contains antinutritive substances.

Amino Acids↗

The protein quality of some enteral products is inferior to that of casein as assessed by rat growth methods and digestibility-corrected amino acid scores.

Protein digestibility and quality of six enteral nutrition products sold in Canada were studied by rat balance and growth methods. Casein+L-methionine, 0.2 g/100 g diet (control) and six enteral products (freeze-dried) were fed as the sole source of protein in diets containing 8.61-9.12 g/100 g protein (N x 6.25) to weanling and 18-mo-old rats for a period of 2 and 1 wk, respectively. A protein-free diet was also included in the feeding studies to permit calculations of true protein digestibility and net protein ratio values. Values for true digestibility of protein as determined in old rats for the control diet and the test products were 95 and 89-93%, respectively. Compared with old rats, protein digestibility values were 5-7 percentage units higher in young rats. The 2-wk relative protein efficiency ratio values (42-56%) or the relative net protein ratio values (61-74%) of the enteral products were considerably lower compared to those of the control (100). Supplementation of an enteral product with cysteine, cysteine + tryptophan, cysteine + threonine or cysteine + tryptophan + threonine caused significant improvement in protein quality; suggesting that the product was limiting in these three amino acids. The protein digestibility-corrected amino acid scores for the enteral products were 43-46, 69-75 and 86-93% by using whole egg, casein and the FAO-WHO (1991) pattern as reference proteins, respectively. The results indicate that these enteral products are inferior to casein in protein quality.

Amino Acids↗

Labeling with 15N as compared with homoarginine suggests a lower prececal digestibility of casein in pigs.

Calculations of prececal protein digestibility based on the stable isotope 15N and the chemical label homoarginine were compared, using casein doubly-labeled with both markers. After food was withheld overnight 24 miniature pigs were given a meal containing 15 g/100 g casein, including 4 g/100 g doubly-labeled protein, and chromic oxide as an indigestible marker. The intestine of eight animals each was removed 3, 6 or 12 h later, divided into 3 sections of equal length, and chyme was collected. Kjeldahl-N, 15N and homoarginine were determined in diet and chyme. Digestibility of casein in the distal third of the small intestine was 93.5 +/- 0.5% and 97.6 +/- 0.3% (P < 0.05) according to 15N and homoarginine label, respectively. Potential causes for this systematic difference were assessed. The data suggest that incorporation of 15N into endogenous proteins and re-entry into the intestinal lumen via secreta and desquamations is the major cause for the 4.2 +/- 0.4% lower digestibility based on the 15N as compared with the homoarginine labeling technique. A preferential occurrence of homoarginine in more easily digestible sections of the protein, faster release during the digestive process and absorption of homoarginine, or incorporation of 15N into proteins of intestinal bacteria are less likely to cause this difference.

Animals↗

The differences in intestinal viscosity produced by barley and beta-glucanase alter digesta enzyme activities and ileal nutrient digestibilities more in broiler chicks than in cocks.

The objectives of this study were to determine whether intestinal viscosity caused by mixed linked barley beta-glucan depresses ileal nutrient digestibility and digestive enzyme activities and to determine the interaction of intestinal viscosity, digestive enzyme activities and ileal nutrient digestibility in different ages of poultry. In Experiments 1 and 2, 1-d-old broiler chicks and 1-y-old cocks, respectively, were fed diets with 60% corn, low and high viscosity barley with or without beta-glucanase, for 3 wk. A 3 x 2 factorial design was used. Comparisons were made only within the same age group. In Experiment 3, 1-d-old broiler chicks were fed high viscosity barley with and without beta-glucanase to measure fecal nutrient and ileal and fecal amino acid digestibility. Broiler chicks fed barley ate less and gained less weight than those fed corn; added beta-glucanase resulted in increases in both food consumption and weight gain for the barley-fed chicks (P < 0.05). Relative pancreas weight was higher (P < 0.05) in chicks fed barley than in those fed corn, and lower with beta-glucanase (P < 0.05). Digesta from barley-fed birds had the highest viscosities, which were decreased (P < 0.05) by beta-glucanase. Amylase and lipase were lower in broiler chicks fed high viscosity barley compared with corn (P < 0.05), and beta-glucanase increased both activities and that of trypsin as well (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

Carbohydrate utilization and digestibility by tilapia, Oreochromis niloticus x O. aureus, are affected by chromic oxide inclusion in the diet.

A 12-wk feeding trial was conducted to study the influence of chromic oxide (Cr2O3) on carbohydrate utilization and digestibility by tilapia, Oreochromis niloticus x O. aureus. Two levels of chromic oxide (0.5 and 2%) were each incorporated into diets containing glucose or starch. Chromic oxide was added at 0 or 8 wk. The diets were fed to triplicate groups of fish weighing 1.11 +/- 0.05 g. Fish fed the starch diet had greater (P < 0.05) weight gain, feed efficiency ratio, protein efficiency ratio, protein deposition and digestibility of protein, lipid, carbohydrate and dry matter than fish fed the glucose diet irrespective of the time and level of chromic oxide supplementation. Fish fed the glucose diet with 0.5% chromic oxide had higher weight gain, feed efficiency ratio, protein efficiency ratio and protein deposition than fish fed the glucose diet with 2% chromic oxide. The ingredient digestibility estimated using 0.5% chromic oxide as the marker was greater than that estimated with 2% chromic oxide. Higher phosphofructokinase and lower glucose-6-phosphatase activity was found in fish fed the starch diet than in fish fed the glucose diet regardless of the time and level of chromic oxide inclusion. Fish fed the glucose diet with 0.5% chromic oxide had higher phosphofructokinase activity and lower tissue chromium concentration than fish fed the glucose diet with 2% chromic oxide irrespective of chromic oxide inclusion time. These data suggest that the level of chromic oxide in the diet alters glucose utilization by tilapia and affects nutrient digestibility by tilapia. The time of chromic oxide inclusion had no effect on carbohydrate utilization and digestibility.

Animal Feed↗

Digestion patterns of endogenous and different exogenous proteins affect the composition of intestinal effluents in humans.

The purpose of this work was to determine if endogenous luminal proteins are stimulated differently by various dietary proteins and if their digestibility differs from that of dietary proteins. Intestinal effluents were collected from the jejunum of four volunteers who had previously fasted or ingested either casein or soybean proteins. After separating the jejunal digested fraction (nonprotein nitrogen) by dialysis, the protein nitrogen fractions of the effluents and of the protein sources were further hydrolyzed in vitro in a digestion cell with simultaneous dialysis of the digestion by-products. The results indicated a higher (P < 0.05) gastrojejunal absorption of casein (64.5 +/- 2.5%) compared with soybean protein (49.9 +/- 4.1%) in humans. Compared with fasting conditions, protein ingestion increased both the total nitrogen and protein nitrogen of the endogenous nitrogen fraction slightly (P < 0.05) but had no effect on the nonprotein nitrogen fraction. The amino acid profiles of the nonprotein nitrogen in the effluents differed from those of both the protein sources and their mixtures with endogenous secretions. This was attributed to the specific release of amino acids by pancreatic enzymes as measured in vitro. The hydrolysis patterns of amino acids were determined by the structure of food proteins and their interaction with endogenous proteins. Soybean and endogenous nitrogen had equivalent digestibilities when measured in vitro.

Adult↗

Dietary carboxymethylcellulose with high instead of low viscosity reduces macronutrient digestion in broiler chickens.

The question addressed was whether the viscosity per se of dietary non-starch polysaccharides influences macronutrient digestion in broiler chickens. Water-soluble carboxymethylcellulose preparations of low (LCMC) or high viscosity (HCMC) were fed to broiler chickens (n = 10/group) from 21 to 35 d of age. The HCMC preparations reduced weight gain and raised water intake compared with LCMC. After the HCMC diet was fed, viscosity of the supernatant of small intestinal contents was significantly raised. The HCMC preparations raised the group mean ATP concentration in the digesta of duodenum plus jejunum, indicating that bacterial activity was increased. Consumption of HCMC depressed apparent fecal digestibility of lipids and nitrogen and also apparent ileal digestibility of starch. The dietary HCMC tended (P = 0.077) to reduce plasma triglyceride concentrations. After HCMC consumption, the weights of the small intestine and colon, without or with contents, were elevated. The data indicate that high viscosity of digesta in broiler chickens is associated with a reduced macronutrient digestion and impaired growth performance. Because the carboxymethylcellulose preparations were nonfermentable by fresh feces, we suggest that HCMC reduces macronutrient digestion by raising the viscosity of small intestinal contents, which is associated with enhanced bacterial fermentation due to accumulation of undigested material.

Animals↗

Dietary fiber decreases the metabolizable energy content and nutrient digestibility of mixed diets fed to humans.

Food labeling regulations implemented by the U.S. Food and Drug Administration emphasize nutrient composition and energy content of foods. Dietary energy and digestibility of complex foods can be affected by the content and type of dietary fiber. The metabolizable energy (ME) content and apparent digestibility of dietary fiber in human diets are difficult to assess. Fiber can affect the digestibility of fat and protein and, subsequently, the ME content of the diet. This study was conducted to measure the ME content of nine diets with different fat and fiber concentrations. Diets varied in level of fat (18, 34 or 47% of energy) and level of total dietary fiber (3, 4 or 7% of diet dry matter) and were consumed for 2 wk. Subjects (n = 17) consumed three diets (14 d for each diet) containing different levels of fiber and one level of fat. Food consumption was measured and all urine and feces were collected during a 5-d period. Combustible energy, protein, fat, total dietary fiber (TDF) and neutral detergent fiber (NDF) were measured in composite samples of food and feces, and urine was analyzed for combustible energy and nitrogen. Metabolizable energy and apparent digestibility coefficients were calculated. Overall, increasing fiber intake decreased fat and protein digestibility. As a consequence of these interactions, the ME content of the diets decreased as fiber intake increased, and TDF and NDF had similar effects on the ME value. A published empirical formula accurately predicted the ME content of diets using either TDF or NDF.

Adult↗

Digestion and absorption rates of [3H]-oleic acid and [14C]-triolein do not differ in rats fed heated (-) and (+) gossypol cottonseed and soybean flours.

This study was conducted to compare in vivo the acute effects of heated (+) and (-) gossypol cottonseed flours with those of soybean flour on lipid digestion and absorption in growing rats. Rats were fed by gastric intubation mixed [3H]-oleic acid and [14C]-triolein with heated flours or without flour (control). Lipid digestion and absorption were determined for 6 h after meal intubation. Both radioactivities recovered in gastrointestinal tract were significantly higher in rats fed (+) gossypol cottonseed flour than in all other groups. The majority of both recovered radioactivities was found in stomach contents, then in stomach wall and finally in intestinal wall. The distribution of both radioactivities at different gastrointestinal levels was similar. In stomach contents and wall, [14C]-radioactivity was primarily in triacylglycerols, but was also recovered in free fatty acids and diacylglycerols. In intestinal wall (mucosa + tunica) [3H]-radioactivity was found at greatest levels in free fatty acids, then in triacylglycerols and diacylglycerols. Greatest [14C]-radioactivity was found in triacylglycerols, then in free fatty acids, in diacylglycerols and last in phospholipids in rats fed the three flours. Therefore no quantitative differences in lipid digestion and absorption were observed among the rats fed the three flours. In conclusion, both cottonseed flours slowed lipid digestion and absorption compared with soybean flour and this delay was greater in the rats fed (+) gossypol cottonseed flour than in those fed (-) gossypol cottonseed flour. However, this inhibiting effect was probably too low to induce physiologically important effects on lipid digestion or absorption.

Animals↗

The protein digestibility-corrected amino acid score.

The protein digestibility-corrected amino acid score (PDCAAS) has been adopted by FAO/WHO as the preferred method for the measurement of the protein value in human nutrition. The method is based on comparison of the concentration of the first limiting essential amino acid in the test protein with the concentration of that amino acid in a reference (scoring) pattern. This scoring pattern is derived from the essential amino acid requirements of the preschool-age child. The chemical score obtained in this way is corrected for true fecal digestibility of the test protein. PDCAAS values higher than 100% are not accepted as such but are truncated to 100%. Although the principle of the PDCAAS method has been widely accepted, critical questions have been raised in the scientific community about a number of issues. These questions relate to 1) the validity of the preschool-age child amino acid requirement values, 2) the validity of correction for fecal instead of ileal digestibility and 3) the truncation of PDCAAS values to 100%. At the time of the adoption of the PDCAAS method, only a few studies had been performed on the amino acid requirements of the preschool-age child, and there is still a need for validation of the scoring pattern. Also, the scoring pattern does not include conditionally indispensable amino acids. These amino acids also contribute to the nutrition value of a protein. There is strong evidence that ileal, and not fecal, digestibility is the right parameter for correction of the amino acid score. The use of fecal digestibility overestimates the nutritional value of a protein, because amino acid nitrogen entering the colon is lost for protein synthesis in the body and is, at least in part, excreted in urine as ammonia. The truncation of PDCAAS values to 100% can be defended only for the limited number of situations in which the protein is to be used as the sole source of protein in the diet. For evaluation of the nutritional significance of proteins as part of mixed diets, the truncated value should not be used. In those cases, a more detailed evaluation of the contribution of the protein to the amino acid composition of the mixed diet is required. From such an evaluation, it appears that milk proteins are superior to plant proteins in cereal-based diets.

Amino Acids↗

Influence of the protein digestion rate on protein turnover in young and elderly subjects.

It has long been recognized that numerous dietary parameters, such as the amount and type of protein and nonprotein energy sources, affect protein metabolism. More recently, we demonstrated that the protein digestion rate is an independent factor regulating postprandial protein gain. Indeed, in young men, using a non-steady-state approach and intrinsically labeled milk protein fractions [whey protein (WP) and casein (CAS)] we showed that a slow digested dietary protein (CAS) induced a greater protein gain than a fast one (WP). The mechanisms of this gain also differed according to the protein rate of digestion. WP stimulated amino acid oxidation and protein synthesis without modifying proteolysis, whereas CAS increased amino acid oxidation and protein synthesis to a lesser extent and strongly inhibited proteolysis. These results led to the concept of "slow" and "fast" protein and were confirmed by further experiments during which the meals tested presented different digestion rates but were otherwise identical in terms of amino acid profile. We also analyzed the effects of fat and carbohydrates added to CAS and WP. Our preliminary results suggest that added nonprotein energy sources to CAS and WP attenuated the differences in both the protein digestion rate and protein gain. Finally, and in contrast to young subjects, a "fast" protein may be more beneficial than a "slow" one in elderly subjects, to limit body protein loss. However, long-term studies are needed to confirm this age-related effect.

Adult↗

Digestion of maize sphingolipids in rats and uptake of sphingadienine by Caco-2 cells.

We investigated the digestion of cerebrosides of plant origin prepared from maize, focusing especially on the digestive fates of trans-4, cis-8- and trans-4, trans-8-sphingadienine, which are common in higher plants. In the small intestinal mucosa and cecal contents of rats, the cerebrosidase activity at pH 5.2 toward the glucosyl linkage in maize cerebrosides (glucosylceramides) was similar to that in cerebrosides of mammalian origin. Similarly, the ceramidase activity toward the amide linkage in ceramides prepared from maize cerebrosides at pH 7.0 was the same as that toward ceramides of mammalian origin. In addition, maize cerebrosides were hydrolyzed to ceramide and free sphingoid bases in the digestive tract of rats after oral administration. To further evaluate the uptake by enterocytes of 4,8-sphingadienine, we used differentiated Caco-2 cells, derived from human colonic carcinoma, as a model of intestinal epithelial cells. The accumulation of sphingoid bases in Caco-2 cells incubated with each isomer of sphingadienine was lower than that after incubation with sphingosine (P < 0.05). Verapamil, a P-glycoprotein inhibitor, increased the accumulation of each sphingadienine but not of sphingosine, suggesting that the efflux of sphingadienine of plant origin, but not sphingosine of mammalian origin, was affected by P-glycoprotein. The digestibility of maize cerebrosides appears similar to that of cerebrosides of mammalian origin, but the metabolic fate of sphingoid bases of plant origin within enterocytes differs from that of sphingosine. Isomers of 4,8-sphingadienine degraded from dietary plant cerebrosides appear to be poorly absorbed from the digestive tract.

Animals↗

Assessment of lutein bioavailability from meals and a supplement using simulated digestion and caco-2 human intestinal cells.

Lutein and zeaxanthin are selectively accumulated in the lens and macular region of the retina. It was suggested that these xanthophylls protect ocular tissues from free-radical damage that can cause cataracts and age-related macular degeneration. Insights regarding the absorption of dietary xanthophylls for delivery to ocular tissues are limited. Our primary objective was to examine factors affecting the transfer of lutein from foods to absorptive intestinal epithelial cells during digestion. Lutein and other carotenoids present in spinach purée and lutein from a commercial supplement were relatively stable during in vitro digestion. Micellarization of lutein and zeaxanthin during the small intestinal phase of digestion exceeded that of beta-carotene and was greater for xanthophylls in oil-based supplements than in spinach. Apical uptake of lutein from micelles by Caco-2 human intestinal cells was linear for at least 8 h, and accumulation from synthetic micelles exceeded that from micelles generated during simulated digestion. Stimulation of chylomicron synthesis resulted in the secretion of 7.6 +/- 0.1% of cellular lutein into the triglyceride-rich fraction in the basolateral chamber. These data support the use of simulated digestion and the Caco-2 cell model as effective tools for identifying factors affecting absorption of dietary carotenoids.

Biological Availability↗