A mixed diet supplemented with L-arabinose does not alter glycaemic or insulinaemic responses in healthy human subjects.

In addition to a yet-to-be published study showing arabinose to have an inhibiting effect on maltase, in vitro studies have shown L-arabinose to exert an inhibiting effect on small-intestinal sucrase and maltase and the consumption of a sucrose-rich drink containing L-arabinose to exert positive effects on postprandial blood glucose, insulin and C-peptide responses in humans. However, the effects of adding L-arabinose to mixed meals on the indices of glucose control are unknown. The purpose of the present study was to investigate whether the positive effects of L-arabinose added to a sugar drink could be reproduced in subjects consuming a mixed meal containing sucrose and/or starch from wheat flour. A total of seventeen healthy men participated in study 1, a randomised, double-blind, cross-over trial. In this study, the subjects consumed two different breakfast meals containing sucrose and starch from wheat flour (meal A) or starch from wheat flour (meal B) supplemented with 0, 5 and 10 % L-arabinose by weight after a 12 h fast. A total of six healthy men participated in study 2, a randomised, double-blind, cross-over trial. In this study, the subjects also consumed meal B served in two different textures and a liquid meal with maltose supplemented with 0 and 20% L-arabinose. In addition, 1·5 g of paracetamol was chosen as an indirect marker to assess gastric emptying. Postprandial plasma glucose, insulin and C-peptide concentrations were measured regularly for 3 h. The results of the present study showed that the peak plasma concentration, time to reach peak plasma concentration or AUC values of glucose, insulin and C-peptide were not altered after consumption of the test meals. Overall, it was not possible to reproduce the beneficial effects of L-arabinose added to sucrose drinks when L-arabinose was mixed in a solid or semi-solid mixed meal.

The effects of L-arabinose on intestinal sucrase activity: dose-response studies in vitro and in humans.

BACKGROUND: On the basis of results in cell cultures, rodents, and pigs, l-arabinose may inhibit intestinal sucrase activity and thereby delay sucrose digestion. OBJECTIVE: The objective was to investigate the dose-response effects of l-arabinose on intestinal sucrase activity in vitro and glucose tolerance, appetite, and energy intake in humans. DESIGN: In vitro, Caco-2 cells were cultured for 21 d, homogenized, and used as an enzyme preparation with sucrose as substrate in concentrations from 7 to 280 mmol/L with 0.84, 1.4, and 2.8 mmol l-arabinose/L as inhibitor. Released glucose was measured after 30 min. In the human studies, 15 healthy men participated in a randomized, double-blind, crossover study. Sucrose beverages (75 g in 300 mL) supplemented with 0%, 1.3%, 2.7%, and 4% by weight of l-arabinose were tested at breakfast. Blood for the measurement of glucose, insulin, C-peptide, incretin hormones, and triacylglycerol was collected under fasting conditions and for 3 h postprandially. Postprandial appetite sensations and energy intake at lunch were registered. RESULTS: In vitro, the addition of l-arabinose resulted in uncompetitive inhibition of sucrase activity. In the human studies, supplementation with 4% l-arabinose produced an 11% lower glucose peak, a 33% lower and delayed insulin peak, a 23% reduction in the incremental area under the curve (iAUC) for insulin, a 23% lower and delayed C-peptide peak, a 9% reduction in the iAUC for C-peptide, a 53% increase in the iAUC for glucagon-like peptide-1 (GLP-1), and a 28% reduction in the iAUC for glucose-dependent insulinotropic polypeptide. No effects on triacylglycerol, gastrointestinal symptoms, appetite ratings, or energy intake were observed. CONCLUSIONS: l-Arabinose inhibits sucrase activity from Caco-2 cells; 4% l-arabinose in sucrose beverages reduces postprandial glucose, insulin, and C-peptide responses and enhances the GLP-1 response in humans without gastrointestinal adverse effects. This trial is registered at clinicaltrials.gov as NCT00302302.

Iron uptake by Caco-2 cells following in vitro digestion: effects of heat treatments of pork meat and pH of the digests.

The present in vitro studies report on iron uptake by Caco-2 cells from pepsin and pepsin+pancreatin-digested pork meat proteins at pH values between 4.6 and 7 mimicking conditions in the duodenum and the proximal jejunum, respectively. Heat treatment of the pork meat resulted in increased iron uptake from pepsin-digested samples to Caco-2 cells at pH 4.6. The major enhancing effects on iron uptake by Caco-2 cells were observed after pepsin digestion in the pH range 4.6-6.0, whereas the pepsin+pancreatin-digested samples resulted in negligible iron uptake in Caco-2 cells at pH 7. Thus, the results emphasize the importance of separating pepsin-digested and pepsin+pancreatin-digested proteins during in vitro studies on iron availability. Furthermore, the present results showed the pH dependency of iron uptake anticipated. The enhancing effect of ascorbic acid was verified by increased iron uptake from pepsin-digested pork meat samples at pH 4.6, while no effect of ascorbic acid was observed at pH 7 in pepsin+pancreatin-digested samples.

Viable, lyophilized lactobacilli do not increase iron absorption from a lactic acid-fermented meal in healthy young women, and no iron absorption occurs in the distal intestine.

Lactic acid-fermented foods have been shown to increase Fe absorption in human subjects, possibly by lowering pH, activation of phytases, production of organic acids, or by the viable lactic acid bacteria. In this study the effect of a heat-inactivated lactic acid-fermented oat gruel with and without added viable, lyophilized Lactobacillus plantarum 299v on non-haem Fe absorption was investigated. Furthermore, Fe absorption in the distal intestine was determined. In a randomized, double-blinded crossover trial eighteen healthy young women aged 22 (SD 3) years with low Fe status (serum ferritin < 30 microg/l) were served the two test gruels, extrinsically labelled with 59Fe and served with two enterocoated capsules (containing 55Fe(II) and 55Fe(III), respectively) designed to disintegrate in the ileum. The meals were consumed on two consecutive days, e.g. in the order AA followed by BB in a second period. Non-haem Fe absorption was determined from 59Fe whole-body retention and isotope activities in blood samples. The concentrations of Fe, lactate, phytate, and polyphenols, and the pH were similar in the heat-inactivated lactic acid-fermented oat gruels with and without added L. plantarum 299v, and no difference in Fe absorption was observed between the test gruels (1.4 and 1.3%, respectively). Furthermore, no absorption of Fe in the distal intestine was observed. In conclusion, addition of viable, lyophilized lactobacillus to a heat-inactivated lactic acid-fermented oat gruel does not affect Fe absorption, and no absorption seems to occur in the distal part of the intestine from low Fe bioavailability meals in these women.

1 -O-alkyl-2-(omega-oxo)acyl-sn-glycerols from shark oil and human milk fat are potential precursors of PAF mimics and GHB.

This study examines the feasibility that peroxidation and lipolysis of 1-O-alkyl-2,3-diacyl-sn-glycerols (DAGE) found in shark liver oil and human milk fat constitutes a potential source of dietary precursors of platelet activating factor (PAF) mimics and of gamma-hydroxybutyrate (GHB). Purified DAGE were converted into 1-O-alkyl-2-acyl-sn-glycerols by pancreatic lipase, without isomerization, and transformed into 1-O-alkyl-2-oxoacyl-sn-glycerols by mild autooxidation. The various core aldehydes without derivatization, as well as the corresponding dinitrophenylhydrazones, were characterized by chromatographic retention time and diagnostic ions by online electrospray mass spectrometry. Core aldehydes of oxidized shark liver oil yielded 23 molecular species of 1-O-alkyl-sn-glycerols with short-chain sn-2 oxoacyl groups, ranging from 4 to 13 carbons, some unsaturated. Autooxidation of human milk fat yielded 1-O-octadecyl-2-(9-oxo)nonanoyl-sn-glycerol, as the major core aldehyde. Because diradylglycerols with short fatty chains are absorbed in the intestine and react with cytidine diphosphate-choline in the enterocytes, it is concluded that formation of such PAF mimics as 1-O-alkyl-2-(omega-oxo)acyl-sn-glycerophosphocholine from unsaturated dietary DAGE is a realistic possibility. Likewise, a C4 core alcohol produced by aldol-keto reduction of a C4 core aldehyde constitutes a dietary precursor of the neuromodulator and recreational drug GHB, which has not been previously pointed out.

A lactic acid-fermented oat gruel increases non-haem iron absorption from a phytate-rich meal in healthy women of childbearing age.

Lactic acid-fermented foods have been shown to increase Fe absorption in human subjects, possibly by lowering pH, activation of phytases, and formation of soluble complexes of Fe and organic acids. We tested the effect of an oat gruel fermented with Lactobacillus plantarum 299v on non-haem Fe absorption from a low-Fe bioavailability meal compared with a pasteurised, fermented oat gruel and non-fermented oat gruels. In a cross-over trial twenty-four healthy women with a mean age of 25 (sd 4) years were served (A) fermented gruel, (B) pasteurised fermented gruel, (C) pH-adjusted non-fermented gruel, and (D) non-fermented gruel with added organic acids. The meals were extrinsically labelled with 55Fe or 59Fe and consumed on 4 consecutive days, for example, in the order ABBA or BAAB followed by CDDC or DCCD in a second period. Fe absorption was determined from isotope activities in blood samples. The fermented gruel with live L. plantarum 299v increased Fe absorption significantly (P < 0.0001) compared with the pasteurised and non-fermented gruels. The lactic acid concentration in the fermented gruel was 19 % higher than in the pasteurised gruel, but the Fe absorption was increased by 50 %. In the gruel with organic acids, the lactic acid concentration was 52 % lower than in the pasteurised gruel, with no difference in Fe absorption. The fermented gruel increased non-haem Fe absorption from a phytate-rich meal in young women, indicating a specific effect of live L. plantarum 299v and not only an effect of the organic acids.

The usefulness of in vitro models to predict the bioavailability of iron and zinc: a consensus statement from the HarvestPlus expert consultation.

A combination of dietary and host-related factors determines iron and zinc absorption, and several in vitro methods have been developed as preliminary screening tools for assessing bioavailability. An expert committee has reviewed evidence for their usefulness and reached a consensus. Dialyzability (with and without simulated digestion) gives some useful information but cannot predict the correct magnitude of response and may sometimes predict the wrong direction of response. Caco-2 cell systems (with and without simulated digestion) have been developed for iron availability, but the magnitude of different effects does not always agree with results obtained in human volunteers, and the data for zinc are too limited to draw conclusions about the validity of the method. Caco-2 methodologies vary significantly between laboratories and require experienced technicians and good quality cell culture facilities to obtain reproducible results. Algorithms can provide semi-quantitative information enabling diets to be classified as high, moderate, or low bioavailability. While in vitro methods can be used to generate ideas and develop hypotheses, they cannot be used alone for important decisions concerning food fortification policy, selection of varieties for plant breeding programs, or for new product development in the food industry. Ultimately human studies are required for such determinations.

Calcium from milk or calcium-fortified foods does not inhibit nonheme-iron absorption from a whole diet consumed over a 4-d period.

BACKGROUND: Single-meal studies have indicated that calcium inhibits iron absorption in humans. However, numerous dietary factors influence iron absorption, and the effect of calcium may not be as pronounced when calcium is served as part of a whole diet. OBJECTIVE: We investigated the effect of 3 sources of calcium served with the 3 main meals on nonheme-iron absorption from a 4-d diet. DESIGN: (59)Fe absorption was estimated from whole-body retention measurements in 14 women aged 21-34 y, each of whom consumed four 4-d diets in a randomized crossover design. The diets differed in the source of calcium as follows: a basic diet (BD) with a low content of calcium (224 mg Ca/d), a BD with a glass of milk served at each meal (826 mg Ca/d), a BD with calcium lactate (802 mg Ca/d), and a BD with a milk mineral isolate containing calcium (801 mg Ca/d). The 2 latter calcium sources were added to selected foods of the BD (rye bread, white bread, chocolate cake, and orange juice), and these foods were consumed with the 3 meals. All diets provided 13.2 mg Fe/d. RESULTS: No significant differences in nonheme-iron absorption were found between the BD and the BD supplemented with milk, calcium lactate, or the milk mineral isolate [7.4% (95% CI: 5.3%, 10.5%), 5.2% (3.5%, 7.9%), 6.7% (5.0%, 8.9%), and 5.1% (3.2%, 7.9%), respectively; P = 0.34]. CONCLUSION: Consumption of a glass of milk with the 3 main meals or of an equivalent amount of calcium from fortified foods does not decrease nonheme-iron absorption from a 4-d diet.

Feeding minipigs fish oil for four weeks lowers postprandial triacylglycerolemia.

We wanted to establish a minipig model for the study of postprandial lipemia and plasma lipid clearance after fish oil consumption. Seven minipigs were fed a fish oil-enriched nonpurified diet and a control diet for 4 wk in a randomized cross-over study. After each intervention period, each pig was challenged with a gastric fat load (2 g fat/kg body) and an intravenous fat bolus (0.1 g/kg body) on separate days. Frequent blood samples were collected for 6 h after the gastric fat load and for 40 min after the intravenous bolus. The fish oil-enriched diet was associated with lower triacylglycerol, glycerol and nonesterified fatty acid concentrations in the hours after the gastric fat load than the control diet (P < 0.05). In contrast, the triacylglycerol disappearance rate after the intravenous fat bolus was not affected by fish oil (P = 0.19). In conclusion, dietary fish oil supplementation attenuates postprandial lipemia in minipigs similarly to what occurs in humans. Minipigs could serve as a useful model for future studies of this phenomenon. We observed no significant effect of fish oil supplementation on plasma triacylglycerol clearance and thus were unable to identify the mechanism explaining the attenuated lipemia in minipigs.

Oxidant-stimulated chloride secretion in rat jejunum in vitro is mediated by eicosanoids.

Specific effects of the cytotoxic secondary lipid oxidation product, 4-hydroxynonenal (10(-8)-10(-4) M), on intact sheets of rat jejunum were measured as changes in short circuit current (delta(I)sc) following cumulative addition to either the mucosal or serosal side, using the analogous aldehyde, nonenal, as reference. 4-Hydroxynonenal stimulated I(sc) from the serosal side (maximal delta(I)sc = 27.2 +/- 3.5 microA/cm2, mean +/- SEM, N = 32) while nonenal stimulated I(sc) primarily from the mucosal side (maximal delta(I)sc = 16.2 +/- 3.4 microA/cm2, N = 20). Inhibition by 100 microM bumetanide (4-hydroxynonenal: 88.9 +/- 3.0%, N = 6, p < 0.05, nonenal: 69.3 +/- 2.9%, N = 6, P < 0.05) indicated chloride secretion. Nonenal-induced delta(I)sc was inhibited (72.5 +/- 1.2%, N = 8, P < 0.05) by a combination of nordihydroguaiaretic acid (100 microM) and piroxicam (10 microM), while 4-hydroxynonenal-induced delta(I)sc, was abolished by piroxicam (N = 8, P < 0.001) and inhibited by 1 microM tetrodotoxin (69.8 +/- 9.7%, N = 6, P < 0.001). These data indicate that 4-hydroxynonenal stimulates chloride secretion mediated by prostaglandins and the enteric nervous system. The site of action (serosal) being opposite to the reference aldehyde.

Increasing the cooking temperature of meat does not affect nonheme iron absorption from a phytate-rich meal in women.

The effect of increasing cooking temperatures of meat on nonheme iron absorption from a composite meal was investigated. Cysteine-containing peptides may have a role in the iron absorption enhancing effect of muscle proteins. Heat treatment can change the content of sulfhydryl groups produced from cysteine and thereby affect iron absorption. Twenty-one women (25 +/- 3 y) were served a basic meal without meat and two other meals consisting of the basic meal plus 75 g of pork meat cooked at 70, 95 or 120 degrees C. The meals were extrinsically labeled with (55)Fe or (59)Fe. Iron absorption was determined from measurements of whole-body (59)Fe retention and the activity of (55)Fe and (59)Fe in blood samples. Nonheme iron absorptions were 0.9 (0.5-4.0)% (P = 0.06), 0.7 (0.4-3.9)% (P = 0.1) and 2.0 (1.3-3.1)% (P < 0.001) greater when meat cooked at 70, 95 or 120 degrees C, respectively, was added to the basic meal. Increasing the cooking temperature of meat did not impair nonheme iron absorption compared with cooking at 70 degrees C. Because the cysteine content of meat decreased with increasing cooking temperature, this argues against a specific contribution of sulfhydryl groups from cysteine residues in the promotion of nonheme iron absorption by meat proteins.

Nonheme-iron absorption from a phytate-rich meal is increased by the addition of small amounts of pork meat.

BACKGROUND: Muscle tissue from various sources is known to promote nonheme-iron absorption. However, systematic studies of the dose dependency of this effect of meat on iron absorption from an inhibitory meal with low amounts of meat are lacking. OBJECTIVE: We investigated the dose-response effect of small amounts of meat on nonheme-iron absorption from a meal presumed to have low iron bioavailability. DESIGN: Forty-five healthy women with a mean (+/-SD) age of 24 +/- 3 y were randomly assigned to 1 of 3 groups, each of which was served (A) a basic meal (rice, tomato sauce, pea purée, and a wheat roll) and (B) the basic meal with either 25, 50, or 75 g pork (longissimus muscle). Meal A contained 2.3 mg nonheme iron, 7.4 mg vitamin C, and 220 mg (358 micro mol) phytate. Each meal was served twice, and the order of the meals was ABBA or BAAB. The meals were extrinsically labeled with (55)Fe or (59)Fe. Iron absorption was determined from measurements of (59)Fe whole-body retention and the activity of (55)Fe and (59)Fe in blood samples. RESULTS: Twenty-five grams meat did not increase nonheme-iron absorption significantly (P = 0.13), whereas absorption increased 44% (P < 0.001) and 57% (P < 0.001), respectively, when 50 and 75 g meat were added to the basic meal. In absolute values, this corresponds to an absorption that was 2.6% and 3.4% higher, respectively, than that with the basic meal after adjustment of the data to a level of 40% absorption from a reference dose. CONCLUSION: Small amounts of meat (>or=50 g) significantly increase nonheme-iron absorption from a phytate-rich meal low in vitamin C.