Relative abundance of the Prevotella genus within the human gut microbiota of elderly volunteers determines the inter-individual responses to dietary supplementation with wheat bran arabinoxylan-oligosaccharides

BACKGROUND

The human colon is colonised by a dense microbial community whose species composition and metabolism are linked to health and disease. The main energy sources for colonic bacteria are dietary polysaccharides and oligosaccharides. These play a major role in modulating gut microbial composition and metabolism, which in turn can impact on health outcomes.

RESULTS

We investigated the influence of wheat bran arabinoxylan oligosaccharides (AXOS) and maltodextrin supplements in modulating the composition of the colonic microbiota and metabolites in healthy adults over the age of 60. Male and female volunteers, (n = 21, mean BMI 25.2 ± 0.7 kg/m2) participated in the double-blind, cross over supplement study. Faecal samples were collected for analysis of microbiota, short chain fatty acids levels and calprotectin. Blood samples were collected to measure glucose, cholesterol and triglycerides levels. There was no change in these markers nor in calprotectin levels in response to the supplements. Both supplements were well-tolerated by the volunteers. Microbiota analysis across the whole volunteer cohort revealed a significant increase in the proportional abundance of faecal Bifidobacterium species (P ≤ 0.01) in response to AXOS, but not maltodextrin, supplementation. There was considerable inter-individual variation in the other bacterial taxa that responded, with a clear stratification of volunteers as either Prevotella-plus (n = 8; > 0.1% proportional abundance) or Prevotella-minus (n = 13; ≤0.1% proportional abundance) subjects founded on baseline sample profiles. There was a significant increase in the proportional abundance of both faecal Bifidobacterium (P ≤ 0.01) and Prevotella species (P ≤ 0.01) in Prevotella-plus volunteers during AXOS supplementation, while Prevotella and Bacteroides relative abundances showed an inverse relationship. Proportional abundance of 26 OTUs, including bifidobacteria and Anaerostipes hadrus, differed significantly between baseline samples of Prevotella-plus compared to Prevotella-minus individuals.

CONCLUSIONS

The wheat bran AXOS supplementation was bifidogenic and resulted in changes in human gut microbiota composition that depended on the initial microbiota profile, specifically the presence or absence of Prevotella spp. as a major component of the microbiota. Our data therefore suggest that initial profiling of individuals through gut microbiota analysis should be considered important when contemplating nutritional interventions that rely on prebiotics.

TRIAL REGISTRATION

Clinical trial registration number: NCT02693782 . Registered 29 February 2016 - Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT02693782?term=NCT02693782&rank=1.

Nondigestible Carbohydrates Affect Metabolic Health and Gut Microbiota in Overweight Adults after Weight Loss

BACKGROUND

The composition of diets consumed following weight loss (WL) can have a significant impact on satiety and metabolic health.

OBJECTIVE

This study was designed to test the effects of including a nondigestible carbohydrate to achieve weight maintenance (WM) following a period of WL.

METHODS

Nineteen volunteers [11 females and 8 males, aged 20-62 y; BMI (kg/m2): 27-42] consumed a 3-d maintenance diet (15%:30%:55%), followed by a 21-d WL diet (WL; 30%:30%:40%), followed by 2 randomized 10-d WM diets (20%:30%:50% of energy from protein:fat:carbohydrate) containing either resistant starch type 3 (RS-WM; 22 or 26 g/d for females and males, respectively) or no RS (C-WM) in a within-subject crossover design without washout periods. The primary outcome, WM after WL, was analyzed by body weight. Secondary outcomes of fecal microbiota composition and microbial metabolite concentrations and gut hormones were analyzed in fecal samples and blood plasma, respectively. All outcomes were assessed at the end of each dietary period.

RESULTS

Body weight was similar after the RS-WM and C-WM diets (90.7 and 90.8 kg, respectively), with no difference in subjectively rated appetite. During the WL diet period plasma ghrelin increased by 36% (P < 0.001), glucose-dependent insulinotropic polypeptide (GIP) decreased by 33% (P < 0.001), and insulin decreased by 46% (P < 0.001), but no significant differences were observed during the RS-WM and C-WM diet periods. Fasting blood glucose was lower after the RS-WM diet (5.59 ± 0.31 mmol/L) than after the C-WM diet [5.75 ± 0.49 mmol/L; P = 0.015; standard error of the difference between the means (SED): 0.09]. Dietary treatments influenced the fecal microbiota composition (R2 = 0.054, P = 0.031) but not diversity.

CONCLUSIONS

The metabolic benefits, for overweight adults, from WL were maintained through a subsequent WM diet with higher total carbohydrate intake. Inclusion of resistant starch in the WM diet altered gut microbiota composition positively and resulted in lower fasting glucose compared with the control, with no apparent change in appetite. This trial was registered at clinicaltrials.gov as NCT01724411.

Stevia Beverage Consumption prior to Lunch Reduces Appetite and Total Energy Intake without Affecting Glycemia or Attentional Bias to Food Cues: A Double-Blind Randomized Controlled Trial in Healthy Adults

BACKGROUND

Stevia is a zero-calorie alternative to caloric sugars. Substituting caloric sweeteners with noncaloric sweeteners reduces available energy, but their effects on appetite, subsequent food intake, and neurocognitive responses are still unclear.

OBJECTIVE

The aim was to examine whether sweetness with or without calories influences food intake, appetite, blood glucose concentrations, and attentional bias (AB) to food cues.

METHODS

This was a randomized, controlled, double-blind crossover study. Healthy participants [n = 20; aged 27 ± 5 y,  55% female; BMI (kg/m2): 21.8 ± 1.5] completed 5 visits, consuming 5 study beverages: 330 mL water (control, no sweet taste, no calories) and either 330 mL water containing 40 g glucose or sucrose (sweet taste; calories, both 160 kcal), maltodextrin (no sweet taste; calories, 160 kcal), or 240 ppm stevia (sweet taste, no calories). Glucose and stevia beverages were matched for sweetness. Subjective appetite ratings and blood glucose were measured at baseline and at 15, 30, and 60 min postprandially. At 15 min participants performed a visual-dot probe task to assess AB to food cues; at 30 min, participants were offered an ad libitum lunch; food intake was measured.

RESULTS

Subjective appetite ratings showed that preload sweetness and calorie content both affected appetite. The total AUC for glycemia was significantly higher after the caloric beverages (mean ± SD: maltodextrin, 441 ± 57.6;  glucose, 462 ± 68.1;  sucrose, 425 ± 53.6 mmol × min × L-1 ) compared with both stevia (320 ± 34.2 mmol × min × L-1) and water (304 ± 32.0 mmol × min × L-1) (all P < 0.001). Total energy intake (beverage and meal) was significantly lower after the stevia beverage (727 ± 239 kcal) compared with water (832 ± 198 kcal,  P = 0.013), with no significant difference between the water and caloric beverages (P = 1.00 for water vs. maltodextrin, glucose, and sucrose). However, food-related AB did not differ across conditions (P = 0.140).

CONCLUSIONS

This study found a beneficial and specific effect of a stevia beverage consumed prior to a meal on appetite and energy intake in healthy adults. This trial is registered at clinicaltrials.gov as NCT03711084.

Impact of carbohydrate substrate complexity on the diversity of the human colonic microbiota

The diversity of the colonic microbial community has been linked with health in adults and diet composition is one possible determinant of diversity. We used carefully controlled conditions in vitro to determine how the complexity and multiplicity of growth substrates influence species diversity of the human colonic microbiota. In each experiment, five parallel anaerobic fermenters that received identical faecal inocula were supplied continuously with single carbohydrates (either arabinoxylan-oligosaccharides (AXOS), pectin or inulin) or with a '3-mix' of all three carbohydrates, or with a '6-mix' that additionally contained resistant starch, β-glucan and galactomannan as energy sources. Inulin supported less microbial diversity over the first 6 d than the other two single substrates or the 3- and 6-mixes, showing that substrate complexity is key to influencing microbiota diversity. The communities enriched in these fermenters did not differ greatly at the phylum and family level, but were markedly different at the species level. Certain species were promoted by single substrates, whilst others (such as Bacteroides ovatus, LEfSe P = 0.001) showed significantly greater success with the mixed substrate. The complex polysaccharides such as pectin and arabinoxylan-oligosaccharides promoted greater diversity than simple homopolymers, such as inulin. These findings suggest that dietary strategies intended to achieve health benefits by increasing gut microbiota diversity should employ complex non-digestible substrates and substrate mixtures.

Impact of polyols on Oral microbiome of Estonian schoolchildren

BACKGROUND

Oral microbiome has significant impact on both oral and general health. Polyols have been promoted as sugar substitutes in prevention of oral diseases. We aimed to reveal the effect of candies containing erythritol, xylitol or control (sorbitol) on salivary microbiome.

METHODS

Ninety children (11.3 ± 0.6 years) consumed candies during 3 years. Microbial communities were profiled using Illumina HiSeq 2000 sequencing and real-time PCR.

RESULTS

The dominant phyla in saliva were Firmicutes (39.1%), Proteobacteria (26.1%), Bacteroidetes (14.7%), Actinobacteria (12%) and Fusobacteria (6%). The microbiome of erythritol group significantly differed from that of the other groups. Both erythritol and xylitol reduced the number of observed bacterial phylotypes in comparison to the control group. The relative abundance of the genera Veillonella, Streptococcus and Fusobacterium were higher while that of Bergeyella lower after erythritol intervention when comparing with control. The lowest prevalence of caries-related mutans streptococci corresponded with the lowest clinical caries markers in the erythritol group.

CONCLUSIONS

Daily consumption of erythritol, xylitol or control candies has a specific influence on the salivary microbiome composition in schoolchildren. Erythritol is associated with the lowest prevalence of caries-related mutans streptococci and the lowest levels of clinical caries experience.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier NCT01062633.

Nutritional interest of dietary fiber and prebiotics in obesity: Lessons from the MyNewGut consortium

The aim of EU project MyNewGut is to contribute to future public health-related recommendations supported by new insight in gut microbiome and nutrition-host relationship. In this Opinion Paper, we first revisit the concept of dietary fiber, taking into account their interaction with the gut microbiota. This paper also summarizes the main effects of dietary fibers with prebiotic properties in intervention studies in humans, with a particular emphasis on the effects of arabinoxylans and arabinoxylo-oligosaccharides on metabolic alterations associated with obesity. Based on the existing state of the art and future development, we elaborate the steps required to propose dietary guidelines related to dietary fibers, taking into account their interaction with the gut microbiota.

Modulation of the human gut microbiota by dietary fibres occurs at the species level

Background

Dietary intake of specific non-digestible carbohydrates (including prebiotics) is increasingly seen as a highly effective approach for manipulating the composition and activities of the human gut microbiota to benefit health. Nevertheless, surprisingly little is known about the global response of the microbial community to particular carbohydrates. Recent in vivo dietary studies have demonstrated that the species composition of the human faecal microbiota is influenced by dietary intake. There is now potential to gain insights into the mechanisms involved by using in vitro systems that produce highly controlled conditions of pH and substrate supply.

Results

We supplied two alternative non-digestible polysaccharides as energy sources to three different human gut microbial communities in anaerobic, pH-controlled continuous-flow fermentors. Community analysis showed that supply of apple pectin or inulin resulted in the highly specific enrichment of particular bacterial operational taxonomic units (OTUs; based on 16S rRNA gene sequences). Of the eight most abundant Bacteroides OTUs detected, two were promoted specifically by inulin and six by pectin. Among the Firmicutes, Eubacterium eligens in particular was strongly promoted by pectin, while several species were stimulated by inulin. Responses were influenced by pH, which was stepped up, and down, between 5.5, 6.0, 6.4 and 6.9 in parallel vessels within each experiment. In particular, several experiments involving downshifts to pH 5.5 resulted in Faecalibacterium prausnitzii replacing Bacteroides spp. as the dominant sequences observed. Community diversity was greater in the pectin-fed than in the inulin-fed fermentors, presumably reflecting the differing complexity of the two substrates.

Conclusions

We have shown that particular non-digestible dietary carbohydrates have enormous potential for modifying the gut microbiota, but these modifications occur at the level of individual strains and species and are not easily predicted a priori. Furthermore, the gut environment, especially pH, plays a key role in determining the outcome of interspecies competition. This makes it crucial to put greater effort into identifying the range of bacteria that may be stimulated by a given prebiotic approach. Both for reasons of efficacy and of safety, the development of prebiotics intended to benefit human health has to take account of the highly individual species profiles that may result.

Electronic supplementary material

The online version of this article (doi:10.1186/s12915-015-0224-3) contains supplementary material, which is available to authorized users.

Development and Validation of an in vitro Experimental GastroIntestinal Dialysis Model with Colon Phase to Study the Availability and Colonic Metabolisation of Polyphenolic Compounds

The biological effects of polyphenols depend on their mechanism of action in the body. This is affected by bioconversion by colon microbiota and absorption of colonic metabolites. We developed and validated an in vitro continuous flow dialysis model with colon phase (GastroIntestinal dialysis model with colon phase) to study the gastrointestinal metabolism and absorption of phenolic food constituents. Chlorogenic acid was used as model compound. The physiological conditions during gastrointestinal digestion were mimicked. A continuous flow dialysis system simulated the one-way absorption by passive diffusion from lumen to mucosa. The colon phase was developed using pooled faecal suspensions. Several methodological aspects including implementation of an anaerobic environment, adapted Wilkins Chalgren broth medium, 1.10(8) CFU/mL bacteria suspension as inoculum, pH adaptation to 5.8 and implementation of the dialysis system were conducted. Validation of the GastroIntestinal dialysis model with colon phase system showed a good recovery and precision (CV < 16 %). Availability of chlorogenic acid in the small intestinal phase (37 ± 3 %) of the GastroIntestinal dialysis model with colon phase is comparable with in vivo studies on ileostomy patients. In the colon phase, the human faecal microbiota deconjugated chlorogenic acid to caffeic acid, 3,4-dihydroxyphenyl propionic acid, 4-hydroxybenzoic acid, 3- or 4-hydroxyphenyl acetic acid, 2-methoxy-4-methylphenol and 3-phenylpropionic acid. The GastroIntestinal dialysis model with colon phase is a new, reliable gastrointestinal simulation system. It permits a fast and easy way to predict the availability of complex secondary metabolites, and to detect metabolites in an early stage after digestion. Isolation and identification of these metabolites may be used as references for in vivo bioavailability experiments and for investigating their bioactivity in in vitro experiments.

Effects of erythritol on endothelial function in patients with type 2 diabetes mellitus: a pilot study

Sugar substitutes are important in the dietary management of diabetes mellitus. Erythritol is a non-caloric dietary bulk sweetener that reverses endothelial dysfunction in diabetic rats. We completed a pilot study to examine the effects of erythritol on vascular function in patients with type 2 diabetes mellitus. Participants (n = 24) consumed erythritol 36 g/day as an orange-flavored beverage for 4 weeks and a single dose of 24 g during the baseline and final visits. We assessed vascular function before and after acute (2 h) and chronic (4 weeks) erythritol consumption. Acute erythritol improved endothelial function measured by fingertip peripheral arterial tonometry (0.52 ± 0.48 to 0.87 ± 0.29 au, P = 0.005). Chronic erythritol decreased central pulse pressure (47 ± 13 to 41 ± 9 mmHg, P = 0.02) and tended to decrease carotid-femoral pulse wave velocity (P = 0.06). Thus, erythritol consumption acutely improved small vessel endothelial function, and chronic treatment reduced central aortic stiffness. Erythritol may be a preferred sugar substitute for patients with diabetes mellitus.

Abstract 359: Effects of Erythritol on Endothelial Function in People with Type 2 Diabetes Mellitus

Erythritol is a polyol compound used as a low calorie nutritive sweetener. Several animal model studies have shown that erythritol has antioxidant properties and may improve endothelial function. The goal of this pilot study was to obtain evidence for such an effect in patients with type 2 diabetes mellitus (DM). Vascular testing included brachial artery flow-mediated dilation (FMD), reactive hyperemia, digital peripheral arterial tonometry (EndoPAT), carotid-femoral pulse wave velocity (PWV), central pulse pressure, and brachial blood pressure. We also measured blood glucose, insulin, C-peptide, C-reactive protein and urine F2 isoprostanes. Twenty-four participants (age 56±5 yrs, 54% female) consumed erythritol as a flavored beverage (12g x3/day) for 28 days. We assessed the effect of erythritol on vascular function compared to baseline at three time points: Acute (2 hours after erythritol 24 g), chronic (at day 28), and acute-on-chronic (day 28 after erythritol 24g). We did not observe a significant change in brachial artery FMD or reactive hyperemia. Acute consumption of erythritol produced a significant improvement in endothelial function measured by EndoPAT (lnPAT ratio 0.52±0.48 vs. 0.87±0.29, P=0.005). lnPAT ratio was 0.72±0.33 (P=0.19 vs. baseline) after chronic consumption and 0.84±0.34 after acute-on-chronic consumption (P=0.02). Following 28 days of erythritol consumption we observed a favorable effect on markers of aortic compliance: significant reduction in central pulse pressure from 47±13 to 41±9 mmHg (P=0.021) and strong trend for decreased PWV from 9.1±1.4 to 8.6±1.6 cm/sec (P=0.06). Markers of glucose metabolism, oxidative stress and inflammation did not vary throughout the study. We observed a trend for reduced systolic blood pressure after chronic erythritol consumption (131±16 to 128±11 mmHg, P=0.10). A subgroup analysis of 12 patients with systolic blood pressure above 130 mmHg yield a significant reduction in systolic blood pressure from 144±12 to 133±9 mmHg (P=0.01). This pilot study suggests that erythritol may have favorable effects on small vessel endothelial function, blood pressure, and central aortic stiffness in DM patients. Confirmation of these findings will require a placebo-controlled study.

Food-based strategies to modulate the composition of the intestinal microbiota and their associated health effects

The most well known food-based strategies to modulate the composition of the intestinal microbiota are the dietary use of prebiotics, probiotics and their combination, synbiotics. Currently established prebiotic compounds are mainly targeting the bifidobacteria population of the colon microbiota. A good illustration of the importance of high colonic bifidobacteria levels is the observation that breast milk creates an environment in the colon (because of its high amount in galacto-oligosaccharides with prebiotic activity) favouring the development of a simple flora, dominated by bifidobacteria to which various health benefits have been ascribed. Currently, high colonic bifidobacteria levels has been considered favourably at all ages and strategies to augment their presence have been demonstrated in placebo-controlled intervention studies; e.g. in toddlers to reduce sickness events, in adults to reduce the risk for developing gastrointestinal diseases and in the elderly to re-enhance their declining immune activity. The intestinal microbiota can be considered as a metabolically adaptable and rapidly renewable organ of the body. However, unbalances in its microbial community and activities are found to be implicated in disease initiation and progression, such as chronic inflammatory bowel diseases and colonic cancers. Restoration of this balance by increasing bifidobacteria levels has demonstrated to reduce disease severity of patients and to improve well-being in healtly volunteers. New emerging evidence on the difference in the composition of the colonic microbiota between obese and lean volunteers has opened new areas for pre-, pro- and synbiotic research. Additionally, as knowledge will increase about the microbial bio-conversion of polyphenolic compounds into bioactive metabolites in the colon and whether food-based strategies can augment such bioconversion into more potent compounds with anti-oxidant and/or anti-inflammatory activity new areas of research will be discovered. This paper provides an up-to-date review of the health benefits associated to the induction of high bifidobacteria levels in the colon by the use of prebiotics (inulin and oligofructose). New areas of emerging science will be discussed as well.

Do thickening properties of locust bean gum affect the amount of calcium, iron and zinc available for absorption from infant formula? In vitro studies

Locust bean gum acts as a milk thickener in infant formula because of its high apparent viscosity. The effects of such thickening agents on metabolic and physiologic responses during infancy have not been clarified sufficiently. Due to the increased volume of the digest and the bulking and trapping effects, digestion and absorption of nutrients may be influenced in presence of locust bean gum. The central question addressed in this paper is whether the thickening properties of locust bean gum affect the availability of calcium, iron, and zinc. Increasing amounts of powdered locust bean gum were homogenised with infant formula and samples were diluted to 0.14, 0.27, 0.42 and 0.71 g/100 ml. Viscosity of the samples was measured by a Carrie-Med CSL100 rheometer. Available amounts of calcium, iron, and zinc were evaluated using a continuous-flow dialysis model with preliminary digestion. Elemental contents of samples and dialysates were analysed with atomic absorption spectrometry. The first set of experiments showed that addition of locust bean gum to infant formulas increased the viscosity of the luminal contents. Correlations between the locust bean gum concentration and the viscosity of the samples before and after gastric or intestinal digestion were highly significant (0.97). In the second set of experiments, the correlations between the locust bean gum concentration and the amounts of calcium trapped by the locust bean gum fraction also showed high significance (0.93). In the third experimental design, again strong correlations were found between the viscosity of the intestinal digest and the amounts of calcium trapped by the fibre fraction (0.90). For iron and zinc, no such relationships were found. From this experimental set-up it appears that locust bean gum influences calcium availability in infant formulas by means of its physical properties to act as thickening agent, rather than its chemical ability to form complexes as demonstrated earlier with respect to iron and zinc.

Availabilities of calcium, iron, and zinc from dairy infant formulas is affected by soluble dietary fibers and modified starch fractions

OBJECTIVE

Insoluble dietary fiber is a known inhibitor of mineral absorption, whereas the effects of soluble dietary fibers (including prebiotics) are less known. The aim was to study calcium, iron, and zinc availabilities from dairy infant formulas supplemented with soluble dietary fibers and modified starches in vitro.

METHODS

Dairy infant formulas were supplemented with soluble dietary fibers (3%, dry wt) and modified starches (16% pregelatinized rice starch and 1.9% maltodextrin, dry wt) and kept in a well-controlled and defined environment in vitro. Pooled mature human milk was used as the reference standard.

RESULTS

Calcium availability from standard formula was elevated by 30% after inulin supplementation (17.2%), whereas locust bean gum (11.9%) and high esterified pectin (11.7%) reduced availability by approximately 10%. Iron availability from standard formula was increased by pregelatinized rice starch (3.8%), whereas availability was reduced in the following order: high esterified pectin (2.3%), oligofructose (2.2%), and low esterified pectin (2.1%). Zinc availability was highest after the addition of pregelatinized rice starch (13.5%) but lowest with the addition of locust bean gum (6.8%) and maltodextrin (5.4%).

CONCLUSIONS

This study showed that addition of soluble dietary fiber affects calcium, iron, and zinc availabilities in positive (inulin) and negative ways, depending on the type of the dietary fiber used.

Calcium, iron and zinc availability from weaning meals

During the weaning period, solid foods are introduced in the diet to complement human milk or infant formula. Consequently, marginal deficiencies may easily develop because of inappropriate feeding and low bioavailability of nutrients. The objective of this study was to determine calcium, iron and zinc availability from weaning foods that contained a variety of ingredients but almost the same dietary fibre content, and to describe dietary factors that influence availability in a linear matter. Availability measurements from eight meals were made in vitro by a continuous-flow dialysis system with preliminary intraluminal digestion. Calcium, iron and zinc were analysed by flame atomic absorption spectrometry; ascorbic acid content was taken from food-composition tables; and macronutrient and mineral contents were obtained from the manufacturer. Calcium availability was higher in fruits (mean +/- SD, 39.2 +/- 4.1%) than vegetables (31.7 +/- 5.8%) (p < or = 0.001). Iron availability was marginally significant higher in vegetables (13.0 +/- 4.7%) than fruits (10.2 +/- 1.6%) (p = 0.027). Zinc availability showed higher availability in fruits (52.3 +/- 22.3%) than vegetables (22.1 +/- 5.6%) (p < or = 0.001).

CONCLUSION

A major portion (47.8%) of the variance in calcium availability, as determined by multiple regression, could be explained by protein (p = 0.058, beta = -0.691). Major predictors of iron availability among the nutrients were iron content of the meal (p = 0.014, beta = -0.838), carbohydrates (p = 0.044, beta = -0.610) and dietary fibre (p = 0.235, beta = -0.285). Zinc availability was merely influenced by the protein (p = 0.010, beta = -0.876) and fat content of the meals (p = 0.295, beta = 0.255) in relation to other nutrients.

In vitro availability of zinc from infant foods with increasing phytic acid contents

An in vitro method was used to determine the availability of Zn from infant foods containing increasing amounts of phytate, and to quantify the effect of the phytate:Zn molar ratio on the availability. During the in vitro assay, digestive conditions of infants, younger and older than 4 months of age, were carefully simulated since the solubility of phytate-Zn complexes during digestion is pH dependent. Availability was measured with a continuous flow dialysis in vitro procedure with previous intralumen digestive stage. Zn concentrations were determined with flame atomic absorption spectrometry. Phytic acid content was measured with HPLC. Adding phytate to infant formula lowered Zn availability to 2.84 (sd 0.17) % when the phytate:Zn molar ratio increased to 2.2 as compared with cows' milk-based formula (6.65 (sd 0.55) %). Availability from vegetables (23.83 (sd 2.17) %) significantly decreased at a ratio > 7.9 (15.12 (sd 1.63) %). Zn availability from soyabean-based formula (2.26 (sd 0.36) %) was lower compared with cows' milk-based formula (6.65 (sd 0.55) %). Availability between soyabean- and cows' milk-based formula was similar when a phytate:Zn ratio of 2.2 (2.84 (sd 0.17) %) was obtained in the cows' milk formula. The negative effect of phytic acid on Zn availability was dependent on the type of the food and the phytate content, and should be considered when using soyabean-based formulas during early infancy.

Effect of thickening agents, based on soluble dietary fiber, on the availability of calcium, iron, and zinc from infant formulas

Although it is accepted that dietary fiber probably is not needed in the diets of infants younger than 1 y, babies suffering from regurgitation are often fed with infant formulas thickened with considerable amounts of fiber. The effect of increasing amounts of alginic acid, locust-bean gum, and guar gum was studied from casein and whey-based infant formulas. A dialysis in vitro method with preliminary intraluminal digestion, adapted to the conditions of infants younger than 6 mo, was used. Human milk was used as the reference standard. Elemental contents of samples and dialysates were determined by atomic absorption spectrometry. Soluble dietary fiber inhibited mineral availability more in casein than in whey-based formulas. Mineral availabilities from casein- and whey-based formulas supplemented with 0.42 g of locust-bean gum/100 mL were 9.4% (0.7) and 10.4% (0.6) for calcium (P < 0.05), 0.32% (0.08) and 1.45% (0.17) for iron (P < 0.05), and 3.2% (0.2) and 5.6% (0.5) for zinc (P < 0.05), respectively. Calcium availability from the whey formula decreased in the presence of each fiber source, especially guar gum and alginic acid. Supplementing 2 g of alginic acid-based agents per 100 mL depressed calcium availability from 13.3% (1.2) to 5.3% (0.3; P < 0.05). With respect to iron and zinc, availabilities increased from 1.28% (0.28) to 6.05% (0.96; P < 0.05) and from 6.7% (0.6) to 10.2% (1.0), respectively, with the addition of 2 g of alginic acid (P < 0.05). Both gums lowered iron and zinc availabilities, and guar gum affected iron availability more severely than locust-bean gum did. Iron availabilities were 1.45% (0.17) from formula thickened with locust-bean gum (0.42 g/100 mL) and 0.92% (0.15) from formula thickened with guar gum (P < 0.05). Adding thickening agents based on soluble dietary fiber to traditional infant formulas probably affects calcium, iron, and zinc availability in various ways.

Binding of mineral elements to locust bean gum influences availability in vitro

Experiments were conducted to evaluate the extent to which element binding of locust bean gum (LBG) affects the availability of calcium, iron, and zinc in the gut. Infant formula was supplemented with increasing amounts of LBG and subjected to an intraluminal digestion procedure. Element binding was measured by eliminating the complexes by twofold centrifugation. Availability of the elements was determined using a validated continuous-flow dialysis technique. Elemental content of the samples, supematants, and dialysates was analyzed with validated atomic absorption spectrometry. LBG provided small amounts of intrinsic calcium (1.13+/-0.02 mg/g) and trace amounts of iron (0.02+/-0.00 mg/g) and zinc (0.01+/-0.00 mg/g), which were strongly bound to the LBG molecule (respectively: 76.6+/-3.3%, 83.4+/-1.2%, 96.7+/-6.6%). Correlation analysis, between percent element bound by LBG after centrifugation and percent trapped after dialysis, yielded significant correlation only for the data of zinc (r = 0.93). For calcium and iron, no correlation could be demonstrated; however, for iron a similar trend was observed. These findings suggest that element binding of LBG has a major influence on the availability of zinc and maybe of iron. For calcium, other factors might also be involved, affecting availability.

A method for in vitro determination of calcium, iron and zinc availability from first-age infant formula and human milk

A method for in vitro determination of available calcium, iron and zinc content from infant food after digestion was evaluated. This method introduced an intraluminal digestive phase, adapted to the gastrointestinal conditions of infants younger than 6 months of age, prior to continuous flow dialysis of the resultant gastric digest. Precautions handling the method were discussed and enzymatic parameters were defined. Ruggedness of the method was determined from the availability of calcium, iron and zinc at different gastrointestinal conditions. Availability of all three elements was higher at gastric pH of 2 (20.0 +/- 1.1% for calcium, 4.06 +/- 0.66% for iron and 17.5 +/- 1.3% for zinc), than from the normal procedure (pH 4) (15.6 +/- 1.2% for calcium, 1.18 +/- 0.26% for iron and 8.2 +/- 0.9% for zinc). At pH 5, however, calcium availability appeared to be lower (11.7 +/- 1.0%) (P < 0.05). The intestinal pH also had a major influence on the availability. At low intestinal pH (5.5), availability was 40.5 +/- 2.3% for calcium, 3.01 +/- 0.58% for iron and 26.8 +/- 1.8% for zinc, which was higher compared with the normal procedure (P < 0.05). Moreover, other factors, such as digestion time, mixing and filtration pressure, also affected the availability. Recovery tests yielded mean values of 94 +/- 3% for calcium, 109 +/- 9% for iron and 106 +/- 4% for zinc. Mean intra- and inter-batch precision of the availability procedure was 4.1 CV% and 6.6 CV% for calcium, 14.5 CV% and 19.2 CV% for iron, and 4.0 CV% and 13.6 CV% for zinc. The method provides adequate accuracy, acceptable precision and good recovery. It offers the advantage of being simple, rapid and inexpensive, since it takes only 1 day to run the whole availability procedure (including four replicates per sample), and the low costs of the dialysis equipment. It can therefore be considered as suitable for predicting the availability of essential elements from foods used during the first months of infancy.

In vitro availability of calcium, iron, and zinc from first-age infant formulae and human milk

BACKGROUND

Variation in the bioavailability of calcium (Ca), iron (Fe), and zinc (Zn) occurs because of interactions of food components in the gastrointestinal microenvironment. Bioavailability is preferably determined by in vivo tests, but these are expensive, labor-intensive, time consuming, and often unethical. As an alternative, in vitro methods can be used to predict bioavailability of nutrients from foodstuffs.

METHODS

A continuous-flow dialysis model with preliminary intraluminal digestive phase, adapted to the gastrointestinal conditions of infants younger than 6 months, was used. Human milk was the reference standard. Ca, Fe, and Zn content of samples and dialysates after digestion were analyzed by atomic absorption spectrometry.

RESULTS

Ca availability is similar in human milk (13.1%+/-0.8%), whey (13.3%+/-1.2%), and soy-based formulae (13.0%+/-1.2%; P > 0.05), and higher in casein-predominant formula (21.2%+/-0.6%; P < 0.05). Availability of Fe is highest in human milk (8.12%+/-0.27%: P < 0.05). Fe availability in whey (1.28%+/-0.28%) and soy formulae (1.48%+/-0.28%) is similar (P > 0.05), but availability is lower in casein-predominant formula (0.48%+/-0.22%; P < 0.05). Zn availability is also highest in human milk (13.1%+/-0.7%; P < 0.05). However, Zn availability is similar in whey (6.7%+/-0.6%) and casein formulae (8.5%+/-1.6%; P > 0.05), but lower in soy formula (2.3%+/-0.4%; P < 0.05).

CONCLUSIONS

Our observations are in agreement with previous data from in vivo studies in term infants. This in vitro procedure is an inexpensive, simple, rapid, and reliable method that predicts the bioavailability of Ca, Fe, and Zn in foods.

Thickening infant formula with digestible and indigestible carbohydrate: availability of calcium, iron, and zinc in vitro

BACKGROUND

Regurgitation is common in infants and is usually due to gastroesophageal reflux. Often parental reassurance and dietary management by feeding thickened formulas are the only therapeutic steps necessary. Adding fibers may interfere with the absorption of micronutrients.

METHODS

A continuous-flow dialysis in vitro method with a preliminary intraluminal digestive phase, modified to simulate the conditions of infants less than 6 months of age and children from 6 months of age on, was used to study the availability of calcium, iron, and zinc from thickened and nonthickened first-and second-age infant formulas. Pooled mature human milk was used as the reference standard. The elemental content of the samples and dialysate fractions of calcium, iron, and zinc after digestion was determined by atomic absorption spectrometry.

RESULTS

In human milk, calcium, iron, and zinc were highly available for absorptive processes. Availability of calcium, iron, and zinc from nonthickened first- and second-age infant formulas tends to be significantly better than in the corresponding products thickened with locust bean gum. Thickening infant formulas with pregelatinized rice starch, however, does not affect the availability of calcium, iron, and zinc.

CONCLUSIONS

It appears that human milk provides optimal conditions for the availability of calcium, iron, and zinc. Availability of calcium, iron, and zinc seems to lower when infant formulas are thickened with indigestible carbohydrates, whereas it does not by adding digestible carbohydrates.