Dietary Fibre Consensus from the International Carbohydrate Quality Consortium (ICQC)

Dietary fibre is a generic term describing non-absorbed plant carbohydrates and small amounts of associated non-carbohydrate components. The main contributors of fibre to the diet are the cell walls of plant tissues, which are supramolecular polymer networks containing variable proportions of cellulose, hemicelluloses, pectic substances, and non-carbohydrate components, such as lignin. Other contributors of fibre are the intracellular storage oligosaccharides, such as fructans. A distinction needs to be made between intrinsic sources of dietary fibre and purified forms of fibre, given that the three-dimensional matrix of the plant cell wall confers benefits beyond fibre isolates. Movement through the digestive tract modifies the cell wall structure and may affect the interactions with the colonic microbes (e.g., small intestinally non-absorbed carbohydrates are broken down by bacteria to short-chain fatty acids, absorbed by colonocytes). These aspects, combined with the fibre associated components (e.g., micronutrients, polyphenols, phytosterols, and phytoestrogens), may contribute to the health outcomes seen with the consumption of dietary fibre. Therefore, where possible, processing should minimise the degradation of the plant cell wall structures to preserve some of its benefits. Food labelling should include dietary fibre values and distinguish between intrinsic and added fibre. Labelling may also help achieve the recommended intake of 14 g/1000 kcal/day.

Dietary Glycemic Index and Load and the Risk of Type 2 Diabetes: Assessment of Causal Relations

While dietary factors are important modifiable risk factors for type 2 diabetes (T2D), the causal role of carbohydrate quality in nutrition remains controversial. Dietary glycemic index (GI) and glycemic load (GL) have been examined in relation to the risk of T2D in multiple prospective cohort studies. Previous meta-analyses indicate significant relations but consideration of causality has been minimal. Here, the results of our recent meta-analyses of prospective cohort studies of 4 to 26-y follow-up are interpreted in the context of the nine Bradford-Hill criteria for causality, that is: (1) Strength of Association, (2) Consistency, (3) Specificity, (4) Temporality, (5) Biological Gradient, (6) Plausibility, (7) Experimental evidence, (8) Analogy, and (9) Coherence. These criteria necessitated referral to a body of literature wider than prospective cohort studies alone, especially in criteria 6 to 9. In this analysis, all nine of the Hill’s criteria were met for GI and GL indicating that we can be confident of a role for GI and GL as causal factors contributing to incident T2D. In addition, neither dietary fiber nor cereal fiber nor wholegrain were found to be reliable or effective surrogate measures of GI or GL. Finally, our cost–benefit analysis suggests food and nutrition advice favors lower GI or GL and would produce significant potential cost savings in national healthcare budgets. The high confidence in causal associations for incident T2D is sufficient to consider inclusion of GI and GL in food and nutrient-based recommendations.

Dried fruit and public health - what does the evidence tell us?

A scientific workshop held in the UK explored the potential contribution of traditional dried fruits to public health, identified gaps in the evidence and addressed priorities for research. Presentations considered the categorisation and composition of dried fruits; dried fruit and gastrointestinal health; the polyphenol content of dried fruits and their potential contribution to health; dried fruit and appetite in relation to the psychology of snacking and obesity; dried fruit and dental health including its role as a snack; and conflicts in public health advice for dried fruits. A round table discussion explored the contribution of dried fruit to "five a day" fruit and vegetable intake and fibre intake, whether dried fruits have equivalence with fresh in terms of dietary advice, advice on snacking in relation to dental health and appetite control, informing the public about different types of dried fruits and avoiding consumer confusion, and future research requirements.

Smokeless tobacco use: pattern of use, knowledge and perceptions among rural Bangladeshi adolescents

Background

The aim of the study was to investigate the practice and pattern of smokeless tobacco (SLT) use as well as the knowledge and perception about its ill effects among rural Bangladeshi adolescents.

Methods

A cross-sectional survey was conducted among students aged 13-18 years in two rural secondary schools in Bangladesh in August 2015. Data were collected through a self-administered questionnaire which consists of topics derived from the Social Cognitive Theory and Health Belief Model (personal characteristics, environmental factors, self-efficacy, outcome expectancies, perceived susceptibility, perceived severity, perceived benefits, perceived barriers, and cues to action). Data analysis was performed using SPSS version 24. A descriptive analysis was conducted to determine the current pattern of SLT use and knowledge about its ill effects. A chi-square test and Fisher exact test were conducted to explore associations between variables. Lastly, a logistic regression model was used to locate the predictors for current SLT use.

Results

A total of 790 students participated in the study. Among them, 9.5% (75) had used SLT at least once and 3.7% (29) were current SLT users. Males had a higher incidence of SLT use compared with females. The majority of students (77.3%) initiated SLT use between 10-13 years of age. 'Zarda' was the most common type of SLT used and most of the current users (86%) were able to buy SLT without age restrictions. Most of the current users (90%) wanted to quit SLT immediately; however, professional help was not available in schools. Overall, students had a good knowledge about the harmful effects of SLT with 54.8% (428) of respondents scoring in the good knowledge category. However, the majority of never SLT users (55.4%; 396) had a good knowledge compared to ever SLT users (42.7%; 32). Significant predictors of current SLT use included being a student aged 14 years and above (OR = 6.58, 95% CI [2.23-28.31]) as well as the variables of self-efficacy (OR = 5.78, 95% CI [1.46-19.65]), perceived barriers (OR = 0.30, 95% CI [0.10-0.74]), perceived benefit (OR = 0.21, 95% CI [0.05-1.03]) and perceived severity (OR = 0.36, 95% CI [0.16-0.91]).

Discussion

This study demonstrates the need for comprehensive prevention and control programme in rural schools targeting young adolescents. Effective measure should be taken to reshape the attitude of rural adolescents towards self-confidence and competence, as to prevent SLT use.

Short-term effects of a low glycemic index carob-containing snack on energy intake, satiety, and glycemic response in normal-weight, healthy adults: Results from two randomized trials

OBJECTIVES

The potential positive health effects of carob-containing snacks are largely unknown. Therefore, the aims of these studies were to determine the glycemic index (GI) of a carob snack compared with chocolate cookie containing equal amounts of available carbohydrates and to compare the effects of a carob versus chocolate cookie preload consumed as snack before a meal on (a) short-term satiety response measured by subsequent ad libitum meal intake, (b) subjective satiety as assessed by visual analog scales and (c) postprandial glycemic response.

METHODS

Ten healthy, normal-weight volunteers participated in GI investigation. Then, 50 healthy, normal-weight individuals consumed, crossover, in random order, the preloads as snack, with 1-wk washout period. Ad libitum meal (lunch and dessert) was offered. Capillary blood glucose samples were collected at baseline, 2 h after breakfast, just before preload consumption, 2 h after preload, 3 h after preload, just before meal (lunch and dessert), 1 h after meal, and 2 h after meal consumption.

RESULTS

The carob snack was a low GI food, whereas the chocolate cookie was a high GI food (40 versus 78, respectively, on glucose scale). Consumption of the carob preload decreased the glycemic response to a following meal and to the individual's feelings of hunger, desire to eat, preoccupation with food, and thirst between snack and meal, as assessed with the use of visual analog scales. Subsequently, participants consumed less amounts of food (g) and had lower total energy intake at mealtimes.

CONCLUSIONS

The carob snack led to increased satiety, lower energy intake at meal, and decreased postmeal glycemic response possibly due to its low GI value. Identifying foods that promote satiety and decrease glycemic response without increasing the overall energy intake may offer advantages to body weight and glycemic control.

Conformation and mobility of the arabinan and galactan side-chains of pectin

The function of the arabinan and galactan side-chains of pectin remains unknown. We describe 13C NMR experiments designed to yield spectra from the most mobile polymer components of hydrated cell walls isolated from a range of plant species. In pectin-rich cell walls, these corresponded to the pectic side-chains. The arabinan side-chains were in general more mobile than the galactans, but the long galactan side-chains of potato pectin showed high mobility. Due to motional line-narrowing effects these arabinan and galactan chains gave 13C NMR spectra of higher resolution than has previously been observed from 'solid' biopolymers. These spectra were similar to those reported for the arabinan and galactan polymers in the solution state, implying time-averaged conformations resembling those found in solution. The mobility of the highly esterified galacturonan in citrus cell walls overlapped with the lower end of the mobility range characteristic of the pectic side-chains. The cellulose-rich cell walls of flax phloem fibres gave spectra of low intensity corresponding to mobile type II arabinogalactans. Cell walls from oat coleoptiles appeared to contain no polymers as mobile as the pectic arabinans and galactans in primary cell walls of the other species examined. These properties of the pectic side-chains suggest a role in interacting with water.

Structure of cellulose-deficient secondary cell walls from the irx3 mutant of Arabidopsis thaliana

In the Arabidopsis mutant irx3, truncation of the AtCesA7 gene encoding a xylem-specific cellulose synthase results in reduced cellulose synthesis in the affected xylem cells and collapse of mature xylem vessels. Here we describe spectroscopic experiments to determine whether any cellulose, normal or abnormal, remained in the walls of these cells and whether there were consequent effects on other cell-wall polysaccharides. Xylem cell walls from irx3 and its wild-type were prepared by anatomically specific isolation and were examined by solid-state NMR spectroscopy and FTIR microscopy. The affected cell walls of irx3 contained low levels of crystalline cellulose, probably associated with primary cell walls. There was no evidence that crystalline cellulose was replaced by less ordered glucans. From the molecular mobility of xylans and lignin it was deduced that these non-cellulosic polymers were cross-linked together in both irx3 and the wild-type. The disorder previously observed in the spatial pattern of non-cellulosic polymer deposition in the secondary walls of irx3 xylem could not be explained by any alteration in the structure or cross-linking of these polymers and may be attributed directly to the absence of cellulose microfibrils which, in the wild-type, scaffold the organisation of the other polymers into a coherent secondary cell wall.

Conformational features of crystal-surface cellulose from higher plants

Native cellulose in higher plants forms crystalline fibrils a few nm across, with a substantial fraction of their glucan chains at the surface. The accepted crystal structures feature a flat-ribbon 21 helical chain conformation with every glucose residue locked to the next by hydrogen bonds from O-3' to O-5 and from O-2 to O-6'. Using solid-state NMR spectroscopy we show that the surface chains have a different C-6 conformation so that O-6 is not in the correct position for the hydrogen bond from O-2. We also present evidence consistent with a model in which alternate glucosyl residues are transiently or permanently twisted away from the flat-ribbon conformation of the chain, weakening the O-3' - 0-5 hydrogen bond. Previous molecular modelling and the modelling studies reported here indicate that this 'translational' chain conformation is energetically feasible and does not preclude binding of the surface chains to the interior chains, because the surface chains share the axial repeat distance of the 21 helix. Reduced intramolecular hydrogen bonding allows the surface chains to form more hydrogen bonds to external molecules in textiles, wood, paper and the living plant.

A definition for dietary fibre

The objective of this paper is to present a definition for dietary fibre based on recent advances that have taken place not only in human nutrition but also in plant cell-wall science and animal nutrition. We propose a physiologically based framework definition but, recognizing the diversity of dietary fibre, we have proposed further classifications within this framework. We also suggest that dietary fibre be removed from the carbohydrate group of nutrients because some compounds defined as dietary fibre are not chemically carbohydrates. The definition and classification system clearly highlight areas where further studies are needed.

Fine structure in cellulose microfibrils: NMR evidence from onion and quince

It has been controversial for many years whether in the cellulose of higher plants, the microfibrils are aggregates of 'elementary fibrils', which have been suggested to be about 3.5 nm in diameter. Solid-state NMR spectroscopy was used to examine two celluloses whose fibril diameters had been established by electron microscopy: onion (8-10 nm, but containing 40% of xyloglucan as well as cellulose) and quince (2 nm cellulose core). Both of these forms of cellulose contained crystalline units of similar size, as estimated from the ratio of surface to interior chains, and the time required for proton magnetisation to diffuse from the surface to the interior. It is suggested that the onion microfibrils must therefore be constructed from a number of cellulose subunits 2 nm in diameter, smaller than the 'elementary fibrils' envisaged previously. The size of these subunits would permit a hexagonal arrangement resembling the cellulose synthase complex.