Published meta-analyses indicate significant but inconsistent incident type-2 diabetes (T2D)-dietary glycemic index (GI) and glycemic load (GL) risk ratios or risk relations (RR). It is now over a decade ago that a published meta-analysis used a predefined standard to identify valid studies. Considering valid studies only, and using random effects dose–response meta-analysis (DRM) while withdrawing spurious results (p < 0.05), we ascertained whether these relations would support nutrition guidance, specifically for an RR > 1.20 with a lower 95% confidence limit >1.10 across typical intakes (approximately 10th to 90th percentiles of population intakes). The combined T2D–GI RR was 1.27 (1.15–1.40) (p < 0.001, n = 10 studies) per 10 units GI, while that for the T2D–GL RR was 1.26 (1.15–1.37) (p < 0.001, n = 15) per 80 g/d GL in a 2000 kcal (8400 kJ) diet. The corresponding global DRM using restricted cubic splines were 1.87 (1.56–2.25) (p < 0.001, n = 10) and 1.89 (1.66–2.16) (p < 0.001, n = 15) from 47.6 to 76.1 units GI and 73 to 257 g/d GL in a 2000 kcal diet, respectively. In conclusion, among adults initially in good health, diets higher in GI or GL were robustly associated with incident T2D. Together with mechanistic and other data, this supports that consideration should be given to these dietary risk factors in nutrition advice. Concerning the public health relevance at the global level, our evidence indicates that GI and GL are substantial food markers predicting the development of T2D worldwide, for persons of European ancestry and of East Asian ancestry.

SummaryNative cellulose in higher plants forms crystalline ®brils a few nm across, with a substantial fraction of their glucan chains at the surface. The accepted crystal structures feature a¯at-ribbon 2 1 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¯at-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 2 1 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.

Solid-state nuclear magnetic resonance relaxation experiments can provide information on the rigidity of individual molecules within a complex structure such as a cell wall, and thus show how each polymer can potentially contribute to the rigidity of the whole structure. We measured the proton magnetic relaxation parameters T2 (spin-spin) and T,p (spin-lattice) through the 13C-nuclear magnetic resonance spectra of dry and hydrated cell walls from onion (Allium cepa L.) bulbs. Dry cell walls behaved as rigid solids. The form of their T, decay curves varied on a continuum between Caussian, as in crystalline solids, and exponential, as in more mobile materials. The degree of molecular mobility that could be inferred from the T2 and Tlp decay patterns was consistent with a crystalline state for cellulose and a glassy state for dry pectins. The theory of composite materials may be applied t o explain the rigidity of dry onion cell walls in terms of their components. Hydration made little difference to the rigidity of cellulose and most of the xyloglucan shared this rigidity, but the pectic fraction became much more mobile. Therefore, the cellulose/ xyloglucan microfibrils behaved as solid rods, and the most significant physical distinction within the hydrated cell wall was between the microfibrils and the predominantly pectic matrix. A minor xyloglucan fraction was much more mobile than the microfibrils and probably corresponded to cross-links between them. Away from the microfibrils, pectins expanded upon hydration into a nonhomogeneous, but much softer, almost-liquid gel. These data are consistent with a model for the stress-bearing hydrated cell wall in which pectins provide limited stiffness across the thickness of the wall, whereas the cross-linked microfibril network provides much greater rigidity in other directions.Little is known about the details of how the structure of plant cell walls gives them their rigidity and strength, and thus their ability to support the plant against the stresses of weather, gravity, and transpiration (Raven, 1977; Preston, 1979). Solid-state NMR spectrometry has the potential to provide a window into the internal stress-bearing properties of the cell wall. Magnetic relaxation data derived from NMR experiments allow the relative mobilities of individual polymers, and of functional groups within them, to be inferred (Abragam, 1961).Much of the relevant NMR methodology, and the theory for linking polymer mobility to bulk mechanical properties, have been developed for synthetic macromolecules (Schaefer et al., 1977;Kenwright and Say, 1993;McBrierty and Packer, 1994). Similar experiments have been carried out on plant cell walls (Irwin et al., 1984(Irwin et al., , 1985Newman et al., 1994Newman et al., , 1996 Foster et al., 1996;Ha et al., 1996), but the full transfer of the technology from synthetic polymers to hydrated biological materials such as the cell wall is not likely to be simple. It will require solutions to substantial experimental problems arising from the presence of wa...

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.

A resolution-enhanced 13C nuclear magnetic resonance (NMR) spectrum of cell wall material isolated from Braeburn apples has revealed a pair of signals assigned to cellulose chains exposed on crystal surfaces, providing evidence for a high degree of molecular ordering on those surfaces. Proton spin relaxation editing revealed no detectable amorphous cellulose and provided an estimate of about 23 chains in a typical crystallite. Cellulose in apple cell walls was found to be distinctive, with triclinic and monoclinic Id crystalline forms present in similar proportions. Hence, its composition is intermediate between the family of bacterial and Valonia celluloses, rich in the triclinic crystalline form, and the family of cotton and ramie celluloses, in which the monoclinic form is dominant. Implications for apple crispness are discussed.