Effect of mastication on lipid bioaccessibility of almonds in a randomized human study and its implications for digestion kinetics, metabolizable energy, and postprandial lipemia

Background: The particle size and structure of masticated almonds impact significantly on nutrient release (bioaccessibility) and digestion kinetics. Objectives: To quantify the effects of mastication on the bioaccessibility of intracellular lipid of almond tissue and examine microstructural characteristics of masticated almonds. Design: In a randomized, subject-blind, crossover trial, 17 healthy subjects chewed natural (NA) or roasted almonds (RA) on 4 separate mastication sessions. Particle size distributions (PSDs) of the expectorated boluses were measured using mechanical sieving and laser diffraction (primary outcome). The microstructure of masticated almonds, including the structural integrity of the cell walls (i.e. dietary fiber), was examined using microscopy. Lipid bioaccessibility was predicted using a theoretical model, based on almond particle size and cell dimensions, and then compared to empirically-derived release data. Results: Inter-subject variations (n=15, 2 subjects withdrew) in PSDs of both NA and RA samples were small (e.g. laser diffraction, CV = 12% and 9%, respectively). Significant differences in PSDs were found between these two almond forms (P 500 µm) in masticated almonds. Microstructural examination of the almonds indicated that most intracellular lipid remained undisturbed in intact cells post-mastication. No adverse events were recorded. Conclusions: Following mastication, most of the almond cells remained intact with lipid encapsulated by cell walls. Thus, most of the lipid (>88%) in masticated almonds is not immediately bioaccessible and remains unavailable for digestion and absorption. The lipid encapsulation mechanism provides a convincing explanation for why almonds have a low metabolizable energy content and an attenuated impact on postprandial lipemia. Trial registration number; ISRCTN58438021

Manipulation of starch bioaccessibility in wheat endosperm to regulate starch digestion, postprandial glycemia, insulinemia, and gut hormone responses: a randomized controlled trial in healthy ileostomy participants

Background: Cereal crops, particularly wheat, are a major dietary source of starch, and the bioaccessibility of starch has implications for postprandial glycemia. The structure and properties of plant foods have been identified as critical factors in influencing nutrient bioaccessibility; however, the physical and biochemical disassembly of cereal food during digestion has not been widely studied. Objectives: The aims of this study were to compare the effects of 2 porridge meals prepared from wheat endosperm with different degrees of starch bioaccessibility on postprandial metabolism (e.g., glycemia) and to gain insight into the structural and biochemical breakdown of the test meals during gastroileal transit. Design: A randomized crossover trial in 9 healthy ileostomy participants was designed to compare the effects of 55 g starch, provided as coarse (2-mm particles) or smooth (0.2-mm particles) wheat porridge, on postprandial changes in blood glucose, insulin, C-peptide, lipids, and gut hormones and on the resistant starch (RS) content of ileal effluent. Undigested food in the ileal output was examined microscopically to identify cell walls and encapsulated starch. Results: Blood glucose, insulin, C-peptide, and glucose-dependent insulinotropic polypeptide concentrations were significantly lower (i.e., 33%, 43%, 40%, and 50% lower 120-min incremental AUC, respectively) after consumption of the coarse porridge than after the smooth porridge (P , 0.01). In vitro, starch digestion was slower in the coarse porridge than in the smooth porridge (33% less starch digested at 90 min, P , 0.05, paired t test). In vivo, the structural integrity of coarse particles (~2 mm) of wheat endosperm was retained during gastroileal transit. Microscopic examination revealed a progressive loss of starch from the periphery toward the particle core. The structure of the test meal had no effect on the amount or pattern of RS output. Conclusion: The structural integrity of wheat endosperm is largely retained during gastroileal digestion and has a primary role in influencing the rate of starch amylolysis and, consequently, postprandial metabolism. This trial was registered at isrctn.org as ISRCTN40517475