A type 4 resistant potato starch alters the cecal microbiome and gene expression in mice fed a western diet based on NHANES data.

Four major types of resistant starch (RS1-4) are present in foods, all of which can alter the microbiome and are fermented in the cecum and colon to produce short-chain fatty acids (SCFAs). Type 4 RSs are chemically modified starches, not normally found in foods, but have become a popular food additive as their addition increases fiber content. Multiple studies, in humans and rodents, have explored how different RS4 affect post-prandial glucose metabolism, but fewer studies have examined the effects of RS4 consumption on the microbiome. In addition, many RS studies conducted in rodents use high-fat diets that do not approximate what is typically consumed by humans. To address this, mice were fed a Total Western Diet (TWD), based on National Health and Nutrition Examination Survey (NHANES) data that mimics the macro and micronutrient composition of a typical American diet, for six weeks, and then supplemented with 0, 2, 5, or 10% of the RS4, Versafibe 1490™ (VF), a phosphorylated and cross-linked potato starch, for an additional three weeks. The cecal contents were analyzed for SCFA content and microbiota composition. Butyrate production was increased while branched chain SCFA production decreased. The alpha-diversity of the microbiome decreased in mice fed the TWD with 10% VF 1490 added while the beta-diversity plot showed that the 5% and 10% VF groups were distinct from mice fed the TWD. Similarly, the largest changes in relative abundance of various genera were greatest in mice fed the 10% VF diet. To examine the effect of VF consumption on tissue gene expression, cecal and distal colon tissue mRNA abundance were analyzed by RNASeq. Gene expression changes were more prevalent in the cecum than the colon and in mice fed the 10% VF diet, but the number of changes was substantially lower than we previously observed in mice fed the TWD supplemented with native potato starch (RPS). These results provide additional evidence that the structure of the RS is a major factor determining its effects on the microbiome and gene expression in the cecum and colon.

Matched whole grain wheat and refined wheat milled products do not differ in glycemic response or gastric emptying in a randomized, crossover trial.

BACKGROUND: Epidemiologic and some clinical studies support the view that whole grain foods have lower glycemic response than refined grain foods. However, from the perspective of food material properties, it is not clear why whole grain cereals containing mostly insoluble and nonviscous dietary fibers (e.g., wheat) would reduce postprandial glycemia. OBJECTIVES: We hypothesized that glycemic response for whole grain wheat milled products would not differ from that of refined wheat when potentially confounding variables (wheat source, food form, particle size, viscosity) were matched. Our objective was to study the effect of whole grain wheat compared with refined wheat milled products on postprandial glycemia, gastric emptying, and subjective appetite. METHODS: Using a randomized crossover design, healthy participants (n = 16) consumed 6 different medium-viscosity porridges made from whole grain wheat or refined wheat milled products, all from the same grain source and mill: whole wheat flour, refined wheat flour, cracked wheat, semolina, reconstituted wheat flour with fine bran, and reconstituted wheat flour with coarse bran. Postprandial glycemia, gastric emptying, and appetitive response were measured using continuous glucose monitors, the 13C-octanoic acid (8:0) breath test, and visual analog scale (VAS) ratings. Bayes factors were implemented to draw inferences about null effects. RESULTS: Little-to-no differences were observed in glycemic responses, with lower incremental AUC between 0 and 120 min glycemic responses only for semolina [mean difference (MD): -966 mg min/dL; 95% CI: -1775, -156 mg min/dL; P = 0.02) and cracked wheat (MD: -721 mg min/dL; 95% CI: -1426, -16 mg min/dL; P = 0.04) than for whole wheat flour porridge. Bayes factors suggested weak to strong evidence for a null effect (i.e., no effect of treatment type) in glycemic response, gastric emptying, and VAS ratings. CONCLUSIONS: Although whole grain wheat foods provide other health benefits, they did not in their natural composition confer lower postprandial glycemia or gastric emptying than their refined wheat counterparts.This trial was registered at clinicaltrials.gov as NCT03467659.

Brown rice compared to white rice slows gastric emptying in humans.

BACKGROUND/OBJECTIVES: Consumption of whole vs. refined grain foods is recommended by nutrition or dietary guideline authorities of many countries, yet specific aspects of whole grains leading to health benefits are not well understood. Gastric emptying rate is an important consideration, as it is tied to nutrient delivery rate and influences glycemic response. Our objective was to explore two aspects of cooked rice related to gastric emptying, (1) whole grain brown vs. white rice and (2) potential effect of elevated levels of slowly digestible starch (SDS) and resistant starch (RS) from high-amylose rice. SUBJECTS/METHODS: Ten healthy adult participants were recruited for a crossover design study involving acute feeding and testing of 6 rice samples (50 g available carbohydrate). Gastric emptying rate was measured using a 13C-labeled octanoic acid breath test. A rice variety (Cocodrie) with high-amylose content was temperature-cycled to increase SDS and RS fractions. RESULTS: In vitro starch digestibility results showed incremental increase in RS in Cocodrie after two temperature cycles. For low-amylose varieties, SDS was higher in the brown rice form. In human subjects, low-amylose and high-amylose brown rice delayed gastric emptying compared to white rices regardless of amylose content or temperature-cycling (p < 0.05). CONCLUSIONS: Whole grain brown rice had slower gastric emptying rate, which appears to be related to the physical presence of the bran layer. Extended gastric emptying of brown rice explains in part comparably low glycemic response observed for brown rice.

Preload of slowly digestible carbohydrate microspheres decreases gastric emptying rate of subsequent meal in humans.

Gastric emptying rate influences how fast the nutrients of a meal are delivered to the body, and when slow, it moderates glycemic response and may impact satiety. Carbohydrates are one of the macronutrients that trigger the ileal brake, and we hypothesized that slowly digestible carbohydrate (SDC) administered in a premeal load would delay gastric emptying. A crossover design study was conducted with 10 healthy adults using fabricated SDC-microspheres (cooked) that were given 20 minutes before a non-nutritive viscous paste meal. There were 4 treatment arms, each separated by a 1-week washout period, consisting of (1) the paste alone, (2) a rapidly digesting maltodextrin (Polycose) preload followed by the paste 20 minutes later, (3) an SDC-microsphere preload followed by the paste, and (4) a comparably slower SDC-microsphere preload followed by the paste. A 13C-labeled octanoic acid breath test method was used to measure gastric emptying, with the label incorporated into the non-nutritive paste. The microspheres were less than 1 mm in diameter (a size that does not require breakdown in the stomach before emptying) and, after cooking, were of the same density value. Compared with the paste alone, both of the SDC-microsphere preloads (slow and comparably slower digesting) decreased gastric emptying rate of the paste, with the latter having the most effect (half-emptying times of 1.7, 2.3, and 2.8 hours, respectively [each different at P<.05]). In conclusion, SDCs decreased gastric emptying rate, and this was suggested to be due to a triggering of the ileal brake.