June Zhou

Dietary resistant starch upregulates total GLP-1 and PYY in a sustained day-long manner through fermentation in rodents.

Glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) are anti-diabetes/obesity hormones secreted from the gut after meal ingestion. We have shown that dietary-resistant starch (RS) increased GLP-1 and PYY secretion, but the mechanism remains unknown. RS is a fermentable fiber that lowers the glycemic index of the diet and liberates short-chain fatty acids (SCFAs) through fermentation in the gut. This study investigates the two possible mechanisms by which RS stimulates GLP-1 and PYY secretion: the effect of a meal or glycemic index, and the effect of fermentation. Because GLP-1 and PYY secretions are stimulated by nutrient availability in the gut, the timing of blood sample collections could influence the outcome when two diets with different glycemic indexes are compared. Thus we examined GLP-1 and PYY plasma levels at various time points over a 24-h period in RS-fed rats. In addition, we tested proglucagon (a precursor to GLP-1) and PYY gene expression patterns in specific areas of the gut of RS-fed rats and in an enteroendocrine cell line following exposure to SCFAs in vitro. Our findings are as follows. 1) RS stimulates GLP-1 and PYY secretion in a substantial day-long manner, independent of meal effect or changes in dietary glycemia. 2) Fermentation and the liberation of SCFAs in the lower gut are associated with increased proglucagon and PYY gene expression. 3) Glucose tolerance, an indicator of increased active forms of GLP-1 and PYY, was improved in RS-fed diabetic mice. We conclude that fermentation of RS is most likely the primary mechanism for increased endogenous secretions of total GLP-1 and PYY in rodents. Thus any factor that affects fermentation should be considered when dietary fermentable fiber is used to stimulate GLP-1 and PYY secretion.

The intestinal microbiota in aged mice is modulated by dietary resistant starch and correlated with improvements in host responses.

Dietary interventions might prevent or reverse age-related declines in health through modification of the activity and composition of the intestinal microbiota. As a first step toward more comprehensive evaluations of single dietary components on healthy aging, 16S rRNA gene amplicon sequencing was applied to determine the structure of the bacterial communities in the ceca of 20-month-old healthy mice fed energy-controlled diets containing 0, 18, or 36% type 2 resistant starch (RS) from high-amylose maize (HAM-RS2). The cecal microbiota of mice fed a diet depleted in RS and containing the readily digestible carbohydrate amylopectin were dominated by bacteria in the Firmicutes phylum and contained low levels of Bacteroidetes and Actinobacteria. In contrast, mice fed diets containing HAM-RS2 were colonized by higher levels of Bacteroidetes and Bifidobacterium, Akkermansia, and Allobaculum species in proportions that were dependent on the concentration of the dietary fiber. The proportions of Bifidobacterium and Akkermansia were positively correlated with mouse feeding responses, gut weight, and expression levels of proglucagon, the precursor of the gut anti-obesity/diabetic hormone GLP-1. This study showed that aging mice harbor a distinct microbiota, which can be modulated by RS and enriched for bacteria that are associated with improved health.

Role of Resistant Starch in Improving Gut Health, Adiposity, and Insulin Resistance

The realization that low-glycemic index diets were formulated using resistant starch led to more than a decade of research on the health effects of resistant starch. Determination of the metabolizable energy of the resistant starch product allowed for the performance of isocaloric studies. Fermentation of resistant starch in rodent studies results in what appears to be a healthier gut, demonstrated by increased amounts of short-chain fatty acids, an apparent positive change in the microbiota, and increased gene expression for gene products involved in normal healthy proliferation and apoptosis of potential cancer cells. Additionally, consumption of resistant starch was associated with reduced abdominal fat and improved insulin sensitivity. Increased serum glucagon-like peptide 1 (GLP-1) likely plays a role in promoting these health benefits. One rodent study that did not use isocaloric diets demonstrated that the use of resistant starch at 8% of the weight of the diet reduced body fat. This appears to be approximately equivalent to the human fiber requirement. In human subjects, insulin sensitivity is increased with the feeding of resistant starch. However, only 1 of several studies reports an increase in serum GLP-1 associated with resistant starch added to the diet. This means that other mechanisms, such as increased intestinal gluconeogenesis or increased adiponectin, may be involved in the promotion of improved insulin sensitivity. Future research may confirm that there will be improved health if human individuals consume the requirement for dietary fiber and a large amount of the fiber is fermentable.

Failure to ferment dietary resistant starch in specific mouse models of obesity results in no body fat loss

UNLABELLED Resistant starch (RS) is a fermentable fiber that decreases dietary energy density and results in fermentation in the lower gut. The current studies examined the effect of RS on body fat loss in mice. In a 12 week study (study 1), the effect of two different types of RS on body fat was compared with two control diets (0% RS) in C57Bl/6J mice: regular control diet or the control diet that had energy density equal to that of the RS diet (EC). All testing diets had 7% (w/w) dietary fat. In a 16 week study (study 2), the effect of RS on body fat was compared with EC in C57BL/6J mice and two obese mouse models (NONcNZO10/LtJ or Non/ShiLtJ). All mice were fed control (0% RS) or 30% RS diet for 6 weeks with 7% dietary fat. On the seventh week, the dietary fat was increased to 11% for half of the mice and remained the same for the rest. Body weight, body fat, energy intake, energy expenditure, and oral glucose tolerance were measured during the study. At the end of the studies, the pH of cecal contents was measured as an indicator of RS fermentation. Compared with EC, dietary RS decreased body fat and improved glucose tolerance in C57BL/6J mice but not in obese mice. For other metabolic characteristics measured, the alterations by RS diet were similar for all three types of mice. The difference in dietary fat did not interfere with these results. The pH of cecal contents in RS fed mice was decreased for C57BL/6J mice but not for obese mice, implying the impaired RS fermentation in obese mice. CONCLUSIONS (1) decreased body fat by RS is not simply due to dietary energy dilution in C57Bl/6J mice, and (2) along with their inability to ferment RS, RS fed obese mice did not lose body fat. Thus, colonic fermentation of RS might play an important role in the effect of RS on fat loss.

High-amylose resistant starch increases hormones and improves structure and function of the gastrointestinal tract: a microarray study.

Background/Aims: Type 2 resistant starch from high-amylose maize (HAM-RS2) is associated with increased fermentation, increased expression of proglucagon (gene for GLP-1) and peptide YY (PYY) genes in the large intestine, and improved health. To determine what other genes are up- or downregulated with feeding of HAM-RS2, a microarray was performed. Methods: Adult, male Sprague Dawley rats were fed one of the following three diets for a 4-week study period: cornstarch control (CC, 3.74 kcal/g), dietary energy density control (EC, 3.27 kcal/g), and 30% HAM-RS2 (RS, 3.27 kcal/g). Rat microarray with ∼27,000 genes and validation of 94 representative genes with multiple qPCR were used to determine gene expression in total RNA extracts of cecal cells from rats. The RS versus EC comparison tested effects of fermentation as energy density of the diet was controlled. Results: For the RS versus EC comparison, 86% of the genes were validated from the microarray and the expression indicates promotion of cell growth, proliferation, differentiation, and apoptosis. Gut hormones GLP-1 and PYY were increased. Conclusions: Gene expression results predict improved structure and function of the GI tract. Production of gut hormones may promote healthy functions beyond the GI tract.

Resistant starch from high amylose maize (HAM‐RS2) and Dietary butyrate reduce abdominal fat by a different apparent mechanism

Obesity is a health concern. Resistant starch (RS) type 2 from high‐amylose maize (HAM‐RS2) and dietary sodium butyrate (SB) reduce abdominal fat in rodents. RS treatment is associated with increased gut hormones peptide YY (PYY) and glucagon‐like peptide 1 (GLP‐1), but it is not known if SB increases these hormones.

High fat diet partially attenuates fermentation responses in rats fed resistant starch from high-amylose maize

The effects of type 2 resistant starch from high‐amylose maize (HAM‐RS2) in rodents fed with low‐fat diets were demonstrated in previous studies. Fish oil is also reported to reduce body fat. In the current study, the effects of high fat and fish oil on HAM‐RS2 feeding in rats were investigated.

Resistant starch from high amylose maize (HAM-RS2) reduces body fat and increases gut bacteria in ovariectomized (OVX) rats†‡

Obesity after menopause is a health concern for older females. Changes in the microbiota are likely to occur with this condition. Modifying the microbiota with a prebiotic is a plausible strategy for improving the health of menopausal females.

The importance of GLP-1 and PYY in resistant starch's effect on body fat in mice.

Resistant starch (RS) is a dietary fermentable fiber that decreases body fat accumulation, and stimulates the secretion of glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) in rodents. GLP-1 and PYY are gut-secreted hormones with antiobesity effect. Thus, blocking the signals of increased GLP-1 and PYY may also block the effect of dietary RS on body fat. In a 10-week study, C57BL/6J and GLP-1 receptor null (GLP-1R KO) mice were fed control or 30% RS diet, and received daily intraperitoneal injection of either saline or PYY receptor antagonist (BIIE0246, 20 μg/kg body weight). Dietary RS significantly decreased body fat accumulation only in wild-type mice that has saline injection, but not in GLP-1R KO mice. PYY receptor antagonist diminished RS action on body fat in wild-type mice, but did not interfere with GLP-1R KO mice response to RS. Regardless of genotype and injection received, all RS-fed mice had increased cumulative food intake, cecal fermentation, and mRNA expression of proglucagon and PYY. Thus, our results suggest that increased GLP-1 and PYY is important in RS effects on body fat accumulation.

Tolerance, fermentation, and cytokine expression in healthy aged male C57BL/6J mice fed resistant starch

Health benefits of resistant starch (RS), a dietary fermentable fiber, have been well documented in young, but not in old populations. As the essential step of more comprehensive evaluations of RS on healthy aging, we examined the effects of dietary RS on tolerance, colonic fermentation, and cytokine expression in aged mice. Healthy older (18-20 months) C57BL/6J male mice were fed control, 18% RS, or 36% RS diets for 10 weeks. Body weight gain, body composition, and fat pad weights did not differ among the three groups after 10 weeks, indicating good tolerance of the RS diet. Fermentation indicators (cecum weights, and cecal proglucagon and PYY mRNA expression) were enhanced in an RS dose-dependent manner (p<0.01). Serum concentrations of soluble cytokine receptors (sTNF-Rb, sIL-4R, sIL-2Rα, sVEGFR1, and sRAGE) and TNFα expression (gene and protein) in visceral fat did not differ significantly among groups. Adiponectin protein concentrations, but not gene expression, were greater in epididymal fat of the 36% RS versus control groups (p<0.05). As a conclusion in aged mice, dietary RS is well tolerated, fermented in the colon, and stimulates colonic expression of proglucagon and PYY mRNA, and adiponectin protein in visceral fat.