Anne M. Raggio

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.

Effects of Resistant Starch, A Non-digestible Fermentable Fiber, on Reducing Body Fat

Objective: To assess the effects of energy dilution with non‐fermentable and fermentable fibers on abdominal fat and gut peptide YY (PYY) and glucagon‐like peptide (GLP)‐1 expressions, three rat studies were conducted to: determine the effects of energy dilution with a non‐fermentable fiber, compare similar fiber levels of fermentable and non‐fermentable fibers, and compare similar metabolizable energy dilutions with fermentable and non‐fermentable fibers.

Peptide YY and Proglucagon mRNA Expression Patterns and Regulation in the Gut

Objective: Peptide YY (PYY) and glucagon‐like peptide‐1 are important in the control of energy homeostasis and are both secreted from the gut in response to ingested nutrients. However, more studies are needed on nutrient regulation of their gene expression patterns in specific areas of the gut. This study detailed PYY and proglucagon (the gene that encodes glucagon‐like peptide‐1) gene expression patterns and regulation in the gut. We further examined the regulation of PYY and proglucagon mRNA by a diet containing fermentation‐resistant starch (in vivo) and butyrate (in vitro).

Dietary resistant starch increases hypothalamic POMC expression in rats.

Resistant starch (RS) is fermentable dietary fiber. Inclusion of RS in the diet causes decreased body fat accumulation and altered gut hormone profile. This study investigates the effect of feeding RS on the neuropeptide messenger RNA (mRNA) expressions in the arcuate nucleus (ARC) of the hypothalamus and whether vagal afferent nerves are involved. The rats were injected intraperitoneally with capsaicin to destroy unmyelinated small vagal afferent nerve fibers. The cholecystokinin (CCK) food suppression test was performed to validate the effectiveness of the capsaicin treatment. Then, capsaicin‐treated rats and vehicle‐treated rats were subdivided into a control diet or a RS diet group, and fed the corresponding diet for 65 days. At the end of study, body fat, food intake, plasma peptide YY (PYY) and glucagon‐like peptide 1 (GLP‐1), and hypothalamic pro‐opiomelanocortin (POMC), neuropeptide Y (NPY), agouti‐related peptide (AgRP) gene expressions were measured. RS‐fed rats had decreased body fat, increased POMC expression in the hypothalamic ARC, and elevated plasma PYY and GLP‐1 in both the capsaicin and vehicle‐treated rats. Hypothalamic NPY and AgRP gene expressions were not changed by RS or capsaicin. Therefore, destruction of the capsaicin‐sensitive afferent nerves did not alter the response to RS in rats. These findings suggest that dietary RS might reduce body fat through increasing the hypothalamic POMC expression and vagal afferent nerves are not involved in this process. This is the first study to show that dietary RS can alter hypothalamic POMC expression.

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.

Dietary-resistant starch improves maternal glycemic control in Goto-Kakizaki rat

SCOPE Dietary prebiotics show potential in anti-diabetes. Dietary resistant starch (RS) has a favorable impact on gut hormone profiles, including glucagon-like peptide-1 (GLP-1) consistently released, a potent anti-diabetic incretin. Also RS reduced body fat and improved glucose tolerance in rats and mice. In the current project, we hypothesize that dietary-resistant starch can improve insulin sensitivity and pancreatic β cell mass in a type 2 diabetic rat model. Altered gut fermentation and microbiota are the initial mechanisms, and enhancement in serum GLP-1 is the secondary mechanism. METHODS AND RESULTS In this study, GK rats were fed an RS diet with 30% RS and an energy control diet. After 10 wk, these rats were mated and went through pregnancy and lactation. At the end of the study, pancreatic β cell mass, insulin sensitivity, pancreatic insulin content, total GLP-1 levels, cecal short-chain fatty acid concentrations and butyrate producing bacteria in cecal contents were greatly improved by RS feeding. The offspring of RS-fed dams showed improved fasting glucose levels and normal growth curves. CONCLUSION Dietary RS is potentially of great therapeutic importance in the treatment of diabetes and improvement in outcomes of pregnancy complicated by diabetes.

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.

Dietary whey protein decreases food intake and body fat in rats

We investigated the effects of dietary whey protein on food intake, body fat, and body weight gain in rats. Adult (11–12 week) male Sprague‐Dawley rats were divided into three dietary treatment groups for a 10‐week study: control. Whey protein (HP‐W), or high‐protein content control (HP‐S). Albumin was used as the basic protein source for all three diets. HP‐W and HP‐S diets contained an additional 24% (wt/wt) whey or isoflavone‐free soy protein, respectively. Food intake, body weight, body fat, respiratory quotient (RQ), plasma cholecystokinin (CCK), glucagon like peptide‐1 (GLP‐1), peptide YY (PYY), and leptin were measured during and/or at the end of the study. The results showed that body fat and body weight gain were lower (P < 0.05) at the end of study in rats fed HP‐W or HP‐S vs. control diet. The cumulative food intake measured over the 10‐week study period was lower in the HP‐W vs. control and HP‐S groups (P < 0.01). Further, HP‐W fed rats exhibited lower N2 free RQ values than did control and HP‐S groups (P < 0.01). Plasma concentrations of total GLP‐1 were higher in HP‐W and HP‐S vs. control group (P < 0.05), whereas plasma CCK, PYY, and leptin did not differ among the three groups. In conclusion, although dietary HP‐W and HP‐S each decrease body fat accumulation and body weight gain, the mechanism(s) involved appear to be different. HP‐S fed rats exhibit increased fat oxidation, whereas HP‐W fed rats show decreased food intake and increased fat oxidation, which may contribute to the effects of whey protein on body fat.

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.