Maren Hegsted

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).

Stabilized rice bran and oat bran lower cholesterol in humans

Abstract Dietary fibers such as cereal brans may be used as a tool to reduce blood cholesterol in hypercholesterolemic individuals. This study compared the effects of rice bran and oat bran in eleven human subjects with moderately-high blood cholesterol levels. In a 10-week controlled feeding trial, subjects consumed 100 g/day stabilized rice bran or 100 g/day oat bran for two 3-week periods in a crossover design. Prior to each bran phase, a control diet without bran was provided for 2 weeks. Total cholesterol levels decreased 7.0% when subjects consumed rice bran or oat bran. The decrease was primarily the result of a reduction in LDL-cholesterol. HDL- and VLDL- cholesterol, in addition to triglycerides were not significantly changed by either bran source. Rice bran was equally effective as oat bran in lowering blood cholesterl levels.

Creatine supplementation alters the response to a graded cycle ergometer test.

Abstract To determine the effects of creatine supplementation on cardiorespiratory responses during a graded exercise test (GXT) 36 trained adults (20 male, 16 female; 21–27 years old) performed two maximal GXTs on a cycle ergometer. The first GXT was done in a non-supplemented condition, and the second GXT was done following 7 days of ingesting either 5 g creatine monohydrate, encased in gelatin capsules, four times daily (CS, 13 male, 6 female), or the same number of glucose capsules (PL, 7 male, 10 female). CS significantly (P < 0.05) improved total test time [pre-CS=1217 (240) s, mean (std. dev.) versus post-CS=1289 (215) s], while PL administration had no effect (P > 0.05) on total test time [pre-PL=1037 (181) s versus post-PL=1047 (172) s]. In addition, both oxygen consumption (V˙O2) and heart rate at the end of each of the first five GXT stages were significantly lower after CS, but were unchanged after PL. Moreover, the ventilatory threshold occurred at a significantly greater V˙O2 for CS [pre-CS=2.2 (0.4) l · min−1 or 66% of peak V˙O2 versus post-CS=2.6 (0.5) l · min−1 or 78% of peak V˙O2; pre-PL=2.6 (0.9) l · min−1 or 70% peak V˙O2 versus post-PL=2.6 (1.1) l · min−1 or 68% of peak V˙O2]. Neither CS nor PL had an effect on peak V˙O2 [pre-CS=3.4 (0.7) l · min−1 versus post-CS=3.3 (0.7) l · min−1; pre-PL=3.7 (1.1) l · min−1 versus post-PL=3.7 (1.1) l · min−1]. Apparently, CS can alter the contributions of the different metabolic systems during the initial stages of a GXT. Thus, the body is able to perform the sub-maximal workloads at a lower oxygen cost with a concomitant reduction in the work performed by the cardiovascular system.

Effects of dietary chromium supplementation on cardiac mass, metabolic enzymes, and contractile proteins

Abstract Chromium, a popular but controversial micronutrient, can increase skeletal muscle growth when provided in supplemented quantities, presumably because of its suspected insulin like action. Whether chromium similarly affects cardiac muscle is an important issue because inappropriate cardiac growth can suggest decrements in cardiac performance. Therefore, the purpose of this study was to determine if chromium supplementation impacted contractile and metabolic properties of the heart. Male Sprague-Dawley rats received a semi-purified basal diet supplemented with 300 PPB chromium picolinate (CONTR), or supplemented with 1500 PPB chromium picolinate (SUPPLEM). After 12 weeks on the respective diets, animals were killed, and the left ventricles removed and analyzed for differences in cardiac metabolic and contractile proteins. Chromium supplementation failed to alter body weights, left ventricular mass, total protein content, and myofibrillar protein content, citrate synthase, or hexokinase activity. The amount of the high ATPase myosin isoform, V1 was diminished by 11% in the SUPPLEM group (p ≤ 0.05). These findings demonstrate that the adaptive response of the heart to dietary chromium supplementation is limited to changes in the myosin isoform. These changes may provide the heart with a more economical contractile apparatus without compromising cardiac performance.

DOSAGE EFFECTS OF CHROMIUM PICOLINATE ON GROWTH AND BODY COMPOSITION IN THE RAT

Abstract This 12-week study examined the effects of six different levels of dietary chromium (Cr) (0, 75, 150, 300, 600, 1500 ppb Cr) in the form of Cr picolinate (CrPic) upon growth and body composition in the rat. Ninety male Harlan Sprague-Dawley weanling rats arrived in three groups of 30 animals (referred to as Blocks 1, 2, and 3). Five animals from each block were assigned to each treatment resulting in a 6 × 3 (treatment X block) Randomized Block Design. Body composition was assessed via dual energy X-ray absorptiometry (DEXA). At Week 5, significant treatment X block interactions were found for fat weight and percent body fat (P ≤ 0.05), but there were only trends at Week 10 (P ≤ 0.10). These interactions reflected decreases in body fat for Block 1 that corresponded with increasing CrPic levels in the diet. No interactions nor treatment effects were seen for growth rate, lean body mass, or tissue weights, but most block effects were highly significant (P ≤ 0.01). A significant treatment X block interaction for feed intake (P = 0.01) revealed a decrease for Blocks 1 and 2, but an increase for Block 3, at the highest CrPic level. Except for the highest dietary level, body fat reductions for Block 1 occurred without decreases in feed intake, implicating a possible dietary-induced thermogenic effect of CrPic. It was concluded that genetic differences between the blocks of animals could have accounted for some of the differential effects of CrPic supplementation.

Suboptimal levels of dietary copper vary immunoresponsiveness in rats

The effects of severe, moderate, and mild copper deficiencies on cellular and humoral immunity were studied. Fifty male Sprague-Dawley rats, 5 wk of age, were fed diets containing 0.5, 2.0, 3.5, or 5.0 μg Cu/g for either 4 or 8 wk. Ten of the rats were fed the control diet, but were pair-fed with the 0.5-μg/g treatment group. All rats were immunized once with sheep red blood cells. Mean plasma-copper concentration reflected the dietary levels of copper, and ceruloplasmin activity correlated highly to plasma copper. Rats consuming suboptimal levels of copper responded differently to the deficiencies, so copper status varied among those animals. After 8 wk, cell proliferation, when stimulated by phytohemagglutinin, was dependent on the copper status of the animal. Severely deficient rats had consistently lower lymphocyte stimulation indexes for phytohemagglutinin and concanavalin A, but specific antibody response was not reduced. Immunoglobulin G (IgG) concentrations were variable for all rats, and immunoglobulin M (IgM) concentrations were lower for the severely deficient rats. Suboptimal dietary copper may alter immune function in rats, depending on the ensuing effect on copper status.

Recovery of Rats from Vitamin D-Deficient Mothers

Two separate studies were conducted using weanling rats from either an unsupplemented, low vitamin D colony or a supplemented, adequate vitamin D colony. Severe hypocalcemia, slower increases in body weight gain, and lower apparent calcium, magnesium, and phosphorus balance values occurred in the rats from the low vitamin D colony fed a purified AIN-76A, vitamin D-devoid diet compared to rats from the vitamin D-adequate colony fed the same diet. Apparent calcium, magnesium, and phosphorus balance values, as well as most other measurements, in rats from the low vitamin D colony fed a purified AIN-76a, vitamin D-adequate diet were greater than or equal to those of rats never subjected to low vitamin D. This was suggestive of overcompensation in recovery from low maternal vitamin D. However, rats from the low vitamin D colony fed an unrefined (chow), vitamin D-adequate diet had lower apparent balance and bone values compared with rats from the vitamin D-supplemented colony fed the same diet. Presumably high levels of calcium, magnesium, and phosphorous in the unrefined diet prevented any overcompensation during recovery, as occurred with purified diets, from the earlier vitamin D deficiency. Overall, results indicated weanling rats from a low vitamin D colony had low vitamin D stores and were marginally vitamin D-deficient. In addition, recovery from the marginal deficiency had occurred to a large extent after feeding a purified, vitamin D-adequate diet. The results suggest the use of low vitamin D colony rats as a model for human, marginal vitamin D deficiency.

The humoral immune response in marginally and severely magnesium deficient rats

Abstract The effects of severe, moderate, and mild magnesium deficiencies on plasma proteins, immunoglobulin M (IgM), immunoglobulin G (IgG), and specific antibody response were studied. Forty male Sprague-Dawley rats were fed diets containing 50, 160, 280, and 400 μg magnesium/gram for either three or eight weeks. Eight of the rats were fed the control diet but were pair fed with the 50 μg/gram treatment group. All rats were immunized once with sheep red blood cells. Plasma magnesium levels reflected the dietary levels of magnesium, and bone magnesium highly correlated with plasma magnesium. The severely deficient rats had significantly enlarged spleens, while all other groups were similar to controls. The severe magnesium deficiency significantly decreased total plasma proteins. Additionally, immunoglobulin M and G levels were significantly reduced in the severely deficient rats. The mean log antibody titer for the severely deficient rats was approximately half that of the controls, but was not statistically different from the other dietary groups. Conversely, total plasma proteins were not lowered by the suboptimal levels of magnesium. Immunoglobulin M levels in the marginally deficient animals correlated with their plasma magnesium concentrations, and lower immunoglobulin G levels were found with the moderate magnesium deficiencies. Antibody response was not altered by the suboptimal levels of dietary magnesium.