Progress 07/01/20 to 12/31/23
Outputs
Target Audience:The target audience for this project is academic food and nutrition scientists, and scientists working in product development in the food industry. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?We initially envisioned one master's student would do most of the work for this project. However, after the project started there was the COVID shutdown, and we were not able to find a student. We sought and received permission from NIFA to use undergraduate students instead. So, all of the feeding and animal maintenance was completed by a cohort of three undergraduate students. How have the results been disseminated to communities of interest?We are currently preparing a manuscript to submit for publication in a peer-reviewed journal. In addition, we have submitted an abstract for a meeting on Probiotics, Prebiotics and Gut Microbiota in Prague in the summer of 2024. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Our main goal for this project was to feed mice a physiologically relevant mixture of dietary fiber at multiple levels, and to determine the effects on metabolic health and the composition and metabolic activity of the gut microbiome. While mice are the most commonly model organisms used in microbiome studies, the translational relevance to humans is unclear. In many studies, mice are fed fiber at levels impossible to achieve in human diets, which calls into question the relevance of the results. Conversely, most purified rodent diets only contain cellulose as the fiber source, which is also not relevant to human diets either. In this project, we worked to a) feed mice mixed fiber profiles at different levels, which were derived from recommended human diets and expected to have a physiological effect and to b) determine if they had effects on metabolism and also on the gut microbiome. Using a one-day meal plan recommended by the Institute of Medicine to provide adequate fiber, we used an in-silico approach to determine the relative proportion of cellulose, hemicellulose, lignin, pectin and beta-glucan consumed in one day. We then added this fiber blend into a high fat rodent diet at the 50%, 100% and 150% of recommended intakes. As comparators, we had a fiber-rich whole food diet (i.e. chow) and a low fat semi purified diet. The low-fat diets were used as negative controls, with one being a whole food-based diet, and the other a low-fat diet that had very little fiber. In humans, increasing dietary fiber intake is associate with lower adiposity and better glucose sensitivity, and subsequently lower levels of type 2 diabetes. Mice fed high fat diets develop obesity and also insulin resistance, and we hypothesized that increasing dietary fiber would prevent this. Contrary to our hypothesis, there were no difference in weight gain, or in body fat percentage, as measure by MRI in mice fed the high fat diets with different fiber levels. We conducted oral glucose and insulin tolerance tests at week 15, and there were no differences in mice fed the different fiber levels. For weight gain, body composition, food intake and oral glucose and insulin tolerance, we used a one-way ANOVA to compare the groups. These results indicate that simply adding more fiber to a poor-quality rodent diet does not mitigate the effects of weight gain and metabolic regulation. A second objective of this project was to evaluate how increasing the level of fiber in the diet affects the gut microbiome and production of short chain fatty acids. As mentioned previously, most purified mouse diets only contain cellulose as a fiber source, which is not thought to be fermented to a great extent. Perhaps for this reason, mice maintained on semi purified diets across generations have been shown to lose microbiome diversity and richness. Consequently, we hypothesized that providing mice a mixture of dietary fiber types would have effects on both the microbiome and the gene expression in the colon epithelia. To address this second objective, we conducted a phylogenetic profiling of the cecal microbiome, and also extracted and sequenced the messenger RNA from the colon epithelia. We hypothesized that mice fed the chow diet would have significantly different microbiomes than mice fed the purified diets. In addition, we hypothesized increasing fiber in the high fat diets would also affect the microbiome. In the microbiome analysis, we did find interesting differences between groups, as we had predicted. There were differences in alpha diversity, which is a measure of how many different species are in a group, as well as in beta diversity. This metric measures the relatedness between groups. As we expected, mice fed the chow diet had very different microbiomes than mice fed both the low-fat purified diet, and the high fat diets with added fiber. In some cases, there were features of the microbiome that distinctly separated chow fed mice from the other groups, like the bacterium Lactococcus lactis. This microbe is resent in high levels in the mice fed all the purified diets, but not chow. This is most likely because the purified diets use casein, a protein isolated from milk, as the sole protein source. Another major difference between the mice fed the different diets was the level of fecal short chain fatty acids. For the chow diet, mice had significantly more acetate, propionate and butyrate in their cecal contents, which are the main three short chain fatty acids found in feces. However, between the other diets there were no significant differences. Based on the information above, it appears that the background diet can significantly drive the community profile of the cecal microbiome. However, what about within a diet? Our high fat diets differed only in the content of fiber, as previously mentioned and spanned the range of 50% to 150% the recommended daily intake. One of the questions we are interested in is whether this can affect the microbiome. When the microbiomes from mice fed the low, medium and high fiber diets were compared, there were no major differences. Purified rodent diets are prepared from staple ingredients that are consistent across time and location. In this way, they resemble what are now called 'ultra processed' foods. The protein source in most semipurified diets is casein, lard makes up the bulk of the fat. To this, starch and sugars are added, as well as a vitamin and mineral mix. Chow, on the other hand, is a rodent food that is composed primarily of whole foods, like grains and fish meal. Chow contains over five times the amount of dairy fiber as semipurified diets, and the composition and metabolic activity of the gut microbiome reflect these differences. While dietary fiber is associated with better metabolic health in human epidemiological studies, it is not clear why. Fiber is often categorized into being either insoluble or soluble, which roughly translates to non fermentable and fermentable. Mechanistically, there is more reason to expect soluble fiber to be beneficial for health, as it slows digestion, binds bile acids, and provides fermentation substrates for the microbiome. Insoluble fiber, on the other hand, is not thought to be very fermentable. Yet, in prospective cohort studies, it is typically insoluble fiber that is associated with health benefits. Prior to formulating the diets for this study, we analyzed the fiber content of several recommended human high fiber diets. Consistently, we found that foods that are recommended as good fiber sources typically contain about 80% insoluble fiber and 20% soluble fiber. The diets in this study contained this ratio. What we can conclude from this work is that when fiber is added to a metabolically stressful diet, there appears to be little in the way of a metabolic health benefit.
Publications
- Type:
Conference Papers and Presentations
Status:
Under Review
Year Published:
2024
Citation:
An abstract for a poster presentation was submitted to the International Science Confernece, Probiotics, Prebiotics Gut Microbiota and Health that will take place in June of 2024.
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Progress 07/01/22 to 06/30/23
Outputs
Target Audience:The target audience for this project is academic food and nutrition scientists, and scientists working in product development in the food industry. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?This project was run entirely by undergraduate students in the Department of Nutrition, Dietetics and Food Sciences at Utah State University. In this reporting period, three students contributed to the project. How have the results been disseminated to communities of interest?Two posters were presented in this period, as previously described. What do you plan to do during the next reporting period to accomplish the goals?The last report period will be dedicated to data analysis.
Impacts
What was accomplished under these goals?
In this reporting period, we conducted an 18-week feeding study in mice. Mice were given either a chow or low fat purified diets (controls) or a high fat diet with low, medium or high dietary fiber. The fiber added to the high fat diets was a mixture of cellulose, hemicellulose, lignin, pectin and beta glucan. The relative proportions of these fibers was determined by doing an in silico analysis of a one day recommended high fiber diet published by the Institute of Medicine (IOM). The levels reflected the 50%, 100% and 150% amount of fiber recommended by the IOM. Food intake, weight gain, and body composition were measured during the study. In addition, we measured oral glucose and insulin tolerance at week 15. We also collected data on therespiratory exchange ratio. After the feeding period, mice were sacrificed and various tissues were measured and frozen. A one cm section of the colon was used to extract mRNA for gene expression analysis. In addition, we collected cecal contents for microbiome and short chain fatty acid analysis. In human prospective cohort studies, increasing intake of dietary fiber is associated with lower adiposity, and better metabolic health. We hypothesized that adding fiber to the high fat diet would protect mice against the weight gain, but that was not the case. Mice fed the high fat diets gained significantly more weight than mice fed the chow and low fat diets. In addition, addition fiber to the high fat diets did not improve metabolic health, as measured by the oral glucose tolerance test and insulin tolerance test.
Publications
- Type:
Other
Status:
Published
Year Published:
2023
Citation:
'Does fiber reduce weight gain and improve metabolism?' Bethany Sky Jones poster presenter, Utah State University Undergraduate Research Symposium, April 2023
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2023
Citation:
'Effect of Optimizing Fiber Intake of Mice on Weight Gain, Fat Mass, Oral Glucose and Insulin Tolerance Tests in Mice Fed a High Fat Diet' Kayden Stevenson presenter. Presented at American Society for Nutrition meeting Boston Massachutts. This poster was presented in 2022, but we failed to add it to that progress report.
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Progress 07/01/21 to 06/30/22
Outputs
Target Audience:The target audience for this project is academic food and nutrition scientists, and scientists working in product development in the food industry. In this reporting period, results from this study were disseminated at a departmental seminar, and at those who attended the American Society for Nutrition Meeting in the summer of 2022. Changes/Problems:None What opportunities for training and professional development has the project provided?This study was conducted by three undergraduates. They took care of the mice, collected body composition data by MRI, and assisted with the OGTT and ITTs. In addition, the undergraduates also collected the microbiome and short chain fatty acid data and conducted the fecal calprotectin analysis by ELISA. How have the results been disseminated to communities of interest?Two students presented at the ASN conference in June, and PI Ward presented preliminary results in a departmental seminar. What do you plan to do during the next reporting period to accomplish the goals?We will complete the data analysis and prepare a manuscript detailing the work.
Impacts
What was accomplished under these goals?
We completed a feeding study with mice fed diets that had levels and types of fiber that reflect human intakes. In the middle of the 16 week study and at the end, we conducted glucose and insulin tolerance tests and also determined body composition by MRI. At the termination of the study, we measured the fecal and cecal microbiome, fecal and cecal short chain fatty acids, and fecal calprotectin, a measure of gut inflammation. Increasing the fiber intake in micefrom the typical US intake (i.e. ~8g/1000 kcal) to the recommended intake (~i.e. ~14g/1000kcal) did not affect metabolic parameters, nor were there major changes in the microbiome composition or short chain fatty acids in the cecum and feces. However, there was a significant decrease in the cecal calprotectin levels in the mice fed the high fiber diet.
Publications
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Progress 07/01/20 to 06/30/21
Outputs
Target Audience:The target audience for this project is food and nutrition scientists, in academia, government and industry. Changes/Problems:We proposed to utilize an MS student for this project. However, we were not able to recruit one in time, and had several talented undergraduates to run the project. What opportunities for training and professional development has the project provided?The project was intented to utilize an MS student, but we were unable to recruit an MS student to start in a timely fashion. However, two undergradates in Dr. Ward's lab and one undergraduate in Dr. Hintze's lab were deemed to be sufficient to complete the project. Subsequently, a fourth undergraduate was available in the summer of 2021 due to an internship program. All four students have been training on methods of mouse handling, metabolic measurements, and also on microbiome measures. How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?We plan to start the 16 week feeding study in the middle of September. The feeding study should be completed in early January. We plan to conduct analyses on collected samples in January and February, and then write manuscripts and reports until the project ends in June.
Impacts
What was accomplished under these goals?
If mice are effective surrogates for humans, the mouse microbiome should respond to intakes of dietary fiber that are associated with better metabolic health in humans. To date, we have conducted an in silico analysis of a diet recommended for adequate dietary fiber by the Institute of Medicine. We have then sourced ingredients to formulate diets that will provide different amounts of fiber. Prior to diet formation, we also analyzed the fiber sources to ensure they would not affect micronutrient intakes. Large additions of dietary fiber to rodent pellets can possibly cause problems with pelleting. If the pellets are not sufficiently solid, they will fractionate when the mice eat them, and this will make determining the dietary intake very challenging. We are currently working with a scientist at Envigo Labs to determine if the high fiber diets can be effectively pelleted. Once this issue is addressed, we will order the diets and start the feeding study.
Publications
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