Browsing by Subject "Microbiota"

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    Satiety, glycemic, and gastrointestinal effects of novel fibers
    (2012-06) Klosterbuer, Abby Susan
    Epidemiological studies have shown that dietary fiber consumption is inversely associated with body weight, and some research suggests that foods high in fiber increase satiety and reduce energy intake. The mechanism for this relationship is unknown, but may be related to changes in glucose, insulin, or gut hormone concentrations. Fiber may also benefit health by improving laxation, altering the gut microbiota, and increasing production of short chain fatty acids (SCFA). The following work describes two review articles, as well as an intervention study designed to help examine these effects. The first review focuses on the benefits of dietary fiber in clinical nutrition. This allowed for evaluation of the physiological effects of different types and combinations of fiber in subjects on a controlled diet. In general, blends of fibers with varying physicochemical properties provided greater benefits and were better tolerated than single fiber sources. Next, a systematic review of the effects of fiber intake on gut hormone concentrations examined the evidence for this relationship. Considerable variation was found in study design, population, fiber type and dose, which made comparisons difficult. Few studies reported a significant effect of fiber on gut hormone levels, and data suggest caloric load may have a more significant influence. Lastly, a randomized, double-blind, crossover study examined the effects of three novel fibers with varying physicochemical properties on satiety, stool characteristics, and the role of gut hormones, glucose, and insulin in appetite regulation. On Day 1 of the study, healthy men and women consumed either a low-fiber control breakfast or 1 of 4 iii breakfasts containing 25 g fiber from soluble corn fiber (SCF) or resistant starch (RS), alone or in combination with pullulan (SCF+P and RS+P). Subjects rated satiety using visual analog scales (VAS), and blood samples were collected at various time points for 3 hours following breakfast. The fiber treatments did not influence satiety or energy intake compared to control. The RS+P treatment significantly reduced glucose, insulin, and GLP-1 concentrations. To examine the effects of chronic fiber intake, subjects consumed the fiber treatments at home for 6 additional days, with a 3 week washout between periods. Stool samples were collected on Day 7 and tolerance was assessed following fiber intake on Day 1 and Day 6. Fiber did not alter stool weight or stool consistency. SCF reduced pH and increased total SCFA production compared to control, while RS+P increased the percentage of butyrate. Overall, fiber was well tolerated, although treatments containing pullulan tended to cause minor increases in symptoms. Both SCF treatments resulted in a significant shift in the microbial community. Results from these studies confirm that different fibers vary in their physiological effects, and consuming fiber from a variety of sources may be most beneficial. Although increased satiety and improved bowel function are commonly reported benefits of fiber intake, it is clear that not all fibers exert these effects. In addition, the relationship between fiber and potential biomarkers of satiety remains unclear. Thus, it is important to evaluate the effects of different fibers in human studies to better guide recommendations for their use.
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    Wild Primate Gut Microbiota Protect Against Obesity
    (2017-04) Sidiropoulos, Dimitrios, N; Clayton, Jonathan; Al-Ghalith, Gabe; Shields-Cutler, Robin; Ward, Tonya; Blekhman, Ran; Kashyap, Purna; Knights, Dan
    The gastrointestinal tract hosts trillions of bacteria that play major roles in metabolism, immune system development, and pathogen resistance. Although there is increasing evidence that low dietary fiber in Westernized societies is associated with dramatic loss of natural human gut microbiome diversity, the role of this loss in obesity and inflammation is not well understood. Non-human primates (NHPs) can be used as model systems for studying the effects of diet and lifestyle disruption on the human gut microbiome. Captive primates are typically exposed to low-fiber diets and tend to have human-associated microbiota in place of their native microbiota. In order to explore interactions between the gut microbiota and dietary fiber, we transplanted captive and wild primate gut microbiota into germ-free mice and then exposed them to either a high- or low-fiber diet. We found that the group receiving low-fiber diet and captive primate microbiota became obese and had high levels of circulating inflammatory cytokines, while mice receiving high-fiber diet and wild primate microbiota remained healthy. Mice with the wild primate microbiota and low-fiber diet acquired intermediate levels of obesity, demonstrating an interaction between dietary fiber and the microbiota. These results show that the modern human gut microbiome interacts with low-fiber diets to cause inflammation and obesity, and suggest a possible clinical role for manipulation of the microbiota in the treatment of obesity.