Gut Bacteria. June 2. Issue. Gut Bacteria. By Megan D. Baumler, Ph. D, RD, CDToday’s Dietitian. Vol. 4. 6Research suggests they may be therapeutic targets for obesity and chronic diseases. ![]() Suggested CDR Learning Codes: 2. Level 2. Take this course and earn 2 CEUs on our Continuing Education Learning Library. Imagine that foods are not calorically equal for every individual: A bran muffin may provide 2. Also imagine that these caloric differences all boil down to the type of bacteria living in someone’s colon, and that an individual may favorably influence these bacteria for optimal personal health. Recent research shows this may indeed be the case. There are 1. 0 times more bacterial cells in our bodies than there are actual human cells, and we house more bacterial genes than human genes. Not all bacteria are bad. In fact, most are good, including those that take up residence in our gastrointestinal (GI) tract. Our gut bacteria, also known as the gut flora or microbiome, rely on our bodies as a place to live. For their own survival, they promote our health in what is known as symbiosis, a mutually beneficial relationship. They rely on us and we rely on them. Diets profoundly affect gut bacteria. One recent study indicates a diet rich in animal products may be doing the most damage to our internal ecosystem. UCLA researchers now have the first evidence that bacteria ingested in food can affect brain function in humans. In an early proof-of-concept study of healthy women. When researchers tested the. When gut bacteria feed on certain foods — including eggs and beef — they produce a compound that could boost the risk of heart disease, according to a recent study. Chronic fatigue syndrome is a relatively mysterious condition. Breaking research that examines gut bacteria yields new clues and offers fresh hope. Because gut bacteria are anaerobic, making them exceptionally difficult to study, little has been known about their complex symbiotic relationship with our health. However, new research techniques—high throughput sequencing technology and the use of germ- free animal models—have allowed researchers to study gut flora in both animals and humans to gain a better understanding of their influence on our health. Researchers are examining the connection between specific gut flora profiles and health outcomes by looking for associations with certain health characteristics and those specific gut flora profiles. Most remarkable, given the obesity epidemic, is the finding that gut bacteria may contribute to a metabolic predisposition to obesity. It’s unclear whether the presence of specific gut flora is a contributor or consequence of obesity, but compelling evidence suggests a strong association. Researchers are looking for the determinants of individuals’ gut flora profiles to establish whether there are any potential therapeutic implications. Gut flora profiles differ among individuals, and diet is considered a primary determinant of a gut flora profile. This begs the question, could certain diets or foods be recommended on the basis of promoting a specific gut flora profile to positively influence health outcomes? This continuing education course explores the relationship among diet, gut flora, and health outcomes, and discusses the concept that gut flora may be a therapeutic target for obesity and related chronic diseases. Good Bugs. The development of a thriving gut flora begins at birth. In utero, the fetus lives in a sterile environment, but upon birth, babies are quickly inoculated with bacteria from their mothers, and by about age 1, they have a well- developed gut flora. Approximately 1. 00 trillion bacterial cells live in the GI tract, mostly in the large intestine. While colonic bacteria predominantly are from two bacterial phyla, Bacteroidetes and Firmicutes, there are about 4. Family members, however, share more similar gut flora than unrelated individuals. Gut bacteria have many critical functions, including supporting the normal development of the GI tract and immune system. Research has shown that germ- free animals (raised and maintained in sterile environments) have underdeveloped GI tracts and are susceptible to infection. In promoting the host’s immunity, the gut bacteria ensure that they won’t be taken over by pathogenic (disease- causing) bacteria. Friendly gut bacteria act as a physical barrier and also secrete antimicrobial proteins that prevent the colonization of pathogenic bacteria. In addition to supporting development of the GI tract and the immune system, gut bacteria synthesize essential nutrients, including biotin and vitamins B1. K, although not in sufficient enough quantities to meet our requirements. Gut bacteria also are capable of harvesting energy from food that’s indigestible in the upper small intestine. In doing so, they produce short- chain fatty acids, an energy substrate absorbed by colonic epithelial cells that’s either subsequently used for energy by the colonic cells themselves or absorbed into the bloodstream. While this energy the gut bacteria produces is beneficial to maintain colonic epithelial cells, in this age of obesity, the extra energy absorbed into the bloodstream isn’t exactly welcome. Researchers are examining the nature of this relationship by exploring the types of bacteria that affect our metabolism and the manner in which they do so, with provocative results so far. Backhed and colleagues conducted a landmark study in 2. In this study, germ- free mice were colonized with bacteria from the intestines of normal mice. The formerly germ- free mice also had greater carbohydrate absorption and increased triglyceride storage in their adipocytes. The authors concluded that the gut microbiota are an environmental factor—akin to diet and exercise—that regulate fat storage. Before modern times in which food is readily available, increased fat storage caused by gut bacteria would have been beneficial. But now, it intensifies the risk of obesity and the associated chronic diseases that are rampant in the population. Even more intriguing is a follow- up study in which germ- free mice were colonized with gut bacteria from obese or lean mice. The germ- free mice that were colonized with bacteria from obese mice had a 4. Characterization of the gut flora profile of the obese and lean mice revealed that the former had more Firmicutes compared with the Bacteroidetes type, suggesting that it was the difference in gut flora profile that led to the increased fat accumulation since it was the only variable in the study that changed between the groups. Furthermore, the gut flora in the obese mice’s colons was found to have greater capacity to ferment indigestible carbohydrate. In a related study by Turnbaugh and colleagues, when mice were “humanized” with fecal flora from humans and switched from a low- fat, high- plant- polysaccharide diet to a Western- style high- fat, high- sugar diet, dramatic changes occurred in the gut flora within one day and resulted in increased fat stores. This study showed that specific diet patterns result in changes in gut flora and subsequent health outcomes, lending support to the notion that we may favorably influence our gut flora profile through diet. To see whether gut bacteria profiles predicted weight status, researchers analyzed the fecal microbiota of infants and compared gut flora profiles with weight status later in life. Children who became overweight or obese had less Bifidobacteria in their gut flora during infancy and through childhood compared with children who maintained a normal weight. This is the only prospective study to date that followed subjects over time to explore a connection between gut flora and weight status, and it found that specific gut flora profiles precede development of overweight, suggesting potential causation. This study didn’t control for other variables that may have contributed to weight status, such as diet, so conclusions are limited. Regardless of whether the relationship is causal, it’s clear that obesity is associated with a certain gut flora. Ley and colleagues found that a mouse model of obesity by leptin resistance had a 5. Bacteroidetes and an increase in Firmicutes bacteria in their gut flora. The association between obesity and gut flora is less clear in human studies because of inconsistent findings, possibly related to differences in research techniques. Another interesting study by Ley and colleagues found key differences in the gut flora between people who were obese and lean. People who were obese had more Firmicutes compared with Bacteroidetes bacteria in their gut flora, and more importantly, following one year of significant weight loss through dietary changes, formerly obese individuals had gut flora that was more similar to that of lean individuals. To date, studies indicate that obesity is associated with changes in the gut flora. While some evidence suggests that gut bacteria may be causally linked to obesity, it’s still too early to determine the exact nature of the relationship. Differences in research methodologies and the complexity of human subjects, their diets, and gut flora prevent definitive conclusions. More recently, studies have focused on defining enterotypes (certain gut flora profiles) and characterizing gut flora by the metabolic profiles, such as the capacity to harvest energy, rather than by traditional lineage of phylum, genus, and species. There are multiple ways to characterize gut flora profiles; the most valuable method is the one that holds true most consistently and may lead to the development of novel therapeutic approaches for obesity and other metabolic disorders. A subject of controversy is whether it’s more useful to categorize gut bacteria by lineage or metabolic potential for purposes of developing a therapeutic approach to obesity. It’s unclear whether the effect of diet on gut flora and the association between gut flora and health outcomes become more apparent with one or the other classification scheme. Until a consensus on this is reached, it’s difficult to conduct reviews and meta- analyses for more convincing results because of differences in methods of classifying gut profiles. Diseases Related to Obesity. The relationship between gut bacteria and chronic disease risk may go beyond obesity. This isn’t surprising, since obesity increases the risk of other diseases and because metabolic changes, as purported to occur with changes in gut flora, may alter risk of diseases other than obesity. Insulin Resistance. The groundbreaking study from Backhed and colleagues in 2.
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