But health-conscious shoppers are not the only ones fixated on what is known as the gut microbiome—the populations of good microorganisms that inhabit our intestines.
Scientists, too, have their sights set on the intestines, as they try to unravel the connection between the microbiome and overall health.
“When we stop to consider that we have 100 trillion microorganisms inhabiting our intestines—that is 10 times the number of cells we have in our bodies—that begs the question of how the balance and function of these microbes affect our health, as well as how such balance can be disrupted by diet and even medicine,” said Beth McCormick, PhD, vice chair and professor of microbiology & physiological systems. Dr. McCormick studies intestinal inflammation resulting from foodborne pathogens and chronic inflammatory bowel diseases.
“While for years science has focused on the understanding of pathogenic microorganisms, it is key we also start to understand the beneficial microorganisms that work to keep us healthy,” she said.
To begin understanding the connection between gut bacteria and our health, we first need to know about the bacteria that live on and within us. Bacteria colonize almost every surface of our bodies including our skin, nasal passages, mouth and intestines, and the populations of bacteria differ between locations. Joshua Lederberg, PhD, who won the Nobel Prize for Physiology or Medicine in 1958 for his work on bacterial genetics, coined the term “microbiome” in 2001 to “signify the ecological community of commensal, symbiotic and pathogenic microorganisms that literally share our body space and have been all but ignored as determinants of health and disease.”
A variety of studies have indicated the human gut is home to about one hundred trillion bacteria representing various species referred to as a whole as the gut microbiome. These bacteria help keep our intestines running smoothly by aiding in digestion and by protecting us from infections by outcompeting pathogens we ingest through contaminated food and water. We become colonized with bacteria from our mothers during birth, but as soon as we become exposed to bacteria from the food we eat and from elsewhere in our environments, we start to develop our own gut microbiomes. As long as these bacteria stay in the gut, they promote our health rather than making us sick. For example, we normally associate E. coli with foodborne illnesses, but there is actually a strain of E. coli that lives safely in our colons.
Current research into the gut microbiome includes understanding what species of bacteria live in our guts and, in particular, whether the presence or absence of a particular species puts us at risk for developing or acquiring different diseases. Already, studies done in germ-free mice (mice with no microbiomes) showed these mice are more susceptible to infections and have altered intestinal structure compared to normal mice. These, and other differences, were highlighted in a review written by Fergus Shanahan, MD, a gastrointestinal researcher at University College Cork, in which he discussed what was known about the gut microbiome as of 2002.
As the normal microbiome seems to have such an important role in maintaining health, many researchers think that disruptions in the microbiome populations, or their absence altogether, may put people at risk for developing certain conditions. For example, whether the gut microbiome has a role in chronic inflammatory bowel diseases such as ulcerative colitis and Crohn’s disease has been of interest for many years. According to the Crohn’s and Colitis Foundation of America, both conditions are marked by relapsing and often chronic states of intestinal inflammation, with Crohn’s disease capable of affecting any part of the digestive tract and ulcerative colitis affecting only the colon.
While the exact cause of both of these inflammatory bowel diseases is not fully understood and likely involves a series of genetic and environmental triggers, perturbations in the gut microbiome may play a role. Indeed, multiple studies have demonstrated that patients with either disease have differences in the composition of their gut microbiome compared to healthy individuals. These differences could cause the immune system to overreact in the gut.
Researchers are also investigating whether there is a connection between the gut microbiome and conditions such as autism, colon cancer and diabetes, to name a few. However, in determining the role of the gut microbiome in such diseases, researchers are often left with a chicken or the egg situation in which whether these conditions are caused by alterations in the gut microbiome or the conditions themselves cause an alteration in the gut microbiome is not always immediately clear.
In cases where a medical condition may result from abnormalities with the gut microbiome or with how the body responds to the gut microbiome, prebiotic and probiotics have the potential to serve as therapies. For example, the Alimentary Pharmabiotic Centre through the University College Cork advocates the research and development of treatment plans utilizing pharmabiotics, which they define as therapies that use “any material (including microbes or molecules) originating from the gut ecosystem that can be exploited for a health benefit.” This could include the use of prebiotics and probiotics to manage inflammatory bowel diseases and other conditions that have been linked to the gut microbiome.
Beyond the potential use of pharmabiotics to treat specific medical conditions, the prebiotics and probiotics industries have seen a boom in consumer popularity in recent years. These items are designed to promote health by maintaining the balance of good bacteria that live on and in us. Although their end goal is the same, they work in different ways. Prebiotics support the environments in which these bacteria live by adding specific nutrients, while probiotics actively add certain species of beneficial bacteria to our bodies.
Prebiotics and probiotics are one of the latest “get healthy, stay healthy” trends to hit our society. In fact, the American market for prebiotics is expected to double from where it was in 2011 to $220 million by 2015, while the European and American markets for prebiotics are together projected to reach nearly $1.4 billion by 2015. The global market for probiotics is expected to reach $32.6 billion by next year.
In comparison, the global market for vitamins is projected to reach $3.3 billion by 2015. Prebiotics and probiotics are marketed to help a variety of problems all while promoting general well-being. Despite the variety of conditions proposed to be helped by pro- and prebiotics, the industry is arguably most synonymous with promoting good digestion. Indeed, years before we could purchase specialized probiotic pills or creams, consumers were encouraged to consume yogurt with “live active cultures” to help maintain gut health.
While many of us may swear by the benefits of eating yogurt every day, and while much has been learned about the presence and importance of the gut microbiome in recent years, it’s important to remember that our understanding of the gut microbiome’s role in our health is still in its infancy. Like any young field of research, a lot of adjustments will likely be made with regard to how studies are performed and how data are analyzed as researchers uncover more information, and as technologies improve. McCormick suggested specifically that, “the field of microbiome research could benefit from the development of more robust tools for sample processing, analytical methods and new informatics approaches,” and that, “on the ‘human’ side, an increased number of participants, improvement in quality controls and long-term longitudinal studies are desperately needed.”
Indeed, the need for such advances offers a unique opportunity for collaboration across various scientific disciplines, as pointed out in a brief essay written by Jeffrey Gordon, MD, a leader in the field of gut microbiome research at Washington University in St. Louis, in the journal Science last year. He highlighted opportunities for partnerships amongst engineers, systems biologists and gut researchers to pave the way to innovative methods and technologies that will help improve how data are collected and analyzed.
That we have evolved from classifying bacteria as strictly harmful to acknowledging that they can benefit our health shows the magnitude of advances that are possible. The findings from this growing field are likely to be fascinating and perhaps surprising, so stay tuned.
“In the age of human health and nutrition awareness, bolstered in part by the obesity epidemic, that these microorganisms may tinker with our own physiology and metabolism, and thus might be at the forefront of disease or health, is of interest and captures the attention of us all—scientist or not,” McCormick said.