Exploring the Gut, the Brain, and Beyond: Q&A with Dr. Marc Tetel, Ph.D.
Exploring the Gut, the Brain, and Beyond: Q&A with Human Microbiome and Neuroscience Researcher Dr. Marc Tetel, Ph.D.
I recently had a fascinating discussion with friend and PTP client, Marc Tetel, Ph.D. Marc is the Allene Lummis Russell Professor in Neuroscience at Wellesley College where his research lab is currently examining the link between lifestyle choices and the female microbiome. A couple months back I got to pick his brain and wanted to share his expertise. The following is a Q&A between Marc and me:
Could you provide a quick overview of your background in neuroscience how it led to you researching the human microbiome?
Like most researchers, I’ve had a winding path to where I am today. I received my BA in Biology from Northwestern University. After traveling and then working in a research lab, I decided to pursue a PhD in Neuroscience, which I did at the University of Massachusetts at Amherst. At UMass, I studied how the ovarian hormones, estradiol and progesterone, acted in the brain to influence behavior. In my postdoctoral fellowship at the University of Colorado Health Sciences Center, I left neuroscience to study the molecular mechanisms of progesterone receptors in breast cancer. In establishing my own lab, I returned to neuroscience to explore the molecular mechanisms of hormones in brain and the regulation of behavior. My lab at Wellesley then became interested in how estrogens regulate metabolism in females. An example of estrogens impacting metabolism is during menopause when estrogen levels decrease causing weight gain in women, which is associated with increased risk of obesity, type 2 diabetes and cancer. We then began asking if the gut microbiome may be contributing to some of these effects of estrogens on metabolism. More recently, we’ve been exploring how the gut microbiome is involved in stress and if it interacts with other microbiomes (more below).
Popular awareness about the gut microbiome and its links to health status and disease have been increasing significantly over the couple decades. Could you provide a brief update on the current understanding of the importance of the microbiome and implications in health/disease?
The gut microbiota consists of all the microorganisms that live in the gut, including bacteria, viruses, and fungi. These microorganisms, their genes, and the chemicals they produce make up the gut microbiome. The gut microbiome (GM) aids in the digestion of food, protects against pathogens, and maintains the immune system. However, it’s also been implicated in a variety of diseases and disorders, including obesity, irritable bowel syndrome, diabetes, and different types of cancer. In addition, the gut microbiome can influence how the brain functions and the brain can impact the gut microbiome. This two-way relationship is referred to as the gut microbiome-brain axis. Disturbance of this gut microbiome-brain axis has been implicated in a variety of brain disorders, including anxiety, depression, Alzheimer’s Disease, Parkinson’s Disease, and autism. So, we’re finding out that the gut microbiome has profound effects on human physiology and disease. However, with up to 500 species of bacteria in the gut microbiome, it’s complicated and challenging to figure out how the GM is impacting these disorders.
How plastic is the microbiome in a healthy adult? What lifestyle factors/ diets/etc. promote a healthy or diverse microbiome?
The GM is very plastic during the first couple years of life, and then stabilizes more as we age. However, the GM is influenced by a number of lifestyle factors throughout life, the most prominent being one’s diet. A healthy GM is diverse, so in regard to bacteria, this means it consists of a number of different species. A diet of a variety of foods, including fresh fruits, vegetables, whole grains, and high-fiber foods (just like your mother always said), promotes a diverse and healthy GM. In addition, fermented foods, such as kimchi, kombucha, yogurt and sauerkraut, which contain probiotics, also promote a diverse microbiome. Other lifestyle factors, such as exercise and sleep, are important for maintaining a healthy GM. Conversely, eating processed foods, a high fat diet, or excess sugar, can decrease the diversity and promote a less healthy GM. In addition, high levels of stress or excess alcohol have been associated with a less diverse and less healthy GM. So, there are many things we can all do to help support a healthy GM, including maintaining a healthy diet and sleep habits, exercising (and staying active by going to PT Progression!), minimizing our alcohol, and managing our stress.
I recall during our last conversation that you made the statement to the effect of 'let your kids eat dirt and swim in scum ponds'. As a recovering germophobe, and a parent to young kids, I found a lot of solace in this shift from thinking of dirt as a potential pathogen towards something that may actually be a helpful exposure. I think what you were talking about is in line with what's popularly known as the Hygiene Hypothesis, is that correct?
The hygiene hypothesis says that children need to be exposed to “germs” to develop a healthy immune system, suggesting that an extremely clean household environment can produce a less developed immune system. In support of this idea, there are studies showing that children raised in households with furry pets have a more diverse GM. One study even shows that children raised with dogs have increased levels of bacteria that may protect against asthma and an immune system disorder (atopy). While the hygiene hypothesis needs to be studied further, I always encouraged my kids to get dirty and let the dog lick their face!
Probiotics have become a staple addition to many people's supplement regimens. Prebiotics have also been popping up in supplements and food products more and more. Could you explain the difference between pre- and probiotics? Is there any solid research supporting the use of either in healthy adults?
Probiotics are foods or supplements that contain live bacteria and other microorganisms that are thought to promote a healthy GM. Examples of sources of probiotics are fermented foods such as yogurt, sauerkraut, kombucha, and kimchi. Prebiotics provide food for gut bacteria and other microorganisms to increase their abundance. Sources of prebiotics are foods high in fiber, such as whole grains, soy beans, flax seed, apples and sweet potatoes. While there are some studies in animals and humans showing benefits of probiotics and prebiotics, more research needs to be done to determine the health benefits for humans. One thing to keep in mind is that each person’s gut microbiome is unique. So what may benefit one person, may not be a benefit to another person. While both probiotics and prebiotics are available as supplements at nutrition and health stores, it’s probably best for healthy adults to get their probiotics and prebiotics from natural food sources.
What are your predictions about what current/future research will reveal pertaining to the microbiome over the next ten years?
I think the future of human microbiome research is very exciting!
a) We’re getting a decent handle on the composition of the human GM. However, the next critical step is to understand the function of the GM. What are the bacteria and other microorganisms in the gut doing? And how are they doing it?
b) Also, while much of the focus has been on the bacteria (i.e. microbiota) of the gut microbiome, there is increasing interest in the function of viruses (mycobiome) in the GM.
c) While antibiotics have been extremely helpful in treating many disorders, they eliminate broad spectrums of microbes, which can cause some complicated and challenging side effects. It will be important for researchers to develop ways to target individual microbes (or groups of microbes) to eliminate (or increase) them in treating specific disorders.
d) We’ve all heard that the era of personalized/individualized medicine is approaching. This will be especially important, and challenging, in regard to the GM. As already discussed, each person’s GM is unique and will respond differently to treatments. So future research will need to study how diet and therapeutic approaches affects an individual’s specific microbiome.
e) Finally, I think exploring how different microbiomes affect each other is fascinating and important. For example, little is known about how the gut and vaginal microbiomes interact to impact women’s health. My lab is collaborating with colleagues at the Mayo Clinic to address this question and determine how lifestyle choices (such as diet, sleep, activity, stress) may affect this interaction.
I want to thank you, Marc, for taking the time to talk with us, share your knowledge, and also for your dedication to science. These insights are fascinating and I will surely think about you the next time a dog licks my kid’s face!
Disclaimer: The above is for informative and educational purposes only and does not constitute medical advice.