Gut-Microbiota-Brain Axis: Your questions answered from the webinar!

Licensed by R. Allen/Shutterstock

Over 280 participants attended the MFLN Nutrition and Wellness free webinar Gut-Microbiota-Brain Axis, presented by Dr. Hannah Holscher. This topic is so timely and in the news,

the questions kept flowing to the extent we ran out of time to answer them. As promised, Dr. Holscher has answered them in this blog post.

Dietitians can still earn 1 CEU by listening to the recording posted at  

Questions and Answers from Gut-Microbiota-Brain Axis Webinar from July 27, 2017:

How viable are the probiotic supplements that are in liquid form, in glass bottles, and refrigerated? Food scientists and manufacturers work very hard to test and create optimal storage conditions so that the consumer receives a food product with viable probiotics. My recommendation is to store the items as recommended and toss it when it expires to ensure the viability of the probiotics. Supplements are not always as stringently tested, so look for USP certifications and only buy supplements from reputable sources and stores.

Are fibrous foods the best sources of butyrate? Butryate is primarily a by-product of microbial fermentation of fiber. So, yes, consuming foods that contain fermentable fibers will provide the greatest boost in colonic microbiota production of butyrate. However, butter and milk fat also contains butyrate. The small bolus of butyrate released from butter digestion will also provide a source of butyrate directly from the diet and independent of microbial fermentation.

How do you measure short chain fatty acids (SCFA)? SCFA are analyzed using gas chromatography.

When did the importance of the gut-microbiota-brain become known? Are current dietetic students being taught this? a: Some of the early research, although it’s likely that the importance was noted early, occurred in the early 1900s. Dr. Illya Mechnikov noted that the Bulgarians were living significantly longer than those in many other countries. He proposed that the fermented milk they were drinking was contributing to their longevity. Over the last 5 years, this research area has exploded because of the funding and results of the Human Microbiome Project. The advances in sequencing technologies have revolutionized our understanding of the microbiome.  The use of germ-free animals is also helping us to better understand these complex relationships between the gut-microbiota-brain axis. b: Dietetic students do learn some of these topics through courses at the University of Illinois. I incorporate lectures on the microbiota in my Nutritional Aspects of Disease course, which is required for dietetics students. I also teach a Diet and the GI Microbiota graduate level course that undergraduate students in Dietetics (and other majors) can enroll in as well.

Is this the definition of fiber used for food labels? Not currently, but it will be very soon. The original change to the new food label was set for this summer, however, because FDA is currently reviewing some fibers for inclusion, the updated food labeling and use of the new fiber definition to categorize fiber in the foods has been delayed.  I anticipate that we should have more clarity on this topic before the end of this year.

I would love to see that plant-based/ animal-based study redone without so much processing of the animal-based foods.  For instance, serve grass-fed steak, or goats milk, or cage-free eggs etc. I agree that a study utilizing less processed meats would provide additional valuable information about the impact of a meat-based diet on the microbiota as we can appreciate that the levels of sodium and nitrates would have also been very high in those processed meats as compared to steak. In my opinion, the most important take home message from this study is that what we eat can very rapidly (within a couple of days) change the composition of the microbiota. This means that we should continue to encourage consumption of foods rich in fiber, like vegetables, whole grains, nuts, legumes, and fruits to support a diverse gut microbiota.

What would a source of agave inulin be? Agave is a plant that primarily grows in Mexico and the inulin from the agave plant is a byproduct that is collected while the plant is being used to make tequila. Some parts of the agave plant may be safe to eat and thus would provide a source of agave inulin. In the US and in the US food market, chicory inulin is the most commonly supplemented inulin. Chicory inulin also supports a bloom in Bifidobacterium. Inulin-type fructans are naturally found in a number of foods including, artichokes, asparagus, bananas, garlic, onions, leeks, and wheat.

What about the cellulose that is added to white bread? Cellulose added to bread will help contribute to a laxative effect and/or help with regularity. In general, cellulose is not fermented by microbes in the human gut.

Does the United States Pharmacopeia (USP) certify these supplements? Some supplements will have USP certifications.

Do you recommend food sources or supplements for prebiotics? In general, consuming whole foods is superior because you get the benefits of the fibers and the other phytonutrients in the food. My recommendation is to consume a diet that is rich in different types and amounts of vegetables, fruits, legumes, nuts, and whole grains, which will provide a variety of different types and amounts of fiber, which can, in turn, help support a more diverse and health gut microbiota. However, some prebiotics, like polydextrose and soluble corn fiber, are synthesized.  So, if you are trying to consume those specific fibers you would need to find foods that have those fibers supplemented, like muffin or pancake mixes or specific supplements. Again, I encourage you to only consider purchasing supplements if they are from a reputable source.

Do the probiotics in yogurt survive pasteurization? No, they generally do not survive pasteurization. However, food manufacturers will add back in the live and active cultures after pasteurization. Look for the “live and active” phrase on the side of the container to confirm.

Is there a recommended amount of yogurt or kefir per day to achieve a measurable amount of probiotic benefits? This will depend on the yogurt or kefir and the desired health outcome. In the studies presented today, 250 g/day or ~8 oz. per day for 4 weeks helped reduced stress in women. This probiotic guide provides some great information about the efficacy of different probiotics for different diseases/conditions:

Do you recommend Kombucha as a probiotic drink? I recommend caution when making your own fermented beverages because pathogenic bacteria can get into these homebrewed beverages. However, if you’d like to make your own, you can pasteurize it at home prior to consumption by heating it to at least 161F for > 15 seconds. With regard to products available in the grocery store, I’m not familiar with any research indicating that they are beneficial (or detrimental) to human health.  Those that are immunocompromised, the very young, and elderly individuals should also be cautious about consuming these beverages.

Can you provide feedback about why probiotics tend to be contraindicated in critical care settings? This probiotic guide provides some great information about the efficacy of different probiotics for different diseases/conditions:

Do you recommend taking probiotics and prebiotics when taking antibiotics?  Yes, some probiotics have been shown to help reduce antibiotic-associated diarrhea. See this guide for more information:

When would it be indicated that a probiotic supplement would be more beneficial than eating yogurt? The beneficial effect of consuming a probiotic will be related to the specific strain that is consumed. For example, some strains have been shown to be effective for constipation while others help boost your immune response. So, you should match the probiotic to the desired outcome.  Unfortunately, not all probiotics will be found in yogurt.  So, if you are just trying to support overall general health, consumption of a yogurt may be better than consuming a supplement because the yogurt will also provide other nutrients like calcium, which helps support bone health.  This probiotic guide provides some great information about the efficacy of different probiotics for different diseases/conditions:

Do you know of any studies that measured impact of fermented vegetables (kimchee, natto, sauerkraut, etc.) on gut microbiota? No, I’m not familiar with any.

Can too much probiotic food sources/supplements have harmful effects? Yes, too much of anything can be harmful. Probiotics may be contraindicated for those that are immunocompromised or in critical care.

Do you have any thoughts on the FODMAP (Fermentable Oligo-, Di-, Mono-saccharides, and Polyols) diet? This diet eliminates many short chain carbohydrates for a period of time for those with IBS. The FODMAP diet can be a useful dietary approach for those with IBS that are sensitive to gas and bloating. I recommend working with a Registered Dietitian to try to titrate back in as many foods as possible so that the diet is not lacking in the phytonutrients, vitamins, and minerals that are also present in some of the foods that are excluded when the FODMAP diet is implemented.


Let’s keep up the conversation!  Please share your thoughts on this topic or any other questions or resources you have found valuable in your practice!

This blog was posted by Robin Allen, a member of the Military Families Learning Network (MFLN) Nutrition and Wellness team that aims to support the development of professionals working with military families.  Find out more about the MFLN Nutrition and Wellness concentration on our website on Facebookon Twitterand LinkedIn.


Leave a Reply

Your email address will not be published. Required fields are marked *