Food and Water Lunchtime Chats Webinar Nutrition

Q&A: Dr. Ryan Walker Answers Your Nutrition and Gut Microbiome Questions

The Gut and Microbiome Lunchtime Chat has generated many follow up questions. Gain in-depth insights on the impact of nutrition on gut health from a leading expert in the field.

A Gut and Microbiome Lunchtime Chat Webinar generated many follow up questions. Gain in-depth insights on the impact of nutrition on gut health from a leading expert in the field

A flurry of questions came in during the recent Lunchtime Chat webinar on nutrition and the gut microbiome with Ryan Walker, PhD, Assistant Professor of Environmental Medicine and Public Health at the Icahn School of Medicine at Mount Sinai. Here, Dr. Walker responds to those we couldn’t get to during the live webinar.

Ryan Walker, PhD

Is there a strong correlation between oral and gut microbiota such that oral samples could be used instead in human studies?

Although oral microbiota can translocate to the gut (and vice versa), they are distinctly different communities. Dysbiosis in oral and gut microbiota have been linked to some similar disease risks and some emerging work is using oral samples to predict disease risk, however they are typically studied independently to address unique scientific questions.

I have heard from some that it is good to have a dog in order help build greater immune systems but have also heard that pets introduce “bad bacteria” that could be harmful.  Can you please expand on this?

Exposure to household pets in early life has been shown by some to increase the richness (amount) and the diversity (types) of bacteria that comprise the human gut microbiome and these “traits” have been linked to improved immune function later in life. Other studies have found little to no effect. One group of researchers studied Amish individuals and found they suffer from less immune-related illness than others, which is potentially linked to early life exposure to farm animals. More work needs to be done to understand these complex relationships, but a majority of the literature suggests potential health benefits from pet exposures.

How does Xylitol impact the gut microbiome?

Xylitol is a naturally occurring polyol (sugar alcohol) carbohydrate found in many plants that has “sweet” taste properties. For this reason, it is often used in sugar-free candy as a sweetener substitute. It is not calorie-free, as many believe, but has been touted for its ability to reduce dental caries when replacing sugar in food products. Humans are mostly unable to digest or absorb xylitol, so it passes to our gut bacteria where it has prebiotic-like impacts. Gut bacteria metabolize xylitol and animal studies have shown that ingestion of xylitol can increase levels of acetate and propionate, which are short chain fatty acids (SCFAs) linked to several health benefits. Although xylitol has been linked to health benefits in humans, the overall mechanism is not fully understood.

Photo by Tembela Bohle:
Excess alcohol consumption has been linked to an increase in bacterial overgrowth.

How does alcohol affect the microbiome?

Excess alcohol consumption has been linked to an increase in bacterial overgrowth, dysbiosis of the microbiota and inflammation in the gut. Alcohol-induced bacterial overgrowth is thought to result in excess acetaldehyde (a metabolic product of alcohol metabolism) in the gut, which can trigger production of proinflammatory compounds, like endotoxins, in the gut. Occasional “social drinking” (i.e., 2 standard drinks) is not thought to have an impact on the microbiota.

Is breastfeeding enough to restore an infant’s gut health if they have been exposed to the NICU and a dose of antibiotics in the NICU?

The infant gut microbiome is very dynamic and quite susceptible to disruption from exposure to antibiotics and other possible environmental exposures that take place in a NICU environment. Babies born by C-section are more likely to be admitted to a NICU than babies born vaginally, and breastfeeding has been reported extensively to help in restoring the characteristic gut microbiome after a C-section delivery. Similarly, it is thought that breastfeeding is also beneficial in helping gut microbes recover from antibiotic exposure. However, more research is needed, and it is a difficult scientific question to study. The bottom line is breastfeeding is thought to be beneficial, in many ways, to the developing infant’s gut.

Do you know of any resources to support communities to develop healthier diets to support their microbiome, especially in culturally relevant ways?

Good nutrition is critical for maintaining a balanced and stable microbiome. High fiber, from fruits and vegetables, is probably the single best way to promote gut health. Good community nutrition and equitable access to healthy foods and food choices are one of the main public health challenges we face in our country, and we are doing a terrible job of addressing them (sadly). Any resource that assists in providing access to healthy foods, like fresh fruits and vegetables, which will also likely benefit your gut microbes. Unfortunately, there are not many of these resources available due to the structure of our food system in the USA.

What is know about the influence of the gut microbiota on neurodevelopment and behavior?

Gut microbiota are convincingly involved in the gut-brain axis (a bi-directional communication system between our guts and our brains). The microbiome has also been extensively shown to modulate risk for a variety of neuropsychiatric disorders as well as play a role during developmental windows early in life that may impact future behaviors. For a more comprehensive discussion of this topic, I recommend reading this recent review.

What are the effects of PFAS/PFOS on the human microbiome?

This is an area of increasing interest. There have been animal studies that demonstrate exposure to perfluorochemicals can alter the composition and diversity of the gut microbiota, promoting inflammation and dysbiosis that could be linked to disease risk. There are almost no studies in humans, however. Some very recent work has shown that PFAS exposure in infancy can alter the structure of the gut microbiome, but it is not known what direct health risks this may pose. PFAS exposure has been repeatedly linked to a myriad of poor health outcomes, and it is likely that alterations to the microbiota are involved, but these mechanisms are not yet understood.

What is the association between soil and the gut microbiome?

The absolute number of microorganisms in soil and our gut is quite similar, however the diversity of our gut microbiome pales in comparison to soil diversity. However, this microbial biodiversity in soil has been alarmingly decreasing with modern agricultural practices (pesticides, herbicides, agrochemicals). Given that many foods we consume grow in soil (or are exposed to soil microbes), it can be considered an exposure that influences our own microbiota. But lower soil biodiversity, coupled with increased processing of foods and excessive hygiene practices, is limiting our own exposure to the microbes in the soil. This has been proposed as a mechanism of reducing our own gut biodiversity, which is generally considered an unhealthy trend.

I am curious if you know of any research or data on the microbiome’s effect on auto-immune diseases or if probiotics have been shown to be beneficial in those with auto-immune diseases?

Differences in the microbiota in people with autoimmune diseases, compared to healthy individuals, have been observed. I encourage reading this recent review on the topic. Whether or not these observed changes are causally linked to disease remains under investigation. The use of probiotics has been shown to be beneficial in improving GI symptoms and general inflammation in some autoimmune diseases, but the mechanisms remain unknown. Typically, probiotics are thought to potentially reduce some symptoms of existing conditions, but are not (yet) considered sufficient to prevent disease onset.

Can you define artificial sweeteners?

Artificial sweeteners, or sugar substitutes, are generally any non-sugar sweetener added to foods to control “sweetness”. They typically are lower in calories than sugar, but retain sweet-taste properties. The FDA currently allows the following sugar substitutes to be used as additives: Acesulfame potassium, Advantame, Aspartame, Neotame, Saccharin, Sucralose , Luo han guo, purified stevia leaf extracts. Erythritol is a non-nutritive sugar alcohol sweetener that is approved as a food additive by the FDA. Research into the health effects of these compounds is ongoing and many have been shown to have detrimental effects on our microbiota, potentially enhancing disease risk.

Does fructose from fruit have any of the same effects as high fructose corn syrup from sodas? Should we limit fructose from fruit?

Fructose in fruit exists at a fraction of the concentrations seen in common sugar sweetened beverages. For example, an apple (a “high” fructose containing fruit) has ~13g of fructose whereas many typical sugar sweetened beverages contain up to 50g of fructose from high fructose corn syrup. HFCS and table sugar (sucrose) are both composed of glucose and fructose, however the fructose in HFCS is unbound to glucose and can exist in a higher proportion than in sucrose. This makes it easier to absorb quickly, so the “delivery” method is completely different. Our bodies have a limited ability to absorb dietary fructose and when we consume large amounts of it at once (i.e., via a soda) and I believe that this fructose in “malabsorbed”, passes to our colon where it can impact the microbiota. This process does not happen with fruits.

Our bodies have a limited ability to absorb dietary fructose and when we consume large amounts of it at once. Photo by Lukas, Pexels.

Do you think we are “too clean” nowadays? Especially in terms of washing hands, fruits, veggies, etc.

Modern-day changes to hygiene, agricultural practices, antibiotic use, and a shift to urban living have all been extensively linked to a decline in microbial diversity. This decline in microbial diversity is generally thought to be detrimental to our overall health, even though hygiene practices and antibiotics save thousands of lives daily. The COVID-19 pandemic, where sanitation practices soared to new extreme levels never seen before on a population-wide scale, has introduced more concern related to decreased microbial diversity in humans. I recommend this fascinating article that discusses this in more detail.

How can I test to see the “health” of my gut – does it require DNA sequencing as well as stool sampling? At what frequency should the stool sampling be done? Who interprets the results of such tests?

Stool is used as a “proxy” to study our gut microbiota. From this stool, bacterial DNA is isolated and software analyses are used to determine what species are present in the gut community. There are some private companies that offer stool microbiome analyses. Reporting of results is generally limited to showing how you compare (in terms of 1. the abundance of certain bacteria in your gut and 2. The overall diversity of the bacteria in your gut) to many other people in the population. There is scientific progress being made toward identifying bacterial “signatures” that predict disease, but these are not yet at the diagnostic level. A single sample analysis is sufficient to determine your overall community structure, which could suggest you may benefit from dietary changes for example. Additional samples are usually taken, in a research setting, to determine the effect of whatever you are studying (diet, exercise, drug, etc.) on the gut microbiome and range in frequency from daily to monthly to yearly depending on the question (and the budget!).

Have you studied the effect of certain spices such as turmeric, and cardamon on the gut microbiota?

There are mixed results on the role of spices and the microbiome, mostly from smaller studies that are not conclusive. Certainly, bioactive compounds and other metabolites (for example, plant phenols) in plants have the potential to interact with, and possibly modulate, our gut bacteria. But, to date, it remains unknown if and how this may occur.

What microbiome is most suitable or used for respiratory health research?

Typically, researchers that study respiratory health use sputum samples or bronchial gavage (a more involved procedure) to study the airway microbiota. There is some current work aiming to use exhaled air as a representative lung sample, but this is ongoing. Here is a great recent article on the lung microbiome.

Are the probiotics on the market adequate?

Probiotics have been shown to help improve symptoms of some diseases via potential changes to the gut microbiome. But, they are not generally thought to prevent (yet) disease from occurring.

What is the effect of the gut microbiome on appetite and food cravings?

Metabolites produced by gut bacteria can directly impact the production and secretion of appetite-regulating hormones in the gut and alter brain responses to hunger and satiety (eating behavior). It is a fascinating field of research. I recommend reading a more detailed review of the topic here.

What is known about recurrent GAS strep throat and overall microbiome?

To my knowledge, group A strep (GAS) can produce biofilms, which are specific communities of bacteria or mini-microbiomes. Very little is known about the role of these biofilms in GAS, but this is not my area of research.

Has there been research on children’s gut health with PICA (non-food) ingestion on gut health or negative consequences?

Typically, to my knowledge, geophagy (eating dirt) is a response to nutrient deficiency or to reduce sensations of hunger. Because the gut microbiota has been associated with, via the gut-brain axis, appetite regulation and eating behaviors it is possible there is a role for gut bacteria in geophagy, but I do not believe it has been formally studied.

Why is it so hard to convince policymakers of the importance of the gut microbiome on health outcomes and the need to make changes in the average American’s diet?

I don’t know the answer, but the second part of your question keeps me up at night. The National Institutes of Health (NIH) certainly recognize the importance of the gut microbiome in health and disease and continue to fund research to more clearly understand its role. Similarly, many within our government recognize the dire situation of our food system and our resultant poor collective diets as Americans. But, very little has been done to enact real, equitable change. This issue is deeply entrenched in the current political, economic and cultural trends in our country…food in America is an extremely complicated topic! Thankfully, the current administration is beginning to recognize the importance of nutrition in America. Check out this NPR article that gets into more detail.

Can you comment on any association between food allergies and the gut microbiome?

Mounting evidence supports a role of microbiota in food allergy risk. I’ll defer to my fellow Icahn Mount Sinai colleagues, who are experts in immunology and food allergy, to answer this. See a recent review paper they co-authored.

Is there a specific gut microbiota species that we must pay high attention as we age like how we watch our weight or blood pressure?

The most common change to the gut microbiome with age is a decrease in overall diversity. Very recent work has shown that as we get older our gut microbiome’s become more and more unique to us (i.e., sharing less common attributes with others). Additionally, a pattern of microbiota changes from aging, associated with healthy people, is a reduction in Bacteroides. So, increased “uniqueness” and decreasing Bacteroides are linked to “healthy” aging. But, there is not enough work to definitively (yet) say there is a specific species you need to track as you age.