Sugar, Health, and the Microbiome: A Conversation with Dr. Emeran Mayer

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Dr. Emeran Mayer is a Professor in the Departments of Medicine, Physiology and Psychiatry at the David Geffen School of Medicine at UCLA, Executive Director of the G Oppenheimer Center for Neurobiology of Stress and Resilience, and Co-director of the CURE: Digestive Diseases Research Center at UCLA

Dr. Mayer is a world renowned gastroenterologist and neuroscientist with 35 years of experience in the study of clinical and neurobiological aspects of how the digestive system and the nervous system interact in health and disease. His current research focus is on the role of the gut microbiota brain interactions in emotion regulation, chronic visceral pain, and in obesity. 

His new book, The Mind Gut Connection, explores the biological link between mind and the digestive system.

Dr. Mayer is a SSEW Initiative researcher and was a memorable keynote at our 2015 SSEW Symposium: Gut Feelings (see his keynote talk here).  We asked him to comment on how the gut may play a role in food and addiction and what new research is cooking in his lab. Our conversation is below for your enjoyment! 

SSEW: They say you are what you eat and, generally, the standard American diet is full of sugar, food additives, and processed food. How does consumption of sugar and processed food impact our microbiome and what does this mean for the health of our minds, brains, and guts?  

Dr. Mayer: The simple answer is that during evolution our gut and its microbiome has never encountered anything like the onslaught of the standard American diet. This means that the system is not adapted to it, which results in dysregulation of the metabolism and brain function.  Regardless of the dietary component (excessive animal fat, sugar, emulsifiers, artificial sweeteners), one common denominator of this dysregulation is the development of low grade immune activation (“metabolic toxemia”), starting in the gut but spreading throughout the organism, including brain, heart and liver.


SSEW: Recent findings from UCSF researchers reveal that since the 1970s, skewed science has led to the national endorsement of a low-fat, high-sugar and high-carbohydrate diet. We are now witnessing the impact of these recommendations on the nation’s health in the form of the obesity and diabetes epidemics. Your research shows that processed foods and sugar impact the microbiome. What needs to happen on the individual and policy level in order to shape our environment into one that will support microbiome health?  

Dr. Mayer: In addition to the detrimental effects of components of processed foods and high sugar, there is extensive evidence that the intake of high animal fat (high in saturated fatty acids) and high amounts of red meat and energy drinks (containing high amounts of carnitin) can have negative health effects, and that these negative effects are mediated in part by the gut microbiome.  Based on our growing understanding of the gut microbiome, and excellent epidemiological studies, there is no question that diets consumed in moderate amounts,  high in plant based foods, including fermented foods, plant oils and whole grain, and fish, but low in red meat and animal fats are most beneficial for our overall health.  Such diets exist in different traditional cultural settings (Asian, European) are associated with high diversity and abundance of the gut microbiome, which currently is considered the best measure of gut microbiome health.  In my opinion a major educational and policy effort is necessary to teach the health benefits and the preparation of such diets as the Mediterranean diet, and not leave it up to bestselling authors to promote fad diets unsupported by scientific evidence.


SSEW: The theme of our 8th Annual SSEW Symposium was Food and Addiction. In your last interview with SSEW, you discussed how the microbes in our gut can talk to us, influence our mood, decision making, and even relationships. Do you think that microbiobes play a role in developing or sustaining addictions to certain foods?

Dr. Mayer: Based on some studies in mice it is plausible that gut microbes and their metabolites are able to influence the brain’s reward system:  fecal transplants from genetically modified overeating mice into lean mice was shown to make the recipient an overeating mouse as well.  Also, food preferences following gastric bypass surgery change rapidly and this is accompanied by a change in the gut microbiome.


SSEW: Many people would confess to having a sweet tooth. How might those common urges travel down into the microbiome or be driven by gut bacteria?

Dr. Mayer: Hard to say, but unlikely.  If anything, the gut microbes prefer complex carbohydrates which they can ferment, and not refined sugars.


SSEW: Is there a safe type or amount of sugar for your microbiome?

Dr. Mayer: Gut microbes to my opinion are not specialized to consume sugar, the great majority of which is absorbed in the small intestine and doesn't get into the large intestine where mostmicrobes reside.



SSEW: Some people find it hard to resist environmental cues that come in the form of food advertisements, packages specifically designed to market high sugar or processed foods to adults and children, and sugary beverages. We know that unhealthy environments increase the risk for obesity and metabolic disease.  How do you think the brain-gut connection is playing a role in this and what does the science say? 

Dr. Mayer: We all have hardwired craving for foods with high caloric density, which has been adaptive during evolution when sugar and fat were difficult to come by.   Advertisement builds on these inborn cravings and amplifies them on a daily basis.  High fat, high sugary foods (so called comfort foods) just like other addictive substances make us feel good temporarily, and this is conveyed in the advertisements.  However, the regular intake of these foods inactivates elaborate control mechanisms within the brain gut axis, leading to unrestrained intake.


SSEW: Our initiative aims to get researchers and policy makers working together to put an end to obesity and sugar related metabolic disease. What do think policy makers need to know about the micro biome to support individuals in cultivating optimal gut health and to create environments that support gut health?  

Dr. Mayer: They should promote simple guidelines to consume diets of moderate size, high in plant based foods, low in animal products (high in saturated fatty acids) and with minimal or no amounts of added sugars. The reduction in animal products not only reduces the amount of excessive animal fats (high in saturated FA), but also minimizes the intake of low dose antibiotics that are associated with current animal farming practices.The rationale for such diets is that they are associated with maximal diversity and abundance of the gut microbiota, which in turn is likely beneficial for the human host.


SSEW: Are there any exciting new studies or publications from your UCLA Lab that you share with SSEW? 

Dr. Mayer: We have several papers in press that demonstrate correlations of gut microbial architecture with brain signatures.  Most excitingly, we are currently in the process of analyzing large data sets of patients who have either undergone cognitive behavioral therapy or mindfulness based stress reduction.  We have collected stool samples for gut microbial and metabolomics analyses from these subject before and after therapy.

Interested in learning more about Dr. Mayer's research and his new book? Last year, former SSEW Initiative Executive Director Amanda Gilbert and Dr. Mayer talked about the brain/gut connection, and the effect of stress on this pathway. 

For more from Dr. Mayer, please visit his website at