Dr. Gerard Mullin on Prebiotics for Gut Health, Weight Gain from Antibiotics, and More

The gut microbiome is a dynamic living ecosystem made up of 100 trillion microbes in the intestinal tract. This complex system of viruses, bacteria, and fungi protects against foreign pathogens, helps regulate the immune system and control inflammation, and may even affect your mood — among its many other functions. We sat down to speak with Dr. Gerard Mullin, an associate professor of medicine at The Johns Hopkins Hospital and author of the book The Gut Balance Revolution, about all things related to gut microbiome health. Read on to learn the risks of weight gain from antibiotics, the benefits of probiotics and prebiotics for gut health, the best yogurt for gut health, and more. 

*This is a short clip from our interview with Dr. Gerard Mullin. Click here to watch the whole thing.*

You can also listen to our interview with Dr. Mullin on The WellBe Podcast. 

Learning Early About the Importance of Gut Health

When Dr. Mullin was growing up, his mother suffered from irritable bowel syndrome. At the time, conventional medicine was extremely dismissive of the condition, believing that it was a hormone-driven psychiatric disease of hysteria in middle-aged women — in other words, that it was all in her head. His mother was told to deal with emotional stress in her life, or work with a psychiatrist, in order to heal her digestive issues.

Unsurprisingly, this wasn’t a satisfying answer for Dr. Mullin’s mother, and so she took matters into her own hands, finding a solution through what we would today call “integrative medicine” but which didn’t have a name at the time. She did reduce stress in her life, but her main focus was diet. She experimented with different foods and food groups, and settled on a diet that turned out to be incredibly healing for her gut. “She found her own solution in what today we would call the ‘gut microbiome,’” says Dr. Mullin. “Now, that was back in the 1970s, and that was really inspiring for me. Eventually, it led me to go to medical school so that I could help others with similar conditions.”

Watching his mother also inspired Dr. Mullin to address his own health issues. Growing up, he struggled with his weight, and after he saw his mother’s success, he began adjusting his own diet. He changed his diet and lifestyle in similar ways to her, optimizing his microbiome without really realizing that was what he was doing, and lost over 120 pounds in the process.

The Serious Risk of Weight Gain from Antibiotics

As Dr. Mullin’s personal experience showed him, the gut plays an important role in your weight. So, since antibiotics have such a massive impact on your gut health, it makes sense that antibiotics would also impact a person’s weight. To illustrate the relationship between the two, Dr. Mullin brought up two powerful studies, both conducted by Dr. Martin Blaser, which show the potential extent of weight gain from antibiotics.

In the first study, Dr. Blaser was able to induce obesity in mice simply by giving them sub-therapeutic levels of antibiotics — levels equivalent to the amount you would get from eating meat from antibiotic-fed animals twice per week. As Dr. Mullin explains, “that amount of antibiotic that’s in the meat, it remains in the meat. When we ingest it, we absorb the antibiotic, and it’s enough in us to cause obesity.”

Dr. Blaser’s other landmark study looked at veterans who had been treated for the stomach bug known as H. pylori. He theorized that after being treated with antibiotics for H. pylori, the vets would experience weight gain from antibiotics — and the results confirmed this theory. After taking antibiotics, the subjects saw an increase in ghrelin, the appetite-stimulating hormone, as well as an increase in overall weight and BMI. Dr. Mullin notes that these results are of particular importance given the fact that, although only 5% of the population in the United States have H. pylori, throughout the rest of the world, that rate is 50%, so awareness of antibiotic overuse is a global risk. 

Dr. Mullin expresses particular concern on how overprescription of antibiotics might be impacting children. “There’s a lot of data on children who are getting antibiotics for viral infections and otitis media [ear infections]. There’s more and more data linking not only obesity, but also Crohn’s disease and other autoimmune diseases, to early onset antibiotics in proportional doses,” he says. “That’s when the microbiome is being laid down, and immunity is being laid down — the first two years of life — so you start messing around with that, the consequences downstream can be unfortunately bad.”

The Benefits of Probiotics and Prebiotics for Gut Health

If antibiotics are so bad for gut health, it follows logically that their opposite, probiotics, would be good for gut health. They’re also helped out by prebiotics, a different but equally important factor in optimizing the microbiome. To fully understand the role of probiotics and prebiotics for gut health, Dr. Mullin says that it’s essential to understand that the gut microbiome is a dynamic, living ecosystem within us. 

“When we eat, we eat not only to provide calories for us and micronutrients, and other essentials for our cellular health and our overall health, but we’re also feeding our microbiome as well,” he says. “When we eat, somehow, we have to keep that in mind. We need to feed another organism within us, because that organism will, in turn, support our health and our growth. It’s like a state of pseudo-pregnancy. ” This means that it’s essential to incorporate probiotics and prebiotics into your diet.

Probiotics are living bacteria that can be found in certain food and drink, as well as in supplement form. They are commensal in nature, meaning that they consume the food eaten by their host, aka you, and they, in turn, help you build a robust and diverse microbiome that supports your overall health. 

Prebiotics similarly support your microbiome, but rather than being live bacteria, they are the food substances that the bacteria eat. Dr. Mullin explains that prebiotics are foods that we cannot ferment on our own, but that the good bacteria in our guts can ferment, helping to support the growth of more friendly flora within us. You can take prebiotics for gut health in supplement form, but Dr. Mullin recommends getting your prebiotics via food. For the most part, prebiotics are found in fiber that humans can’t digest but that their bacteria can. Asparagus, bananas, and artichokes are all examples of prebiotic-containing foods. 

For a list of the best probiotic- and prebiotic-containing foods, as well as effective and fully vetted prebiotic supplements, download our free gut health guide

The Best Yogurt for Gut Health 

One food that’s commonly cited as being good for your microbiome is yogurt. In yogurt ads and on packaging, you’ll see claims like “contains live cultures” and “probiotic,” which position yogurt as a great choice for gut health. But according to Dr. Mullin, not all yogurt is created equal, and many yogurts don’t really do anything for your gut. 

He explains that most yogurt you’ll find in the store contains no or very little bioactivity, or live bacteria. This is because most yogurt manufacturers use pasteurization, which involves heat treatment that kills the bacteria. At the end of the process, some yogurt makers will add back in some live bacteria, but nowhere near as much. 

He also points out that many yogurt brains contain tons of added sugars and flavors, which have their own negative repercussions for the microbiome. “What you’re getting is a lot of sugar and a lot of added stuff, which makes it enjoyable and pleasurable to eat,” he says. “But no one really looks at the impact of flavored, sugar-filled yogurt on the microbiome.”

So, the best yogurt for gut health is yogurt that you make at home. Dr. Mullin explains that homemade yogurt will generally contain over 100 billion CFUs, or colony-forming units, per serving; store-bought yogurt, on the other hand, usually has only three to four billion units per serving, at best.

Of course, most of us don’t have time to make our own yogurt at home. When it comes to store-bought products, Dr. Mullin says that the best yogurt for gut health is actually kefir, which is a drinkable fermented milk with high levels of bacteria. Because there’s been no research on whether or not flavored kefirs have microbiome benefits, Dr. Mullin recommends buying plain kefir, and then flavoring it yourself with vanilla, stevia, fresh berries, cinnamon, or whatever other flavors you desire (fresh berries offer you a double gut health benefit, since berries are a prebiotic complement to the probiotics in the kefir). 

If you don’t have easy access to the best yogurt for gut health and need a quick snack, it won’t do any harm to your gut to choose a regular, mass produced yogurt (though we would definitely recommend going organic and checking sugar content). “If you really want to be serious about repopulating your microbiome, having some commercial-grade yogurt is better than having ice cream, but it’s suboptimal,” says Dr. Mullin.

Do you take prebiotic or probiotic supplements? Which ones? Let us know in the comments below!

Watch our full video with Dr. Mullin to learn why medical school curriculum focuses so little on nutrition and whether he sees that changing, how to know if you’re eating enough probiotics or prebiotics to optimize your microbiome, how artificial sweeteners impact the gut microbiome, why goat and sheep dairy is a better choice than cow dairy, the challenges and benefits of eating fish, and much more. 

You can also listen to our interview with Dr. Mullin on The WellBe Podcast. 


The information contained in this article comes from our interview with Dr. Gerry Mullin, MD, a medical doctor board-certified in internal medicine, gastroenterology, functional medicine, and nutrition. He is an associate professor of medicine at The Johns Hopkins Hospital in Baltimore, as well as the co-founder of the JHH Nurse Practitioner Fellowship Program. He is a founding member of the American Board of Integrative Medicine and serves on the editorial board of numerous journals for gastroenterology, nutrition and integrative medicine. He has more than 20 years of clinical experience in the field of integrative gastroenterology.  His qualifications and training include a doctorate from UMDNJ-New Jersey Medical School, and a residency at Mount Sinai Hospital. You can read more about Dr. Mullin here.



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