Emeran Mayer, M.D., is a professor of medicine at UCLA and one of the world's leading experts on the relationship between the microbiome and the brain. In this adapted excerpt from his new book, The Mind-Gut Connection: How the Hidden Conversation Within Our Bodies Impacts Our Mood, Our Choices, and Our Overall Health (Harper Wave), Dr. Mayer explains how to optimize your microbiome for total health.
As we rapidly untangle the complex chemical conversations between microbes, the gut, and the nervous system, we're also extracting valuable information about how to apply this knowledge to improve people's health.
Down the road, if we could assess a person's gut microbial landscape and signaling molecules generated in this system, we could determine his or her vulnerability to antibiotics, stress, diet, and other destabilizing factors and design personalized treatments. Microbiologists and CEOs of startup companies are already busy mining the human gut microbiome for novel therapies, using new computational tools. But this may prove more difficult than they think.
In the meantime, there are approaches that anyone can take today without spending a lot of money. In a recent Science article, Jonas Schluter and Kevin Foster of the University of Oxford propose that we act as "ecosystem engineers" and manipulate general, system-wide properties of microbial communities to our benefit.
How can we do this? Here are the best research-backed ways to improve your microbiome for overall health:
1. Practice natural farming of your gut microbiome.
Think of your gut microbiome as a farm and your microbiota as your own personal farm animals. Then decide what to feed them to optimize their diversity, stability, and health.
Would you feed them food items that you knew were loaded with potentially harmful chemicals or enriched with unhealthy additives? This will be the first step in taking control of what you eat. It will increase your awareness next time you go to the market, are tempted to buy fast food for lunch, or debate whether you should order a dessert.
2. Cut down on animal fat in your diet.
All the animal fat in the typical North American diet, regardless of whether it is visible or hidden in many processed foods, is bad for your health. It plays a major role in increasing your waistline, and recent data has shown that processed meat, which has a particularly high fat content, enhances your risk of developing several types of malignancies, including cancers of the breast, colon, and prostate.
High animal-fat intake is also bad for your brain health. There is growing evidence that dietary fat–induced changes in gut microbial signaling to the brain via the gut's immune system can change our nervous system both functionally and structurally. Since our brain–gut axis has not evolved to cope with a daily avalanche of fat and corn syrup, and a high-fat diet sets up a vicious cycle of dysregulated eating behavior that harms your brain health, you should become aware of these unhealthy consequences.
3. Maximize your gut microbial diversity.
If you want to maximize your gut microbial diversity and reduce your vulnerability to chronic diseases of the brain, follow the old advice of nutritionists, cardiologists, and public health officials: In addition to eating moderate quantities of meats low in fat, mainly from fish and poultry, increase your intake of food items that contain multiple prebiotics in the form of different plant fibers, a combination of food items that we know today leads to greater gut microbial diversity.
Remember that your gut has evolved an elaborate system to handle a huge variety of naturally grown vegetables, fruits, and other plant-derived foods, as well as smaller amounts of animal protein—but that it struggles to handle all the fat, sugar, and additives that the food industry adds to processed foods. Unless you have been diagnosed with potentially serious medical disorders, try to avoid extreme diets that limit the natural variety of foods. Develop your own personalized diet within the general constraints of the "ground rules" of high-diversity foods, mainly from plant sources.
4. Avoid processed foods and maximize organically grown food.
Follow the advice that Michael Pollan gives in his recent book, Food Rules. Buy only things in the market that look like food. If they don't, they most likely will contain food additives that could harm your brain, including artificial sweeteners, emulsifiers, fructose corn syrup, and vital gluten, to name just a few.
For the same reasons, watch out for the hidden dangers in food you buy in the supermarket. Read labels to find out the components and additives in a food item; try to find out where it comes from. If you do this regularly, you will often be surprised that your fish or poultry comes from a country without rules for how these animals are raised and what they are fed, and how many calories are in a bag of so-called reduced-fat chips.
5. Eat fermented foods and probiotics.
While the science is still evolving, maximize your regular intake of fermented food products and all types of probiotics to maintain gut microbial diversity, especially during times of stress, antibiotic intake, and old age.
All fermented foods contain probiotics—live microorganisms with potential health benefits—and a few commercially available probiotics contained in fermented milk products, drinks, or in pill form have been evaluated for their health benefits. Unfortunately, there are also hundreds of such products, whose producers make vague claims of health benefits. Yet for many of them, we don't even know if enough live organisms reach your small and large intestine to exert their claimed beneficial effects.
But people have been eating naturally fermented, unpasteurized foods for thousands of years, and you might want to include some of them in your regular diet. Such products include kimchi, sauerkraut, kombucha, and miso, to name just a few. Various fermented milk products, including kefir, different types of yogurts, and hundreds of different cheeses, provide probiotics as well.
6. Fast to starve your gut microbes.
Periodic fasting has been an integral part of many cultures, religions, and healing traditions for thousands of years, and prolonged fasting may have a positive impact on brain functions and well-being.
A popular explanation for the benefits of fasting is based on the idea that it cleanses the gut and the body by getting rid of harmful and toxic substances. Even though people have believed this throughout history, there is little scientific evidence for this hypothesis. But based on what we now know about brain–gut microbiota interactions, fasting may have a profound effect on the composition and function of your gut microbiome and possibly on your brain.
For example, fasting may reset the many sensory mechanisms in the gut that are essential for gut–brain communication. These include our main appetite control mechanisms, which sense satiety. Having no fat in the intestine for one or more days may enable vagal nerve endings to regain their sensitivity to appetite-reducing hormones such as cholecystokinin or leptin, and it may also return sensitivity settings in the hypothalamus to normal levels.
7. Don't eat when you're stressed, angry, or sad.
We've seen that emotions can have a profound effect on the gut and the microbial environment in the form of gut reactions. A negative emotional state will throw the gut–microbiota–brain axis out of balance in several ways. It makes your gut leakier, it activates your gut-based immune system, and it triggers endocrine cells in the gut wall to release signaling molecules such as the stress hormone norepinephrine and serotonin. It can also reduce important members of your gut microbial communities. These can profoundly change the behavior of gut microbes.
For all these reasons, no matter how conscientious you are when selecting your food at Whole Foods, and no matter how much you believe in the health benefits of the latest fad diet, feelings of stress, anger, sadness, or anxiety always turn up at your dinner table. They can not only ruin the meal; if you eat when you're feeling bad, it can also be bad for your gut and bad for your brain.
For these reasons, scan your body and mind and tune in to your emotions before you sit down to eat something. If you are stressed, anxious, or angry, try to avoid adding food to the turmoil in your gut.
8. Enjoy meals together.
Just as negative emotions are bad for your gut–microbe–brain axis, happiness, joy, and a feeling of connectedness are probably good. If you eat when you're happy, your brain sends signals to your gut that you can think of as special ingredients that spice up your meal and please your microbes. I suspect that happy microbes will in turn produce a different set of metabolites that benefit your brain.
As noted by the authors of several scientific articles about the Mediterranean diet, some of the health benefits you get from eating a Mediterranean diet are likely to come from the close social interactions and lifestyle common in countries adhering to such a diet. The resulting sense of connectedness and well-being almost certainly affects the gut and influences how your gut microbiota respond to what you eat.