What happens in your microbiome affects the brain
When Dr. Mayer started his career, he studied “how the brain talks to the gut” — the bi-directional interactions that affect irritable bowel syndrome (IBS). For decades, “this was the only entity that was considered a brain-gut microbiome disorder.” (The microbiome represents trillions of bacteria that live in our large intestine. They help our bodies break down fiber and provide us with nutrients and metabolites that are critical for health — and, we are learning, are also connected to the brain and immune system.)
When he expanded into the space of manipulating the microbiome with “a probiotic consortium of microorganisms, [we found that] we were able to change systems within the brain.” The study subjects were healthy, so “we can’t say if this had any potential therapeutic effects, but it did affect systems in the brain that have to do with threat appraisal and salience assessment.”
As a result, this field grew to explore the ways in which the microbiome-brain interactions affect mental health issues and neurodegenerative diseases like Alzheimer’s, Parkinson’s, depression, anxiety, and other developmental disorders. “Initially, the mistake was made to assume that this is a causal relationship,” Dr. Mayer explains. “We’re still inching closer to that point where we can say that an altered microbiome is clearly a risk factor for developing Parkinson’s disease. The final proof still has to be determined.”
A plant-based diet has benefits across the body
The question is: what components of a plant-based diet transmit a health benefit? “One is clearly the large variety of different molecules that’s contained if you are on a diet that is high in a variety of different plants, fruits, and vegetables,” says Dr. Mayer. These molecules are too large to be digested in the small intestine, so they go down to the large intestine where they’re broken down by the microbes, providing both a benefit for microbial health and ecosystem diversity. Another benefit is that these molecules also get broken down into substances that get absorbed “into our systemic circulation and exert health benefits on most of our organs from the immune system, systems in the gut, and all the way to the liver and the brain.”
Avoid hidden sugars; eat a diversity of fresh foods
“If you want to do something simple, straightforward: minimize sugar,” says Dr. Mayer. This means, looking beyond the sugar you might add to your morning coffee to the hidden sugars like high fructose corn syrup in products like ketchup. Another example is chocolate. “Certainly chocolate by itself is not such a bad thing because cacao is a very health-promoting substance,” explains Dr. Mayer. But all the sugar added to “bring it up to the taste preference of people in the U.S.” is what makes it unhealthy. “Hidden sugars are really abundant in our diet and it’s not by coincidence,” notes Dr. Mayer, mentioning that high fructose corn syrup is subsidized by the government.
“Hidden sugars are really abundant in our diet and it’s not by coincidence,”
Gluten is another ingredient in ultra-processed foods that was not as much a part of our diet 75 years ago. Unless you have celiac disease, “you could argue that gluten itself is not bad for you,” says Dr. Mayer. “But if you get it in excessive amounts together with all the other chemicals that are being added to this food, then it is bad for your gut health and gut microbial health.”
So what should you be eating? A recent study from Stanford compared people who ate a high-fiber diet with those eating a diet high in naturally fermented foods like pickles, kefir and other yogurts, and kombucha. The study showed that those eating a variety of fermented foods “had a greater benefit in terms of their gut microbial diversity and abundances,” says Dr. Mayer. “So you wouldn’t get this [benefit] with probiotic pills — it’s the variety of these different food components that probably convey the health benefits.”
The best diet is being aware of what you eat
Fad diets go back and forth between high fat and low fat. “First, there was the Atkins diet and then came the keto diet,” says Dr. Mayer. “It’s being promoted as the ultimate fat-burning diet.” You will lose weight on keto if you’re also working out, “but it’s not something you want to be on for the long-term because you don’t want to starve your microbes with all the negative downstream effects.” These microbes produce the anti-inflammatory molecules in your gut like short-chain fatty acids. “You don’t want to take away this medicine your body [has] to fight inflammation.”
“In general, if you eat what’s best for your microbial health and the health of your microbial ecosystem, it will automatically be the best for your gut health and for your overall health.”
Instead of these diets, Dr. Mayer recommends you simply pay attention to what you eat. “In general, if you eat what’s best for your microbial health and the health of your microbial ecosystem,” he says, “it will automatically be the best for your gut health and for your overall health.”
Time-restricted eating is one way to eat that has known benefits. Every 90 minutes, your gut contracts to reestablish the normal microbial abundances. But “if you eat and snack all day long, that pattern will be disturbed,” Dr. Mayer explains. “A lot of people get excited about cleansing diets,” but this is your body’s natural cleansing mechanism. “The best cleansing diet is actually this time-restricted eating.”
“The best cleansing diet is actually this time-restricted eating.”
Dr. Mayer recommends a 16-8 schedule where you keep your gut empty for 16 hours. If you have dinner at 7pm, your first meal would be the next day around noon. (You can calculate this from the time it takes you to digest your dinner — a light dinner, for example, will be cleared from your stomach and the small intestine in about an hour.) “If you’re busy in the morning on Zoom calls, you don’t even notice it,” he says.
There is no scientific study on what your first meal should be, but Dr. Mayer recommends lots of high-caloric nutrients that can be found in flax, sunflower, pumpkin, and chia seeds. These are “plant-based oils and fats, so it’s not harmful,” he says.
You can turn your diet around later in life and still make an impact
The goal of healthy longevity is one where we live longer and feel healthy. Dr. Mayer grew up in a family of confectioners. “I overdosed on sugary foods for the first 20 years of my life until I moved away and went to medical school,” he says. “Other than the damage to my teeth, I don’t believe there was any carryover from that early programming.” He notes several studies that look at working towards disease-free longevity starting at 50. What’s shown is that lifestyle modifications that include not smoking, regular moderate exercise, a healthy state of mind, and a healthy diet, “regardless of how you lived the first part of your life, have a major health benefit.”
“Lifestyle modifications that include not smoking, regular moderate exercise, a healthy state of mind, and a healthy diet, ‘regardless of how you lived the first part of your life,’ have a major health benefit.”
“There was this concept that the microbiome is programmed in the first three years of your life and then you’re stuck with it,” says Dr. Mayer. But we now know that within the bandwidth of a healthy microbial diversity, we have the ability to move from the bottom of that bandwidth, all the way to the top. This “gives us advantages in terms of healthy longevity.”