How Your Gut Microbes Can Keep Your Brain Young
Your gut microbes may help to prevent cognitive decline.
Posted Sep 28, 2020
“As you get older, three things happen: The first is your memory goes, and I can’t remember the other two.” — Norman Wisdom
That quote is funny, but for many people, aging is not a joke. Cognitive abilities begin to slip; memories start to fade. For some, depression darkens their closing years. Shockingly, much of that trend can be traced to an unexpected source: gut microbes. How can such tiny creatures milling around in the gut have such an impact on our minds?
The story goes back to your birthday. The original one, not the one you celebrate by blowing microbes onto a communal cake. When you were born, you picked up microbes from your mom. If you were a C-section, you picked up microbes from a hospital room. If you were breastfed, your mother gifted you with a starter immune system and bacterial sampler in her milk. In any case, most healthy babies end up with a belly full of Lactobacillus and Bifidobacteria, which you might recognize as the starring microbes in yogurt.
This personal collection of microbes is called the microbiota. The composition of our microbiota changes every day, depending on what we eat. When we first start eating solid food, our microbes shift dramatically. By the time we are one thousand days old, we have a resilient and distinctive microbiota reflecting all of the unique circumstances of our lives.
As we get older, our microbiota slowly evolves. There is a core set, some two-thirds, that stays fairly constant. But the numbers of certain species, especially Bifidobacteria, start to ebb. That may be a problem.
What goes on in the gut
The gut has a challenging job. It is supposed to allow nutrients to pass through yet keep toxins and pathogens at bay. It’s a porous barrier a single-cell thick, oddly tough for such a sheer membrane. It can be damaged, though. Stress and infection can cause the gut to become leaky enough to allow toxins and microbes into the bloodstream. The heart then obligingly pumps them to every tissue in the body. That means microbes can make it to the brain in seconds.
The brain has its own barrier and is careful to keep microbes out. But aging and stress can make that barrier leaky too, leading to “inflammaging” in the brain.
The invasion by pathogens or toxins is bad enough, but the body’s reaction may be worse. When the immune system counterattacks, there is plenty of collateral damage. Immune cells are not subtle. If they target a microbe inside a nerve cell, they may kill the cell along with the microbe. Memories are stored in nerve networks and killing nerve cells can take a toll on memory and cognition. That can lead to dementia: A leaky brain barrier may be an early harbinger of Alzheimer’s.
Microbes sound bad
This is how microbial incursions—and the resulting inflammation—can cause cognitive decline with age. In this bleak scenario, microbes are the bad guys. But this is biology we’re talking about, where simple scenarios are improbable. In fact, our gut microbes are far more likely to be wearing the white hats. The microbes in your gut are good for many things, including extracting the last bit of energy from your food. But their most important task is defending us against those black-hatted pathogens.
Before our immune system even becomes aware of pathogens, our good microbes will harass them, starve them, kill them, and shove them out. Our gut microbiota is the first line of defense against nature’s tiniest predators. A diverse microbiota prevents a few bully species from dominating the gut and causing disease. But as we age, our microbiota loses its variety. Our youthful helpers are diminished, and with our defenses depleted, we become frail.
As we age, we form habits, many of them bad. We tend to favor the same foods, day after day. We stay up late, bingeing into the wee hours and then wondering why we’re sleepy the next morning. For many, a sedentary lifestyle is a lifegoal. All of these behaviors lead to a subpar microbiota, ultimately sapping the wits out of us.
What can you do?
You need to turn off the TV, get off the sofa, go for a walk, and eat your vegetables. This is good, stern advice, and if you're anything like me, you've spent a lifetime looking for a loophole.
But in the light of the microbiota, there are a few new twists. The gut microbiota is malleable and can be rejuvenated in just a few days with a proper diet. Since a healthy gut is related to a diverse population of microbes and they each have their own cravings, you need to eat a wide assortment of foods. Variety isn't just the spice of life; it's essential.
Fiber, found in fruit and vegetables, is manna for your microbes. The top foods for fiber include artichokes, asparagus, onions, garlic, broccoli, beans, lentils, strawberries, raspberries, and blackberries.
Exercise, even in small amounts, can help to maintain a balanced and robust microbiota. You may think you’re too old for that, but it’s never too late. Once you start putting on a little muscle you will reclaim some youthful vigor and revel in your enhanced mobility.
That’s easy to say
The second day of a diet is usually the easiest because that’s when you ditch it. Sticking with the program is notoriously tricky, especially when it goes against your lifelong habits. So, how do you develop better habits?
It may be easier than you think. Scientists at the University of Warwick have created some compelling simulations suggesting that habits can be formed merely by repetition. Even if you hate broccoli, if you keep trying to eat it, you will eventually get into the groove.
The best part though is that you should feel better and better as your microbiota improves. Soon, you may actually crave broccoli.
The future of better guts
Using these insights, you can extend your health-span and improve the quality of your life. But there may be even more in store in the near future. A study by Robert Bryan and colleagues at Baylor College in Texas took fecal matter from old mice and young mice and transplanted each into young germ-free mice. Those that got the old feces acted depressed, had impaired short-term memory and impaired spatial memory for at least three months after the transplant. They conclude that old feces alone is sufficient to produce cognitive decline. This is an important result, demonstrating causality, not just correlation.
Are you ready for a youthful fecal transplant? If that doesn’t sound appealing, just wait. We should soon figure out the secret of fecal transplants. Purified and put in a capsule, it will be like any other probiotic, but one with the right stuff to reverse the declining quality of the aging microbiota.
In the end
We are all fermenting. We can let ourselves go sour like vinegar. Or, we can be thoughtful vintners and produce a classic wine. These microbial insights are a game-changer. Our golden years don’t have to involve mental decline. If we take care of our gut, we can keep our wits until the end. With diligence, your next birthday could be better than the last.
Dinan, Timothy G., and John F. Cryan. “Gut Instincts: Microbiota as a Key Regulator of Brain Development, Ageing and Neurodegeneration.” The Journal of Physiology 595, no. 2 (January 15, 2017): 489–503.
Montagne, Axel, Samuel R. Barnes, Melanie D. Sweeney, Matthew R. Halliday, Abhay P. Sagare, Zhen Zhao, Arthur W. Toga, et al. “Blood-Brain Barrier Breakdown in the Aging Human Hippocampus.” Neuron 85, no. 2 (January 21, 2015): 296–302.
Miller, Kevin J., Amitai Shenhav, and Elliot A. Ludvig. “Habits without Values.” Psychological Review 126, no. 2 (2019): 292–311.
Lee, Juneyoung, Venugopal R. Venna, David J. Durgan, Huanan Shi, Jacob Hudobenko, Nagireddy Putluri, Joseph Petrosino, Louise D. McCullough, and Robert M. Bryan. “Young versus Aged Microbiota Transplants to Germ-Free Mice: Increased Short-Chain Fatty Acids and Improved Cognitive Performance.” Gut Microbes 0, no. 0 (September 8, 2020): 1–14.