Gut bacteria contribute to your mood, your waistline, your overall health, and even the size of your nads. Here's how to make sure you have the right balance.
You Are 90% Non-Human
Your body is comprised of approximately 10 trillion human cells. But you also harbor approximately 100 trillion bacterial cells. Do the math. You're 90% non-human.
There are far more bacteria in your body than there are people on earth. There are even more bacteria in your body than there are stars in the Milky Way. Together, the bacteria in your body represent roughly 3000 species, with a collective pool of 3 million distinct genes. Compare that with the paltry 19,000 genes or so that make up the human body.
Not only do these bacteria play a big part in regulating your digestive system and your immune system, but even your emotions, the way you think, your body fat levels, and perhaps even the size of your testicles.
What We Learned From Wet Mice
Neuroscientist John Cryan conducted a very weird experiment. He took mice and divided them into two groups. One was the control group and the other group was fed lactobacillus ramnosis, a bacterium often used to make generic yogurt.
After a couple of weeks, he threw all the mice into bowls of water to see how they'd react to water stress. Now rodents are very good swimmers, but they absolutely hate water; it freaks them out. The control group tried frantically to get out of the bowl. Their efforts continued for four minutes until they became exhausted and gave up. It's what's known as "behavioral despair."
But the bacteria-fed mice? They too tried to get out, but their efforts were far less frantic. They continued swimming around the bowl past the four-minute barrier of the control group. Finally, at six minutes, Cryan pulled the soggy rodents out.
You're no doubt thinking the yogurt somehow conferred extra endurance to the test group, right? Wrong. What Cryan found was that the levels of stress hormones were 100-fold higher in the control group. All that panic isn't good. You burn out and shut down after a couple of minutes, as was the case with the mice in the control group.
The lactobacillus mice, however, had half as much stress hormone flowing through their mousy veins. Additionally, they exhibited a profound change in the distribution of their GABA receptors into a pattern associated with calm, non-depressed animals. GABA acts pretty much the opposite of stress hormones. It makes you chill out so that when you're thrown in a bowl of water, you don't panic – you don't reach the point of behavioral despair. As such, the lacto mice acted as if they were on Valium, or maybe gotten hold of some really primo indica.
So how was it possible that bacteria in the mice's guts were somehow having a calming effect on the mice's brains? Cryan asked that same question so he duplicated the experiment, but this time, before placing the lacto mice in the water, he severed their vagus nerve, which is the big cranial nerve that meanders from the abdomen to the brain.
The swimming lacto mice with the severed nerve acted just like the control mice! Frantic paddling. Behavioral despair. Cries of "Help me, you bastard!" They gave up at roughly four minutes. In fact, all beneficial responses were absent.
The conclusion is that somehow, a colony of lactobacillus bacteria living in the guts of the long-swimming mice had somehow chemically tweaked their vagus nerve, sending a signal to the brain to release the calming chemical GABA.
But does it have any carryover to humans? Can bacteria actually affect the neurochemistry of humans, change the way we think and react to stress and who knows what else? The short answer is, yeah, it looks like it.
Forget Prozac, Pass the Kim-Chi
A study similar to Cryan's was conducted in France, albeit with humans and the absence of any water sports. Test subjects were fed massive amounts of two probiotics, lactobacillus and bifidobacillus.
After a couple of weeks, standardized psychological surveys indicated that the subjects were less stressed, less anxious, and less depressed. These results were confirmed with assays of their 24-hour cortisol levels.
The theory is that the strains of bacteria produced an inordinate amount of serotonin, which is a calming chemical that often rises, for instance, after you eat high-carb foods. In truth, the human brain normally contains a very small amount of serotonin, while 80% of your serotonin supply is found in the gut, so it shouldn't be a stretch to think that bacteria aren't influencing the supply.
The results of these experiments, along with others, has led the National Academy of Sciences to actually start wondering if they could treat psychological disorders not with drugs, but with "medicinal" yogurt. But "mind control" is just the tip of the fermented chunk of cheese of biological processes influenced by bacteria.
Probiotics vs. Pathogens
Everybody knows the role bacteria play in digestion, how they help break down complex carbohydrates and help retain nitrogen from the breakdown of proteins and how a lot of your poop is just dead or dying bacteria, but I don't want to focus on that stuff. Instead, let's explore the less well-known attributes of these strange organisms.
For instance, it's believed that the "good" bacteria, the probiotics, are involved in a constant life and death struggle with pathogens. They do this by damaging or killing these pathogens, sometimes by secreting chemicals, sometimes by changing the pH of the environment, or sometimes by just crowding them out.
These good bacteria also produce, as byproducts of their metabolism, nutrients key to our immune system like certain B vitamins and vitamin K. In fact, probiotics are thought to comprise about 70% of our immune system. Even the appendix – once thought to be a vestigial organ – seems to be a repository of probiotics, releasing them as needed during infections.
Many diseases that plague us might simply be caused by dysbiosis, an imbalance between probiotics and pathogens. There are the obvious ones like irritable bowel syndrome (IBS) and Crohn's disease, but other, less suspect diseases like cardiovascular disease and diabetes might also be caused or exacerbated by dysbiosis. Dysbiosis might be related to just about any autoimmune disease you can think of, from asthma and arthritis to ulcerative colitis and vitiligo.
What happens is that an imbalance of bacteria, stress chemicals, or hormones causes the intestinal lining to become more permeable. This increased permeability might then allow invaders to enter your bloodstream where they alert the immune system and lead to localized or systemic inflammation.
The Bacteria Made Me Fat
There's also been a lot of research on the idea that bacteria might play a large part in actually determining body fat levels. Gastric bypass surgery, largely thought to be effective purely because of physics, i.e., a smaller stomach leads to fewer calories being ingested, but as much as 20% of the weight-loss effect may simply be from a subsequent shift of the balance of bacteria in the gut.
Mice subjected to bypass surgery lost weight, as expected, but when scientists transplanted the intestinal contents of the bypass mice to control mice, the control mice rapidly lost weight, too. The same procedure could well work with humans.
Another study involving 792 subjects found that overweight people might harbor a certain type of bacteria that may contribute to weight gain by helping other organisms in their environment digest certain nutrients, thereby making more calories available. They theorize that this type of bacteria might have been useful to humans thousands of years ago when roughage played a much bigger role in the diet and it was essential that every possible calorie be squeezed out of the available food.
Scientists also suspect that an imbalance of gut bacteria can increase insulin resistance and adipocyte fat storage by suppressing something called FIAF (fasting-induced adipocyte factor).
Yes, They Can Even Contribute to the Size of Your Balls
Studies on the relationship between bacteria and obesity even led to the puzzling but welcome observation that mice fed a vanilla-flavored yogurt grew substantially larger testicles, so much so that they walked with a "swagger" not unlike John Wayne.
Two groups of mice were involved, one fed a junk food diet plus yogurt, and one fed a healthy diet plus yogurt. The junk food eaters experienced a 15% increase in testicular size while the healthy eaters only experienced a 5% increase (the junk food eaters had smaller balls to begin with, hence the disparity in percentages).
The healthy diet plus yogurt eaters also inseminated faster and produced more offspring. Lastly, they also grew shiny coats and had 10 times the "follicular density" of normal, un-yogurted mice, making them look like tiny, white-haired Alec Baldwins.
Would it also apply to human types? It seems it might. Harvard nutritional epidemiologist Jorge Chavarro has found that ingesting yogurt improves the semen quality in human males.
Don't Like Germs? You'd Best Stay in the Womb
The first and last time you were ever sterile – completely free of bacteria – was in the womb. But then, as you were rudely ushered out into the world through your mother's birth canal, you were simply inundated in bacteria. (Babies that are delivered by Caesarean miss out on this seemingly vital bacterial bath and as a result are thought to be more susceptible to certain allergies, eczema, and even obesity.)
You were then exposed to a world of microorganisms. In the subsequent weeks and months, you were handled by a bacteria laden mother and father, exposed to bacteria laden air, kissed by a bacteria laden aunt's lips, licked by a bacteria laden dog's tongue, and sucked on a bacteria laden carpet, all of which played a part in establishing your particular bacterial ecosystem, which, if you were lucky, was allowed to flourish.
If you weren't so lucky, you were maybe born to germophobic parents, exposed to several rounds of antibiotics, or, in general, assailed your natural bacterial population with years of antiseptic soaps, disinfectants, mouthwashes, chlorine pools, and various bacteria-killing prescription drugs.
In a manner of speaking, your bacterial ecosystem is the rainforest, and you've willfully introduced unfettered hordes of loggers, farmers, miners, industrialists, and poachers to run roughshod over your immune system and it's likely given you a severe case of dysbiosis. In that's the case, it's likely your bacterial population is out of whack.
Yogurt and Probiotics Aren't the Cure
Let's get one common misconception out of the way. Having a cup of yogurt every day isn't going to do much to repopulate your gut with the right bacteria. There are hundreds or thousands of species of bacteria in your gut and a typical yogurt probably contains two strains of bacteria.
However, if you insist on going the yogurt route, it's best to avoid brands that contain sugar as these supposedly feed competing bacteria. I'd also recommend avoiding any brands that are advertised on TV by women who make orgasm faces when they eat the yogurt. Instead, look for stuff made by shepherds using yak milk or something, stuff that may have been strained through burlap that has disgusting bacterial clumps in it. (And I'm only half kidding.)
And here's more disheartening news: taking probiotic supplements (pills, capsules, liquids) doesn't often work, either. No study has shown that supplemental probiotics become permanent residents.
Now before you throw the previously cited studies in my face, the one about the mind-controlling yogurt and the mice with bigger balls, it seems likely that particular strains of bacteria – given in high doses over a short period of time – can have medicinal effects, but that still doesn't mean they become permanent residents.
Part of the problem might have to do with the supplements themselves, which are often victims of mishandling. Capsules and tablets should be refrigerated, not just after you buy them, but also immediately after they were manufactured, during shipping, and at the store. And there's no way to tell if that actually occurred.
If you decide to go the pill or capsule route, make sure they at least conform to the following standards:
- The quantities of bacteria are listed in CFUs (colony forming units) and not milligrams.
- The product is, despite what the label says, refrigerated.
- The product is encapsulated with a protective medium such as oil, nutrient culture, shells, or coated tablets.
A Better Way: Fermentation
A better tactic is to eat foods that are both probiotic and prebiotic. These are fermented foods that contain beneficial bacteria and simultaneously feed them.
Granted, most of these fermented foods – like the aforementioned yogurt – depend heavily on the action of one or two microorganism (lactobacillus and bifodobacillus), which is only a small sampling of the microorganisms in a healthy gut, but it looks like they may create an environment conducive to the growth of other bacteria in the same way as a rising tide lifts all boats.
Even so, some experimentation is going to be in order to see which fermented foods work for you. Sample at least one of the foods in the following list every day. (Consider that one serving of sauerkraut has about the same amount of bacteria that you would hope to get in an entire bottle of capsulated probiotics).
- Kombucha (a culture of bacteria and yeasts brewed into a tea)
- Umeboshi (fermented, pickled plums from Japan)
- Tempeh (fermented soybeans)
- Pickles (only those marked "fermented")
Generally, these are foods that contain normally indigestible carbohydrates like inulin, fructooligosaccharides (FOS), and galactooligosaccharides (GOS). We can't digest these carbs, but the lactobacilli and bifidobacilli feed on them.
If you buy any of these foods, buy them only from the refrigerated section of the grocery store. Otherwise, there's a good possibility that most of the bacteria are inviable or dead. They of course have to be stored in the fridge when you get home, too.
You also have to refrain from heating them excessively. For example, plenty of people have an affinity for fried sauerkraut. Too bad frying makes in practically sterile.
Foods for Gut Bacteria Health
Foods like the following supply your new gut bacteria with the things they need to flourish, like FOS and inulin:
If these foods don't sound appetizing to you, buy yourself an oligofructose supplement and augment your diet with at least 5 grams a day (hopefully getting close to a total of 20 grams of prebiotics a day).
As far as GOS, it might even be more powerful of a prebiotic than FOS and inulin. It's lately getting a lot of interest from research groups that have shown it to reduce anxiety and depression in human subjects to a profound degree, both of which are thought to result from inflammation.
Foods rich in GOS include
- Green peas
- Lima beans
- Kidney beans
A daily half-cup serving of any of these foods should do the trick and keep your bacteria growing. Each of these foods contains about 6 to 7 grams of prebiotic fiber, of which about 3 to 4 grams is GOS.
What You Can Expect to Happen
So let's say you do all of this. You become a foster parent to trillions of new bacteria. How do you know that it's doing you any good?
In the short term, you might feel less flatulence, become more regular, experience less bloating in general, get better skin, and notice stools that are more "aerodynamic," or Shamu like.
Over the long term, it might help mitigate any autoimmune system problems you might have, including asthma, skin allergies, irritable bowel, arthritis, etc. It might very well make you more resistant to diseases, too.
- Brockman, John (editor), "This Book Will Make You Smarter," Harper Perennial, New York, 2012.
- Choi, Charles Q, "Probiotic Bacteria May Help Treat Depression," LiveScience website, Aug. 29, 2011.
- Dolgin, Elie, "Mice That Eat Yogurt Have Larger Testicles," Scientific American, Friday, May 4th, 2012.
- Grady, Denise, "Bacteria in the Intestines May Help Tip the Bathroom Scale, Studies Show," The New York Times, March 27th, 2013.
- Radiolab broadcast of "Guts," April 2nd, 2012.
- Roach, Mary, "Gulp: Adventures on the Alimentary Canal," W.W. Norton and Company, 2013.