How is it possible for anything to influence so many systems of your body? The reasons are complex. But let’s start with some basic facts about probiotics.
1. Probiotics are bacteria and yeasts that live primarily in your intestines and are good for you.
2. You have a lot of them. If you were able to pull them all out of your body, you would have about a quart of bacteria and yeasts, and it would weigh almost three pounds — more than your heart, kidneys, and pancreas combined.
3. Probiotics are usually much smaller than our own cells, but we have ten times as many. Your body is made up of about 10 trillion cells. But you have about 100 trillion microbes living in and on your body.
4. Without that quart of probiotics, you would be unhealthy. To function properly, your immune system relies on those bacteria and yeasts.
The study on mice fascinated me. It reminded me of an earlier study done with humans showing that people who took probiotic supplements felt less stressed and had less anxiety and depression than people who had taken a placebo.
In the more recent study, researchers took normal mice, which are usually fairly timid (staying close to walls when they explore, and being reluctant to walk in the open). They fed half the mice a brew containing a particular strain of gut bacteria — Lactobacillus rhamnosus (a strain found in some yogurts and probiotic supplements) — and the mice became less timid; they explored more freely.
And when the researchers put the mice under stress (by plunging them in water, for example), the “probiotic mice” were less stressed than normal mice (the stress hormones in their blood didn’t rise as much in response to the stress). You can read more details about the study here and here.
But the researchers wondered how a bacteria in the gut could alter the mice “psychologically.” So they cut the vagus nerve — the bundle of nerve fibers that connect the guts and the brain — and sure enough, this stopped the positive effects of the probiotics.
So somehow the bacteria did something to the mice guts that sent a signal to the brain, causing the mice to feel (or at least behave) less anxious and depressed, and to produce less stress hormones.
The pathways for the other positive effects of probiotics — on allergies, heart disease, etc. — are at least as complex. For example, you have several kinds of white blood cells. One kind either calms down an inflammatory reaction in the body or inflames it. For the most part, it is in your intestines where these cells learn which kind of cell they should become.
In other words, depending on what they encounter in your intestines, they will become calmers or inflamers. If you have probiotic bacteria (rather than the bad kind), more of those white blood cells become calmers, and they then circulate in your bloodstream and prevent immune system overreactions like chronic inflammation to the inside of your arteries, for example, or rheumatoid arthritis, allergies, asthma, etc.
I don’t want to get too bogged down in technicalities here. If you’d like to know more detail about how the immune system works and how probiotics play a crucial part, I highly recommend a book by Gary Huffnagle, PhD: Probiotics Revolution.
Huffnagle is one of the leading probiotic researchers making new discoveries in this burgeoning field of research. He and a colleague were the first to create human-like allergies in mice using antibiotics. They were trying to answer the question: Why do more and more people have allergies and asthma in the last fifty years? If you look at the statistics, it looks like a rapidly growing epidemic. What’s going on?
Researchers discovered that the trend coincides with the use of antibiotics, which began to be used widely in the 1950’s, and there are many good reasons to suspect that antibiotic use and the rise of allergies and asthma are directly related.
As you probably know, when you take antibiotics, they kill harmful bacteria, but they also kill beneficial bacteria (probiotics). After you’re done with a round of antibiotics, your intestines will slowly try to come back to their former balance, but in our pasteurized, sterilized world, this is more difficult than it used to be. And besides, antibiotics don’t kill everything. They hardly affect yeast, which is usually only about one percent of our intestinal microbe population. But with its bacterial competition out of the way because of the antibiotics, yeasts can flourish. They and unfriendly bacteria more resistant to antibiotics can establish themselves, making it difficult for your intestinal flora (bacteria and yeast) to return to normal, even though there are usually plenty of bacteria and yeast in the air, which lands on our food and we eat it (this is how probiotics naturally wind up in our guts once we are no longer breastfeeding).
But the more rounds of antibiotics we endure, the more out of balance our intestinal ecosystem can become, and this lack of microbial balance can create problems — problems that can be solved by deliberately re-introducing beneficial bacteria (probiotics) into your diet.
There are several other things that contribute to an imbalance in our bacteria. Most important (besides antibiotics) is what we eat. Sugar selectively feeds harmful bacteria. Fiber selectively feeds beneficial bacteria. So as our diet has changed, the kinds of bacteria living in our guts have changed too.
We also aren't exposed to as many bacteria as we once were because of chlorine in our drinking water, antibacterial soaps and hand gels, etc.
This means if you want to have a healthy microflora, you're going to have to take deliberate steps to make it happen.
first do no harm
If you have a problem and you suspect probiotics may help, one of the best things about trying probiotics is that it can't hurt. If you eat probiotic-rich foods like yogurt and kefir and sauerkraut and it has no effect on your problem, you have not harmed yourself in any way. So it is certainly worth a try.
One of the immediate side effects of probiotics (and the only downside) is gas. The bacteria eat carbohydrates and fiber, and when they do, they produce hydrogen and methane. Gas.
The good news is that there are also bacteria that feed on hydrogen and methane! So if you continue to eat probiotics, after a few weeks the gas problem will disappear because the number of gas-eating bacteria rises until they are eating all the gas you are producing.
And speaking of feeding the bacteria, the other part of increasing the number of good bacteria in your intestines is to eat the right foods. Certain foods (like sugar, white flour, and white rice) selectively feed bad bacteria, while other foods, like beans, whole grains, and fruit, selectively feed probiotic bacteria.
So to give your probiotics a chance to flourish in your guts, you should not only eat foods containing probiotic bacteria, you should also eat PREbiotic foods (food that contains the kind of stuff probiotic microorganisms like to eat). I’ll have a list of both kinds of foods later in this article.
But first, here are a few interesting facts about probiotics:
1. Almost all the microbes in our intestines are bacteria, and there are many different kinds: Somewhere between 500 and 1000 separate species.
2. Most bacteria we are exposed to are either good for us or neutral. Very few bacteria are actually bad for us.
3. All living creatures have bacteria living in them. This includes fish, insects, birds and mammals.
4. Bacteria live in water everywhere on earth, and in dirt. There are over a hundred million bacteria living in a single teaspoon of rich soil.
5. Probiotic bacteria can digest fiber. Harmful bacteria typically cannot.
6. Some kinds of harmful bacteria and yeasts thrive on sugar.
7. One of the ways probiotics help is by competing with bad bacteria. For example, the bacteria that cause cavities (Streptococcus mutans) and gum disease (Porphyromonas gingivalis) are kept low by eating probiotic foods. The same is true with the bacterium that causes stomach ulcers (Helicobacter pylori). When you eat probiotic food, the beneficial bacteria compete with harmful bacteria and keep them from getting the upper hand.
8. Probiotic bacteria are so important, breast milk contains probiotics and prebiotics.
Probiotics are an important factor to consider in your diet. The number of studies on probiotics worldwide has exploded in the last fifteen years, and the things researchers are discovering are nothing less than revolutionary.
One interesting possibility, for example, is that the epidemic of obesity may have some relationship with gut bacteria. In one of the many experiments done with probiotics, obese adults reduced their food intake by 500 calories a day. Half of them included yogurt in their diet (six ounces three times a day) and the other half ate a different dessert with no probiotics but with the same number of calories.
Twelve weeks later, they were all tested, and all had lost weight.
But the yogurt eaters lost thirty percent more weight.
Coming from a different angle, the livestock industry has found that if they add a low dose of antibiotics in the feed (keeping the number of microbes in the livestock's intestines low), the animals gain significantly more weight on the same amount of feed.
Whatever your reason for interest in probiotics, it is worth the experiment to try raising the number of beneficial bacteria you eat and see what happens. With that in mind, below are two lists; one is a list of foods containing live probiotic bacteria, and one is a list of prebiotics — foods that selectively feed probiotic bacteria already in your guts.
top probiotic foods
1. Yogurt. This is the most well-known probiotic food, and the one that first awakened scientists to the possibilities of probiotics’ potential. A Nobel Prize-winning immunologist, Ilya Mechnikov studied the famously long-lived peasants of Bulgaria in the early 1900’s and discovered that there was something unique about their diet, which he attributed to their longevity: They ate a lot of fermented food, including yogurt.
There are many different kinds of yogurts, and they contain different combinations of bacteria. Each kind of bacteria may be important, so your best bet is to eat different kinds of yogurt regularly. Also make sure the yogurt you choose has “live, active cultures” because some yogurt makers ferment milk into yogurt with bacteria but then pasteurize it (heat it up to kill the bacteria), which defeats the probiotic purpose of yogurt.
And one other thing: Try not to eat sugary yogurt. If you want some sweetness and flavor, see how little sweetness you can get by with. Just add fruit without sweetener or buy the sweet kind but also buy plain (unsweetened) yogurt and mix them.
2. Kefir. This is a cultured milk that tastes somewhat like a liquid yogurt, but with a great many more different kinds of bacteria than yogurt, and also containing some yeasts. It is easily made at home (and it will cost a lot less if you do). Learn more about kefir here and here.
3. Sauerkraut and kimchi. Both of these are fermented cabbage. Kimchi has the added flavor of other vegetables and spices. But with these products, you must find versions with live, active cultures. Usually these will be in the refrigerated section of a health food store. You can also make your own inexpensively. Learn about that here.
4. Fermented pickles and tomatoes. Also in the refrigerated section.
Sometimes fresh live cultured foods can be expensive. To find out how to make probiotic foods at home for less, I heartily recommend the book, Wild Fermentation.
top prebiotic foods
Below is a list of foods that have substances in them that selectively feed probiotic bacteria and simultaneously help to starve harmful bacteria in your guts:
7. Whole oats
9. Whole wheat
11. Red wine
Caring for your own intestinal ecosystem could benefit you in many ways. I believe that we're only just scratching the surface so far. But there is no reason to wait until all the results are in. Healthy people have been eating probiotic and prebiotic foods for a very long time with no negative side effects, and probably gaining many benefits along the way. You can start your own experiment with your guts right away and see just how healthy you can become.
In the book, Probiotics Revolution is a list of which bacteria have been shown to benefit which ailments. And also a good list of which supplements are the most reliable.
Adam Khan is the author of Principles For Personal Growth, Slotralogy, Antivirus For Your Mind, and co-author with Klassy Evans of How to Change the Way You Look at Things (in Plain English). Follow his podcast, The Adam Bomb.