You step on a scale and see a number there. It says, “You weigh this many kilos or pounds”.
This seems straightforward. But within that number, there are 1.5-2.5 kg (3-4 lbs) of mass which aren’t really you. This mass is all the bacteria that live on and inside your body, accounting for 2 to 3% of the total number you see on the scale. That’s about the weight of a full bottle of wine, made of pure bacteria, which you carry with you all day and night, every day of your life.
When you look around at all of our big buildings, fancy cars, and terraformed environments, it’s easy to think of humans as the peak of evolution. But if the contest wasn’t technological but one of numerical advantage, you’d have to say bacteria are the clear winners, accounting for the largest group of non-plant life on Earth. Mammals are just a tiny fraction of that, and humans are a tiny fraction of that fraction.
This graphic (from a study by the National Academy of Sciences) shows the distribution of biomass on earth, with the right slide zoomed to show how the sliver of animal mass is distributed. If you like this kind of thing, also check out this Vox article which has some well made graphics showing how small human biomass actually is.
To bacteria, we’re not an impressive big-brained higher species, we’re roving planets meant to be colonized. Bacteria begin this colonization as soon as you’re born.
Babies in the womb don’t have microbes or bacteria. They get their first dose when moving from the birth canal and then through their mother’s milk. Recent studies show that baby’s delivered through C-section miss out on vaginal bacterial exposure, a difference which can persist for the rest of their lives!
If you were to deconstruct your body and count the number of human cells vs. bacterial cells, you’d find there are 10 TIMES more bacterial cells than “you” cells. Who’s really hosting whom on this planet?
Also like a planet, we have different biomes located across our body. Some bacteria prefer the dry canyons between our skin cells, others prefer the moist swamp of the mouth, and many, many, MANY bacteria thrive in the dark, hot, acidic jungle that is our intestinal tract. These bacteria make up the gut biome, accounting for 80% of the bacteria in that afore-mentioned wine bottle.
Over the eons, humans and bacteria have evolved together. Our bodies learned through natural selection that we don’t have to do everything ourselves. Sometimes we can outsource a biological task to the microscopic hitchhikers living in our gut, saving ourselves precious energy to use for other parts of survival.
Here are just a few of the jobs our gut bacteria do for us:
- Bacteria are able to break down plant fiber and cellulose that would otherwise be indigestible. This aids digestion and lets us soak up vitamins and minerals that would pass right through without our little friends.
- Bacteria synthesize vitamin K, an important molecule for immune function and bone health.
- Bacteria neutralize and remove toxins that would otherwise make us sick.
- Bacteria guard their biome jealously and stop harmful microbes from taking up residence in our intestines.
This is all very real, very cool science, and most exciting of all, we’re just at the dawn of our understanding of how the gut biome interacts with our wellness. There are groundbreaking studies coming out every year, showing significant health outcomes from transplanting bacteria from healthy people to unwell individuals. Give a depressed person gut bacteria from an upbeat person, and they become less depressed. Give an obese person gut bacteria from a lean person, and they lose fat. Wild stuff, and it will just get better and better.
But, as with any breakthrough in health, there’s a trailing wave of pseudo-science looking to make some cash off of the buzz. Now that the idea of the gut biome has filtered down through the culture, we’re seeing marketers seize on it as a new selling point for a host of products. Vitamin stores and health food sections of the supermarket now have shelves devoted to prebiotic and probiotic supplements, promising health through boosting gut bacteria. Fermented foods like yogurt, kefir, sauerkraut, kim-chi, and kombucha are all leaning hard into how their live bacteria are part of keeping your gut flora balanced.
This leads us to today’s question. How do you promote a healthy gut biome? Do these foods and products work as advertised? Should you change what you eat for better gut health? Let’s cut through the hype and get some clarity on the issue.
We’ll start with probiotics.
Probiotics are foods, liquids, powders, or pills that contain live, “activated” bacteria. The pitch is that ingesting these bacteria will let them populate your gut and give you a healthy and balanced gut biome, better digestion, and an increased immune response.
Is this true?
Probiotics are the new Vitamins (meaning they don’t really work).
At Kenzai we’ve been trying to tamp down the hype for vitamins for over a decade. There’s no good scientific evidence that vitamins boost health for individuals with a healthy diet. Unless you’ve been diagnosed with a specific deficiency, or are in an unusual health situation such as being pregnant, the only thing vitamins just give you is expensive, colorful pee.
It turns out that probiotic supplements are following the same trajectory as vitamins. The best research to date shows that there’s no probiotic supplement “boost” to be gained for a healthy person with a normal gut-biome.
There are a few reasons probiotics aren't effective and don’t make sense for healthy people.
1. A healthy gut doesn’t have any vacancies.
Your gut bacteria have been passed on to you from your mother and your environment, and have been coexisting with you for your entire life. There’s no way a few grams of bacteria from a pill or probiotic food is going to change or dislodge the established bacterial colonies. This would be like planting a Sakura tree in the middle of the Amazon rainforest, and expecting to come back in a few years for cherry blossom viewing.
Your gut biome has evolved to fit you like a glove. Even if you could disrupt your bacteria with a supplement, you wouldn’t want to introduce such an invasive species into your carefully balanced system, and you wouldn't want to replace your robust and varied gut biome with a monoculture of store-bought bacteria.
2. Probiotics are almost always the wrong bacteria
There are trillions of species of bacteria, and no two people will share the same mixture of gut flora. At this point our understanding of gut bacteria and its function is so basic, we’re like Europeans in the 1500s theorizing what kind of animals might be living on the North American continent which had just been found a few years earlier.
Probiotic marketers will skip over the fact that they have very little idea whether the bacteria in their products are the bacteria you need, or, if those bacteria are even compatible with the human gut biome. One bacteria’s as good as another right? No, not really!
As a simple example, take the bacteria Lactobacillus, which is what turns milk into yogurt by converting sugar into acid (this is what gives yogurt its tartness). Humans also have Lactobacillus in the upper gut, so yogurt must help keep your gut well supplied with good bacteria right? The catch is Lactobacillus is the name of an entire family of bacteria. It could mean Lactobacillus crispatus, Lactobacillus jensenii, Lactobacillus rhamnosus, Lactobacillus plantarum, Lactobacillus casei, Lactobacillus reuteri, and on and on.
The Lactobacillus that makes yogurt is Lactobacillus acidophylis and Lactobacillus bulgaricus. This is not the Lactobacillus that lives in the human gut. The intestines are dark, hot, acidic, and low in oxygen. You can’t make yogurt with the Lactobacillus that lives in the gut, and you can’t populate the gut with Lactobacillus that makes yogurt! It’s been estimated that we’re unable to even culture in a lab 80% of the bacteria found within our bodies.
Very often, the bacteria that’s found in probiotic foods and supplements is there because it’s easy for manufacturers to culture and package, not because it’s what your body actually needs. And like vitamins, probiotics are unregulated, meaning that anything could be inside the product, regardless of what’s on the label.
3. Consuming billions of bacteria might make things worse.
Your gut flora have staked out their positions in your intestines and will be happily going through their life cycles and playing their part in your digestion. If you then start to bombard them with lots of probiotics for an extended period of time, you can create an inflammatory response in the intestines, as your native bacteria react to what they see as invaders. If you’ve ever had food poisoning you know what this looks and feels like at its extreme. Stomach pain, cramps, gas and diarrhea are how intestinal inflammation presents itself.
The irony of this is that many probiotic products promise better digestion, and some go so far as to boast that you’ll have a "cleansing event" after using them. That’s one way to describe diarrhea caused by bacterial inflammation of the gut!
This problem is more likely to be found in the products which really pack in the bacteria, and less so in traditional fermented food products with more mellow bacterial concentrations.
The bottom line — going out of your way to supplement with probiotic pills is a waste of money for a healthy person. There’s no high quality evidence that you can get any “boost” to digestion and immune-health through additional bacterial ingestion.
If you like fermented foods like yogurt, kimchi, sauerkraut, etc… then by all means eat them freely. But don’t go out of your way to over-emphasize them in your diet looking for a health benefit.
How about Prebiotics?
Next up is the vague term “prebiotics” which is quickly becoming the hot new buzzword in the health food section.
Prebiotics are foods or supplements that promise to feed existing gut bacteria. Essentially any high fiber food is a prebiotic. Prebiotic supplements are just powdered mixtures of fiber, no different than Grandma’s Metamucil fiber powder that has been out since the 1930s.
Look at all these slick graphics and modern colors! This isn’t your grandpa’s Metamucel! Except that it is.
We see many times with the body that powdered supplements are inferior to getting your nutrition the old fashioned way, as part of solid, minimally processed food sources. There’s no reason to think ingesting fiber from an expensive powder is more advantageous than getting it from a carrot, pear or leaf of spinach. Your body evolved in a world of fruits and vegetables, not of powders, and your bacteria love nothing more than chowing down on a half-chewed piece of plant material that’s made its way to your gut through a healthy diet.
In other words, the only prebiotics you need to stock up on are in the produce section, not the supplement aisle.
THIS is the real vitamin and supplement section of the supermarket! Believe it!
One thing we know for sure is that a diet of low-fiber processed foods and excess meat starves the gut bacteria and impairs gut health. If you want a healthy gut biome, a varied and nutritious diet is the single biggest intervention you can make. It’s more important by orders of magnitude compared to a probiotic or prebiotic supplement regimen.
So who needs probiotics?
Throughout this article we’ve been careful to use the phrase “if you’re healthy” when downplaying the need for bacterial supplements. However, there are situations when a person has an out-of-whack gut biome, where the native bacteria have been decimated due to exterior factors.
The most common cause of this situation is after taking antibiotics, which are as deadly to gut bacteria as to the infection you’re taking them for. Research shows that eating probiotic foods after an antibiotics treatment helps the gut return to normal balance faster with fewer complications. So probiotics do help to replace lost gut flora then? Isn’t that an argument that probiotics are all junk science?
Not so fast. The root of the gut improvement is more likely due to the inflammatory response that foreign bacteria create in the intestinal tract. Other studies have been done with non-food related bacteria and have shown the same results. After an antibiotic treatment, anything that prompts the remaining surviving native bacteria to rise up and defend themselves helps restore homeostasis faster. Researchers have gotten the same effect by flooding the systems of test animals with Candida, a fungal infection!
If you’re recovering from an antibiotic treatment, go ahead and eat some probiotic foods. But know that it’s not the bacteria from your plate that’s going to populate your gut, it’s more likely that bacteria is going to irritate your gut enough for the natives to recolonize lost ground.
Real gut health change is medical in nature
As we discussed at the start of this article, there’s compelling evidence that significant and lasting health benefits are possible when we target the gut biome with a medical dosage of bacteria from another human being. Fecal transplants are a promising example of this. The stool of a healthy person is taken, blended into a slurry, then implanted directly into the colon of the sick patient. THIS is what a true probiotic intervention looks like. It happens in a hospital with professional supervision and follow-up.
Drinking a bottle of kombucha every day or taking a sketchy, unregulated probiotic supplement is light years away from how gut health is actually improved.
Probiotics and prebiotics can safely be left on the shelf. Save your money for the things that friendly bacteria really crave — fresh fruits and vegetables in the context of a balanced diet.
Play a good host to your gut bacteria. Feed them well with the foods they love, and they’ll return the favor in thousands of ways we’re only just beginning to understand!
Patrick Reynolds // Kenzai Founder
Sources for this article:
Impacts of Gut Bacteria on Human Health and Diseases: International Journal of Molecular Sciences
Probiotics and Probiotics Revisited: Science Based Medicine
Do Probiotics Really Work?: Scientific American