Human bodies are mysterious. They are full of wonders (brains, kidneys) and horrors (earwax). We spend our entire lives in these flesh sacks, and yet we don’t fully know how they work, or how jeans will fit them from one day to the next
And the gut microbiome might be one of the most bewildering corners.
Gut health has become something of a wellness buzzword. Part of this is due to legitimate advancements in the field of microbiome research, which has boomed over the past two decades thanks to advances in DNA sequencing methods. And part of it is due to social media hype and new products promising quick fixes to the stubborn problem of the human condition.
Among these products: at-home microbiome testing kits, which customers can order and use to take a stool sample and mail it for analysis. The company then sends back a report on the customer’s gut health along with dietary recommendations. According to a video Paris Hilton posted on Instagram, when she sent in her stool sample to Viome – a company that produces at-home testing kits and in which Hilton has invested – she learned that her “superfoods” include avocados and apples, but that she should avoid broccoli.
Thousands of TikTok and Instagram posts claim that these kits can help with conditions as varied as bloating, joint pain, anxiety and “leaky gut” – a nebulous term that encompasses ailments including bloating, diarrhea and low energy. According to the Mayo Clinic, it is a “hypothetical condition that’s not currently recognized as a medical diagnosis”.
Experts agree that the microbiome is important to human health. But many are skeptical about how useful these kits are – at least for the time being.
We asked experts about what the gut microbiome is, how it affects our health and whether at-home testing kits are actually any help.
What is a microbiome?
Microbiome is a general term used to refer to a community of microorganisms – organisms you can’t see without a microscope, such as bacteria, fungi and viruses – explains Dr Jonathan Eisen, professor and microbiologist at the University of California Davis.
We have microbiomes on our skin, in our mouths and in our reproductive systems. There are also ocean microbiomes, soil microbiomes and air microbiomes.
What is the gut microbiome?
The term “gut” refers to humans’ gastrointestinal tract – the organs that make up our digestive system. These include the stomach, large intestine and small intestine. These organs are full of trillions of microorganisms, which make up the gut microbiome. (Whether the gut microbiome itself qualifies as an organ is up for debate.)
What is a healthy gut, and how does the microbiome affect gut health?
There is no one definition of a healthy gut, says Dr Kira L Newman, clinical assistant professor of gastroenterology and hepatology at the University of Michigan.
Each person’s microbiome is different. And unlike, say, our genes, which are largely fixed throughout our lives, our microbiomes are ever-evolving, changing based on factors like age, nutrition, lifestyle and hormone changes. “It is horrifically complicated and unstable,” Eisen says.
In general, though, Newman describes a healthy gut as “one that allows for the digestion of food, absorption of nutrients, and elimination of waste”.
The microbiome also helps protect our bodies from bad bacteria, explains Dr Nicholas Ilot, senior researcher and lead bioinformatician for the Oxford Centre for Microbiome Studies. It does this in a number of ways. “Through occupying space in the gut, it acts as a blanket, creating a barrier between our gut tissue and any opportunistic invaders,” he says. The microorganisms in the microbiome can also compete for nutrients that certain harmful bacteria need to survive. And some of its bacteria produce molecules that can help our immune system.
How does the gut microbiome affect one’s health overall?
“It’s clear that the microbial community in the gut has a big impact on the health of mammals,” Eisen says.
But how the gut’s microbial balance affects specific health conditions is still largely unclear. Wellness influencers and companies selling at-home testing kits claim that learning the balance of your microbiome and making dietary adjustments accordingly can boost a person’s energy, improve their skin and help with anxiety.
But most of these claims are based on studies that identified correlations rather than causation, Eisen says, adding that many such studies were “probably not done in big enough populations to be convincing”.
Imbalances in the gut microbiome have indeed been associated with a range of chronic diseases, including gastrointestinal, inflammatory and metabolic conditions as well as neurological, cardiovascular and respiratory illnesses, says Dr Vijaya Surampudi, physician nutrition specialist at UCLA Health.
What is a gut microbiome test? Do I need one?
At-home microbiome testing kits range in price from $120 to $400. In addition to a gut health report that breaks down the types of bacteria and yeast present in your microbiome at the time you took your stool sample, many companies also provide personalized diet recommendations based on your results. Some also offer personalized probiotics to help correct supposed microbiome imbalances.
It’s hard to speak broadly about gut microbiome tests since the process is not standardized. “Every company uses a different methodology,” Surampudi explains. And these tests have not been scientifically validated for their utility in assessing gut health, she adds.
Usually, Surampudi says, the tests use DNA or RNA sequencing to evaluate the microorganisms present in a stool sample.
This process can take several weeks. By then, the balance of one’s microbiome may have shifted slightly. As Ilot notes, a microbiome test serves as a snapshot of your gut at a specific point in time, reflecting the food you had eaten in the days before. “Would it look the same tomorrow? Or in a week, a month?” he says. “It will look similar, but not exactly the same.”
Is leaky gut real?
On platforms like TikTok and Instagram, “leaky gut” gets tossed out as a potential reason for people’s gastrointestinal distress, brain fog and fatigue. According to the Mayo Clinic, the theory behind the hypothetical condition is that intestinal permeability is both a cause and symptom of gastrointestinal disease. If too much of the bacteria and nutrients from our gut gets through the walls of the intestine, the thinking goes, toxins could enter the bloodstream and cause inflammation.
“The ‘leaky gut’ hypothesis of how gut bacteria impact metabolic conditions and liver disease is an area of active research,” says Ilot, and there is still a lot we don’t know.
Gut permeability can vary in different states of health and disease, Newman says, but there is no technical definition of leaky gut. Besides, the gut is always supposed to be a little “leaky”, she explains, because the intestines naturally absorb water and nutrients.
So are at-home microbiome test kits effective or a scam?
Right now, microbiome tests are a useful diagnostic tool for a “limited number of conditions”, says Eisen. These include Crohn’s disease and type II diabetes.
But Newman says that, “at this time, there is no clinical use for direct-to-consumer microbiome tests”, adding that these tests are not reliable or regulated in the same way as FDA-approved lab tests.
With these at home kits, there is often high variability in results, she says. “A person could get two very different results from two separate companies, even if they sent the same sample.”
Identifying the species within the gut microbiome is fairly straightforward, says Dr Justin Sonnenburg, professor of microbiology and immunology at Stanford University, but drawing meaningful conclusions from this data is still difficult. Using these microbiome profiles to “recommend foods or predict disease is exceedingly difficult and only being done properly by a small number of groups”, he says.
But experts agree that while it is difficult to draw meaningful conclusions from people’s microbiome profiles right now, they could be a valuable tool in the future.
“[Microbiome tests] may be part of our clinical testing,” says Dr Surampudi. Possible uses might include assessing how a person responds to a particular medication or food. “But we’re not there yet.”