What is your microbiome and why is it important?
Epistemic status: mostly well-established microbiome biology, with specific figures sourced below.
You may have noticed the incredible amount of attention the gut microbiome has received in magazines, newspapers, and medical literature — but what exactly is it, and what's the hype about?
The gut microbiome is a collection of trillions of microorganisms that live in the intestinal tract, with the greatest density residing in a pocket of the large intestine called the cecum. These organisms are mostly bacteria, but also include yeast, other fungi, and viruses.
Here's a fact worth knowing on its own: for years, it was widely repeated — in both popular media and scientific papers — that bacteria outnumber human cells in the body by about 10 to 1. A 2016 recalculation published in the journal Cell(Sender, Fuchs, and Milo) traced that number back to a rough 1970s estimate and corrected it: the actual ratio is close to 1 to 1. Still remarkable — you're carrying roughly as many microbial cells as human ones — just not the number most people have heard.
That density has real implications for how we think about ourselves. These organisms pass genetic information to us and secrete chemicals that interact with the rest of the body, with effects reaching further than most people expect: body composition, immune function, allergic tendencies, blood sugar response, and — an area still actively being researched, with much of the strongest evidence so far in animal studies — mood and cognitive function via the gut-brain axis.
The exact mechanisms aren't fully understood, but the diversity and density of the microbiome are consistently associated with better health outcomes. Diversity refers to how many different species are present — estimates of total possible species vary by study and sequencing method, but more diversity is generally protective, likely because a broad mix crowds out pathogenic organisms and gives you a network of organisms suited to different conditions (diet changes, illness, stress). It's the same logic diversification serves in an investment portfolio — spreading exposure so no single failure point takes down the whole system.
Four ways to support the diversity and density of your microbiome
Use antibiotics only when you need them. They don't treat viral infections, so talk with your doctor about whether treatment is appropriate. If you do need antibiotics for a bacterial infection, ask about pairing them with a validated probiotic. Skip antibacterial soap unless there's a specific reason for it, and where practical, choose meat raised without routine antibiotics.
Eat a wide variety of plant foods. The American Gut Project — one of the largest citizen-science microbiome studies to date — found that people eating 30+ different plant types per week had measurably more diverse microbiomes than those eating fewer than 10. Variety matters more than volume of any one food.
Give your gut a consistent overnight fasting window. Twelve hours between dinner and breakfast is a reasonable, low-risk starting point for most people. Longer or more structured fasting protocols can offer additional benefit for some people, but they're not appropriate for everyone — if you have a history of disordered eating, are pregnant, or have a diagnosed medical condition, talk to a doctor before extending beyond a basic overnight window.
Keep added sugar in check. The average U.S. adult consumes about 17 teaspoons of added sugar a day — roughly 60 pounds a year — according to CDC national dietary survey data (NHANES, 2017-2018). That's well above the American Heart Association's recommended limit of 6 teaspoons for women and 9 for men, and high added-sugar intake is well-documented to promote overgrowth of less beneficial microorganisms.
— Douglas Jaser