Your gut is home to roughly 38 trillion bacteria, along with fungi, viruses, and other microscopic organisms.1 That might sound alarming, but most of them are helpful—or at least harmless. Together, they make up what scientists call your gut microbiota, and they do a lot more than you might expect. These tiny residents (collectively called your microbiome) help break down foods your body can’t digest on its own. They also teach your immune system what bugs to fight, make certain vitamins, and even send signals to your brain that affect your mood.
Here’s the part that surprises most people: a man’s microbiome looks meaningfully different from a woman’s. And those differences help explain why men are more likely to develop certain digestive problems. In fact, being a guy is one of the biggest factors shaping which bacteria live in your gut, right up there with what you eat and how old you are.
His Gut vs. Her Gut: A Tale of Two Microbiomes
For a long time, researchers treated the difference between male and female bodies as a side note when studying gut health. That changed when studies involving thousands of people started finding consistent differences in the types and amounts of bacteria men and women carry.
Scientific surveys, including the American Gut Project and the Human Microbiome Project, found that men tended to have more of certain bacterial types (like Prevotella and Ruminococcus), while women had more of others (like Bifidobacterium).2,3 These patterns held up even when researchers accounted for differences in diet and lifestyle.
Scientists also looked at how many different types of bacteria live in the gut based on sex. More diversity is generally better, and the picture here is nuanced: men showed higher diversity in some age groups, while women tended to maintain their gut diversity better as they get older, possibly because of the protective effects of estrogen on the gut lining.4 Even without factoring aging into the equation, hormones matter.
What you eat also plays a key role. On average, men tend to eat more red meat and less fiber-rich grains, fruits, and veggies than women. Fiber is basically food for your gut bacteria. Without enough of it, the beneficial bacteria that protect your health start to dwindle.5 This can leave men more vulnerable to three serious digestive conditions: acid reflux, ulcers, and colon cancer.
Acid reflux.
Most people have experienced heartburn—that burning feeling in the chest when stomach acid creeps back up your throat. When it happens on a regular basis, it’s called GERD (gastroesophageal reflux disease), a condition about one in five adults in Western countries deals with.6
Here’s where men have a real disadvantage: while women complain about heartburn more often, men are two to three times more likely to develop a serious complication called Barrett’s esophagus. This change in the lining of the esophagus can, over time, develop into cancer.7 Making matters worse, men tend to store more visceral fat around their abdominal organs. This fat physically squeezes the valve at the bottom of your esophagus—the one that’s supposed to keep stomach acid from coming back up—and weakens it.8
Studies also show that men with chronic acid reflux have a more unbalanced mix of bacteria in their esophagus, which further weakens the protective mucus lining and makes the problem worse over time.9
Stomach ulcers.
Ulcers are open sores that form in the lining of the stomach or the upper part of the small intestine. They’re about 50 percent more common in men than women.10
Two things cause most ulcers. The first is a bacterium called Helicobacter pylori that buries itself in the stomach lining. Research suggests that men infected with H. pylori have less variety in their gut bacteria overall, which means their bodies are less able to fight back against the damage this bug causes.11 The second cause is the use of common pain relievers like ibuprofen and aspirin among older men to relieve chronic discomfort like back pain or joint stiffness. Yet frequent use or taking high doses directly damage the stomach’s protective lining.12
Luckily, H. pylori is easy to detect with a breath test, stool test, or blood test. It’s quick, cheap, and could make a big difference. If you have it, a short course of antibiotics clears it up in more than 85 percent of cases and significantly cuts your risk of ulcers and stomach cancer down the road.
Colon cancer.
Colon cancer is the second-biggest cancer killer in the United States, and men get it at roughly 20 percent higher rates than women.13 Gut bacteria aren’t just bystanders here. Researchers have found that certain species are actually present inside colon tumors and fuel inflammation, which may help cancer develop and cancer grow.14 And here’s the kicker: men’s higher belly fat, lower fiber intake, and greater alcohol use create a gut environment where cancer-promoting bacteria thrive and protective ones disappear.
What you eat can make this worse. When gut bacteria process red meat, they produce chemicals called secondary bile acids, which are toxic to the cells lining your colon. This essentially causes damage that can eventually become cancer.15 At the same time, a low-fiber diet starves the bacteria that produce a protective substance called butyrate, which normally keeps colon cells healthy and prevents tumors from forming.16
The good news? Colon cancer is one of the most preventable cancers medicine knows of. A colonoscopy, starting at age 45 (earlier if it runs in your family), finds pre-cancerous growths before they become cancer. One clean colonoscopy every 10 years is one of the most powerful health decisions a man can make.
Tune Up Your Microbiome with Probiotics
Probiotic supplements seem to be everywhere, from health food stores to online retailers. Can they be a good thing for your gut? Absolutely, but here’s a reality check: they aren’t a magic bullet. Probiotics don’t move in and permanently change your microbiome. In most cases, they act like a short-term helping hand. As they pass through your gut, they compete with harmful bacteria for space and food, fortify your immune system, and help keep your gut lining strong and intact.17 But, because these benefits are transitory, it’s essential to take them every day.
One important thing to know: not all probiotics are the same. Different bacterial strains do completely different things. This is why matching the right probiotic to the right problem is important. For instance, a probiotic that contains Lactobacillus rhamnosus GG and Bifidobacterium longum can help clear H. pylori when taken alongside antibiotics.18 There’s also some evidence that a synbiotic (a supplement that combines prebiotics and probiotics) may help lower the risk of colon cancer.19 And some research suggests that probiotics like Lactobacillus gasseri and L. plantarum might even help to reduce belly fat.20
Just know this: not all probiotic supplements are the same. Look for a probiotic that:
- Lists the full name of what’s inside—genus, species, and strain code
- Uses DNA sequencing to ensure you’re getting the probiotic strains listed on the label
- Ensures the live bacteria is valid at the expiry date, not just when it was made
- Is shelf stable, no refrigeration needed
Remember, probiotics—even when combined with a prebiotic—can’t replace a healthy lifestyle. They won’t replace a colonoscopy. They won’t cure an H. pylori infection on their own. They won’t undo years of poor eating in a month. They are simply one very important tool in your gut health toolbox. The foundation of a healthy gut is still what you eat every single day—and no capsule can replace that.
