Numerous websites have issued warnings about a condition called “leaky gut,” claiming that it can cause depression, anxiety, autoimmune disorders such as chronic fatigue, eczema, Hashimoto’s thyroiditis, joint pain, multiple sclerosis, rheumatoid arthritis and other disorders.

But is it real? And, if so, is it dangerous? And can you prevent it?

The condition is real, but physicians and scientists call it “intestinal hyperpermeability”—and so far, the research does not show that it’s the cause of all those conditions. Instead, the opposite appears to be true. Various health conditions can cause the intestine to become more porous and release more harmful substances that it should.

“It’s a myth that all these diseases start with a leaky gut,” explains Michael Camilleri, a gastroenterologist and professor at the Mayo Clinic College of Medicine and Science in Rochester, Minnesota. “What we do know is that certain diseases cause intestinal hyperpermeability,” he says. Examples are celiac disease, irritable bowel syndrome, Crohn’s disease, obesity, intestinal damage from using NSAIDS (non-steroidal anti-inflammatory medications), among others.

One of these diseases, irritable bowel syndrome (IBS), is the most commonly diagnosed digestive disorder, striking between 6 percent and 15 percent of American adults. Along with abdominal pain and bloating this disorder causes chronically abnormal bowel movements. A Mayo Clinic review found that up to 62 percent of people with diarrhea-prone IBS and up to 25 percent with the mainly constipation-type had intestinal hyperpermeability.

“But it remains unknown whether hyperpermeability is a cause of IBS,” Andrea Shin, a gastroenterologist and an associate clinical professor at the University of California Los Angeles Geffen School of Medicine, wrote in an email.

A little leakiness is good, a lot is not

To understand leaky gut, it helps to understand your GI tract’s life-or-death function: Bring nutrients into the body and keep out the bad stuff.

To do this, “the intestinal tract needs to be at least a little porous and permeable. It must allow the absorption of water and nutrients from digested food such as sodium, and small molecules such as glucose,” Camilleri says. After nutrients are absorbed into intestinal cells they migrate into the bloodstream and nourish the rest of the body.

To perform this absorption trick, specialized cells lining the intestine have semi-permeable walls. And even though they stand shoulder to shoulder, locked together with so called “tight junctions,” there’s still a little space for small molecules to slip through. That’s normal. Tight junction proteins are the glue that holds the cells together.

“But if the junctions loosen and the intestinal tract becomes too permeable—your health is at risk because substances that shouldn’t have access, such as not-completely-digested protein, or bacteria, get through. These can pass into your general circulation and, conceivably, damage organs,” Camilleri says.

No one’s quibbling over whether intestinal hyperpermeability is dangerous—it is. But where the medical establishment splits from some in the wellness industry is the cause, the diagnosis, and the treatment.

Testing for intestinal hyperpermeability

So how do you know if you have an abnormally leaky gut? Experts are dubious about test kits on the web.

“There isn’t a well-established non-invasive test that is scientifically and clinically valid. That’s why most intestinal permeability research has been conducted in animal and cell culture studies—scientists can more carefully study the gut and its function that way,” says Hannah D. Holscher, a dietitian and associate professor of nutrition at the University of Illinois Urbana-Champaign.

Shin concurs: “My patients ask if they can be tested for “leaky gut”, and I tell them that although different tools and methods are used in research, there is still no clear gold standard.”

“I don’t know of any commercially-available gut test kits that will diagnose leaky gut,” Mayo Clinic’s Camilleri says. However, he and his colleagues may have developed a diagnostic test that may soon be available. (He declares he has no financial interest in the new test.) It involves drinking liquid spiked with specific types of sugars, then collecting urine throughout the day to see how much is excreted. The more of these sugars that wind up in the urine, the more permeable the gut. Not exactly an easy test, but it’s proven to be accurate.

The diet/gut permeability connection

There is scant data revealing specific lifestyle factors that contribute to a dangerously leaky gut. But emerging research does indicate that diet can affect gut permeability in many ways. Here are a few:

Dietary fiber (fiber). Fiber-rich foods including fruits, vegetables, legumes, and whole grains help prevent constipation and maintain the mucus layer in the intestines, a defensive barrier that helps keep bacteria and other harmful substances from infiltrating intestinal cells and degrading the tight junctions between them.

“We have trillions of microorganisms in our GI tract; many of them use fiber from our diet for fuel. Without enough fiber some of these bacteria feed off the mucus layer, thinning it, so it’s no longer as protective. That could lead to increased gut permeability,” explains Holscher.

Diets high in fiber also expand populations of gut bacteria that produce short-chain fatty acids—which serve double-duty as healthy fuel for intestinal cells, and decrease inflammation, which is key for preserving healthy intestinal cells and their tight junctions.

Dietary fat. Nuts, seeds, seafood, and olive oil—staples of a Mediterranean diet—are rich in unsaturated “good” fat, that help decrease inflammation, while lowering blood cholesterol and possibly the risk of chronic diseases.