Radical new breathing technique ‘Butt Breathing’ confirmed safe in human trial

Breathing through your backside may sound like science fiction, but a Japanese clinical trial recently suggested that one day it might help human beings with lungs that can't get enough oxygen.

The study tested whether a specialized liquid called perfluorodecalin could be safely stored in the rectum for an hour. No one was injured, and that alone is telling news. It is the first time that this "enteral ventilation" approach, based on a fish that breathes from its intestines, has been attempted on humans.

The story starts with a kind of eel fish called a loach. When kept in filth, low-oxygen water, it does something strange—it swallows air and absorbs oxygen in the intestines. The strange trick caught the attention of Japanese researcher Takanori Takebe, MD, PhD, a biomedical scientist with appointments in Tokyo and at Cincinnati Children's Hospital. At the height of the COVID-19 pandemic, when ventilators had been used up in hospitals worldwide, Takebe was left wondering whether humans ever learned from the loach's example.

The notion might seem laughable, but it is science-driven. The active ingredient is odorless, colorless liquid perfluorodecalin—a perfluorocarbon that had previously been under investigation for "liquid breathing." The liquid can hold several times more oxygen than water and has already been used safely in surgery and eye treatments.

The idea is simple but revolutionary: if the fluid is filled with oxygen and the gut can absorb gases, why not use the gut as an auxiliary respiratory organ in the event of lung failure?

The new trial translated that question from the lab to the clinic. The phase 1 study took place at a Japanese hospital, where it recruited young men who volunteered to inject small amounts of non-oxygenated perfluorodecalin into their rectum for an hour. Scientists were not testing whether it would save lives—but whether it was safe.

The process was serious, not jesting. Fluid was added gradually through a soft catheter, and volunteers were monitored closely for signs of pain, shifts in vital signs, or chemical indication of the fluid in their systems. The purpose was simple: determine the amount of fluid man could hold safely and whether their bodies reacted negatively to it.

The results were surprisingly peaceful. Every one except a few tolerated the process well. Some reported bloating or cramping with higher volumes, but pain disappeared once the fluid was released. No one had negative, severe side effects, and blood tests showed no liver, kidney, or blood chemistry damage. Most significantly, the fluid didn't intrude into the circulatory system—it stayed right where it was supposed to.

Even without added oxygen, perfluorodecalin contains more dissolved oxygen than venous blood. In theory, a small amount could diffuse through the intestinal wall and into the bloodstream.

The researchers did note weak signs that this was happening, but not enough to have a clinical effect yet. That's not surprising—this was a safety study, not a rescue experiment. But it sets up the second trial, which will use fully oxygenated liquid to see if it can measurably boost oxygen in people with low blood oxygen levels.

To Takebe, who himself won an Ig Nobel Prize once—a tongue-in-cheek prize for science that "first makes people laugh, then think"—this is no joke. "Enteric ventilation might be a life-saver as a back-up mode of oxygen delivery," he said. "Our initial results suggest that it could save patients with severe respiratory failure when conventional ventilation fails."

If future tests confirm that oxygenated perfluorodecalin can boost blood oxygen, the procedure might revolutionize the treatment of respiratory distress for doctors. In an emergency, it might save precious minutes as doctors intubate a patient or prepare a ventilator. With fragile newborn lungs, it might be a more compassionate way to deliver oxygen without causing additional harm. And in global tragedies—when hospitals drain machines—there to serve as a low-tech salvation.

Researchers at EVA Therapeutics, founded by Takebe, are already planning the next round of trials in Japan. They will maximize how much liquid can be used, how long it should stay there, and how much oxygen might make its way into the blood. The hope is one day this strange-sounding solution might make a difference in quiet ways.

Behind the humor is a vigorous warning: medical breakthroughs tend to begin with concepts that sound preposterous. After being dismissed as a curiosity, the breathing of the loach in its intestines now serves as the foundation for a potential new technique for maintaining human life. With ventilators in short supply and respiratory arrest still being fatal, even the most absurd concepts deserve a second review.

If the trials prove out that oxygenated perfluorodecalin is safe to deliver oxygen through the intestine, hospitals may have a new tool in the respiratory crisis arsenal.

The method could lower the risk of ventilator-induced damage, support delicate newborn lungs, and give life-saving aid when other machinery is unavailable.

It also challenges scientists to re-conceive human physiology and teaches us that sometimes survival is more about imagination than medicine.

Research findings are available online in the journal ScienceDirect Med.

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