A team of researchers in Japan and the United States is investigating a surprisingly promising medical idea: whether humans can absorb oxygen through the gut when the lungs are unable to function normally.
The experimental concept — often described as “butt breathing” — is being led by Dr. Takanori Takebe, a stem cell biologist at Cincinnati Children’s Hospital Medical Center and the University of Osaka. The project began after Takebe watched his father struggle on a ventilator during a severe pneumonia infection, prompting him to search for alternative ways to support patients when traditional breathing support becomes risky or insufficient.
Inspired by animals that breathe through their skin and guts
Takebe’s interest grew after learning how certain animals, including loach fish, can absorb oxygen through unconventional body parts such as skin, genitals or intestines. Humans, he realised, also have a highly vascular intestinal tract, which absorbs medication from enemas directly into the bloodstream — raising the question: Could oxygen be absorbed the same way?
A special oxygen-rich enema shows promising results
The research team developed an enemalike treatment using perfluorodecalin, a medical liquid capable of carrying large amounts of oxygen. Once infused into the rectum, the oxygen diffuses into the bloodstream, while carbon dioxide dissolves back into the liquid.
Early experiments in mice and pigs delivered remarkable results.
In pigs, each 400 ml dose increased blood oxygen levels for around 19–30 minutes. Blood samples even changed from dark red to bright red as oxygen levels rose — Takebe’s “aha moment”.
The findings were published in Med in 2021 and 2023, and in 2024 the project earned an Ig Nobel Prize, a humorous award celebrating science that “makes people laugh, then think”.
Human safety trials: How much liquid can the body handle?
Takebe’s team has now completed the first human safety trial.
Twenty-seven healthy men in Japan were given non-oxygenated perfluorodecalin in varying volumes, from 25 ml up to 1.5 litres — the maximum amount approved for GI contrast imaging.
The results, published December 12 in Med, show:
- Doses up to 1 litre were largely tolerable
- The largest dose (1.5 L) caused too much abdominal pain for most volunteers
- Mild bloating and discomfort were the most common side effects
The trial was funded by EVA Therapeutics, a startup co-founded by Takebe to commercialise the technology.
Experts divided on the future of gut-based oxygen delivery
Some physicians believe the idea has limited potential.
Dr. John Laffey, a respiratory specialist at the University of Galway, argues that even damaged lungs will always exchange gas much more efficiently than the gut. He also notes the challenge of sustaining oxygen levels, since each litre of liquid only holds about 500 ml of oxygen, while a ventilated patient may need that much every two minutes.
But others see niche, lifesaving uses.
Dr. Kevin Gibbs, a pulmonary critical care specialist at Wake Forest University, says the technique could buy doctors valuable time during high-risk procedures — such as inserting a breathing tube in a patient with dangerously low oxygen levels.
“If this gives even a short burst of extra oxygen during a critical moment, that could be huge,” he said.
Years away, but full of potential
Takebe envisions the method as a short-term supplement — useful in emergencies, during ambulance transfers, or alongside other forms of respiratory support.
Full clinical trials using oxygen-loaded liquid will determine whether the technique can actually oxygenate human blood. Any real-world use, Takebe admits, is still many years away.
As for his father — the person who inspired the research — he’s fully supportive.
“Dad is pleased,” Takebe says with a smile. “He’s always offering to volunteer.”