There's an invisible and relentless force acting on your bowels right now, and it might be causing some people serious irritation.
No one really knows how or why irritable bowel syndrome (IBS) develops, but gastroenterologist Brennan Spiegel from Cedars-Sinai hospital in Los Angeles has outlined a weighty new hypothesis.
In a paper published in The American Journal of Gastroenterology, Spiegel argues IBS is triggered by the body's inability to manage gravity.
Our bowels, Spiegel explains, are like a big sack of potatoes that we have to carry around our whole lives.
If our body's usual management of gravity fails for whatever reason, our diaphragm can slip down and compress our intestines, possibly causing motility issues and bacterial overgrowth.
"Our nervous system also evolved in a world of gravity, and that might explain why many people feel abdominal 'butterflies' when anxious," says Spiegel.
"It's curious that these 'gut feelings' also occur when falling toward Earth, like when dropping on a roller coaster or in a turbulent airplane. The nerves in the gut are like an ancient G-force detector that warns us when we're experiencing – or about to experience – a dangerous fall. It's just a hypothesis, but people with IBS might be prone to over-predicting G-force threats that never occur."
The nice part about Spiegel's hypothesis is that it's easily testable and doesn't exclude other theories of IBS.
Currently, there is no definitive test for IBS, and its symptoms are extremely variable from patient to patient. As a result, the syndrome is usually made as a diagnosis of exclusion.
Once other disorders that can cause gut symptoms – such as pain, bloating, cramping, constipation, or diarrhea – have been ruled out, patients are usually told they have IBS.
Today, about 10 percent of people worldwide are thought to suffer from the syndrome, and Spiegel is one of many scientists working to figure out why.
Gravity, he argues, might be the grounding force that pulls all these different symptoms together.
Under Spiegel's framework, a disordered response to gravity might also trigger a gut-to-brain interaction disorder. By squashing the intestines, it might even impact the gut microbiome, causing hypersensitivity, inflammation, or discomfort.
"There's such a variety of explanations that I wondered if they could all be simultaneously true," says Spiegel.
"As I thought about each theory, from those involving motility, to bacteria, to the neuropsychology of IBS, I realized they might all point back to gravity as a unifying factor. It seemed pretty strange at first, no doubt, but as I developed the idea and ran it by colleagues, it started to make sense."
If IBS is caused by the body struggling to grapple with gravity, then it could explain why physical therapy and exercise can prove so beneficial in relieving its symptoms.
It could also explain why serotonin tends to be elevated in IBS patients.
Serotonin is a neurotransmitter that is primarily produced in the gut to regulate our bowel movements and also our mood, but too much of it can trigger diarrhea. It is also involved in the regulation of our blood pressure in response to gravity.
Without serotonin, Spiegel says, your body might not be able to stand up, maintain balance, or continue circulating blood.
"Dysregulated serotonin may be a form of gravity failure," argues Spiegel.
"When serotonin biology is abnormal, people can develop IBS, anxiety, depression, fibromyalgia, and chronic fatigue. These may be forms of gravity intolerance."
Chronic fatigue syndrome/ myalgic encephalomyelitis (CFS/ME) is another chronic and debilitating sickness without a cause or cure, and it often crosses over with IBS. Many CFS/ME patients also struggle with standing up, which can cause a sudden drop in blood pressure, fatigue, dizziness, and a racing heart.
Other symptoms that cross over with IBS include lower back pain, headaches, dizziness and postural tachycardia syndrome (POTS), which is when blood pressure plummets after a person rises.
All of these conditions could be explained by the body's inability to properly manage the force of gravity.
Without direct research, Spiegel says the gravity hypothesis is just a "thought experiment". But he hopes it encourages new ways of researching and treating IBS in the future.
"Our relationship to gravity is not unlike the relationship of fish to water," writes Spiegel.
"We live our entire life in it, are shaped by it, yet hardly notice its ever present influence on the nature of our existence."
Perhaps it's about time we considered it.
The study was published in The American Journal of Gastroenterology.