A new theory suggests that irritable bowel syndrome (IBS), the most common gastrointestinal disorder, could be caused by gravity.
Brennan Spiegel, MD, MSHS, director of health services research at Cedars-Sinai and author of hypothesisexplains that IBS – and many other conditions – could result from the body’s inability to deal with gravity.
“As long as there has been life on Earth, from the first organisms to Homo sapiens, gravity has relentlessly shaped everything on the planet,” said Spiegel, who is also a professor of medicine. “Our bodies are affected by gravity from the moment we are born until the day we die. It is such a fundamental force that we rarely notice its constant influence on our health.”
The hypothesis, published in the American Journal of Gastroenterologydescribes how the intestines, spine, heart, nerves, and brain evolved to deal with gravity.
“Our bodily systems are constantly pulled down,” Spiegel noted. “If these systems cannot handle the drag of gravity, it can lead to problems such as pain, cramps, dizziness, sweating, rapid heartbeat and back problems – all symptoms seen with IBS. It can even contribute to the bacterial overgrowth in the gut, a problem also linked to IBS.”
The underlying mechanism of IBS has baffled researchers since it was first described more than a century ago. While the disorder affects up to 10% of the world’s population, experts still don’t know exactly how or why it develops.
There are, however, several contrasting theories that explain its clinical characteristics. The first is that IBS is a gut-brain interaction disorder; evidence shows that neuromodulators and behavioral therapies are effective. Another theory holds that IBS is caused by abnormalities in the gut microbiome, which can be managed with antibiotics or low fermentation diets.
Other theories suggest that motility abnormalities, intestinal hypersensitivity, abnormal serotonin levels, or a dysregulated autonomic nervous system cause IBS.
“There is such a variety of explanations that I wondered if they could all be true simultaneously,” Spiegel said. “Thinking about every theory, from those involving motility to bacteria to the neuropsychology of IBS, I realized they could all point to gravity as a unifying factor. It seemed pretty strange at first, no doubt, but as I developed the idea and had it run by colleagues, it started to make sense.”
Gravity can compress the spine and decrease flexibility. It can also cause the organs to shift downward, moving from their correct position. Abdominal contents are heavy, like a sack of potatoes that we are destined to carry throughout our lives, Spiegel explained.
“The body has evolved to lift this load with an array of supporting structures. If these systems fail, IBS symptoms can arise along with musculoskeletal issues,” Spiegel said.
Some people have a body more capable of carrying the load than others. For example, some have “stretch” suspension systems that drop the intestines. Others have spinal problems that cause the diaphragm to sag or the belly to protrude, resulting in a compressed abdomen.
These factors can trigger motility problems or bacterial overgrowth in the gut. It may also help explain why physical therapy and exercise are effective for IBS, as these interventions strengthen support systems.
The gravity hypothesis, however, also goes beyond the intestines.
“Our nervous system also evolved in a world of gravity, and that might explain why many people experience abdominal ‘butterflies’ when they’re anxious,” Spiegel said. “It is curious that these ‘visceral sensations’ also occur when falling to Earth, such as when falling on a roller coaster or in a turbulent plane. The nerves in the intestine are like an ancient detector of G-force that alerts us when we are experiencing—or about to experience—a dangerous fall.This is only speculation, but people with IBS may be prone to overestimating G-force threats that never occur .”
Some people are more resistant to G-forces than others. For example, one person may raise their hands and smile while falling on a roller coaster while another clenches their teeth and moans. The first person is amused while the second feels threatened, revealing a specter of what Spiegel calls “G-force vigilance.”
Another contributor that may play a role is serotonin, a neurotransmitter that may have evolved in part to manage gravity in body systems. Serotonin is necessary for mood elevation, both metaphorically and literally, Spiegel noted. Without it, people also couldn’t stand upright, maintain balance, circulate blood, or pump intestinal contents against gravity.
“Dysregulated serotonin can be a form of gravity failure,” Spiegel said. “When serotonin biology is abnormal, people can develop IBS, anxiety, depression, fibromyalgia, and chronic fatigue. These can be forms of gravity intolerance.”
Further research is needed to test this approach and possible treatments.
“This hypothesis is very provocative, but the best thing is that it’s testable,” said Shelly Lu, MD, Women’s Guild Chair in Gastroenterology and director of the Digestive and Liver Diseases Division at Cedars-Sinai. “If true, this is a major paradigm shift in how we think about IBS and possibly treatment as well.”
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