A 2023 review explored whether the length of time poop stays in the body before being passed affects the gut bacteria.
They looked at earlier studies involving thousands of people, including both healthy individuals and those with conditions like irritable bowel syndrome, constipation, and liver disease. The studies included information on diet, stool type, gut bacteria, and the chemicals those bacteria produce.
Measuring how fast food moves through the gut, called gut transit time, included swallowing small sensor capsules that track movement through the digestive system. Another common method is the Bristol Stool Scale, which classifies stool from hard lumps to watery. Some studies also tracked how long it takes for things like corn or food coloring to pass through the body.
All these methods help estimate how long food stays in the colon. The longer it stays, the more time bacteria have to break it down and produce substances that can affect health.
The researchers found that people with fast digestion had very different gut bacteria compared to those with slow digestion. People with faster digestion often have bacteria that grow quickly and prefer high-carb, low-fat diets. Those with slower digestion sometimes had bacteria that prefer protein. In both very fast and very slow cases, the variety of gut bacteria was lower than in people with average digestion speed.
Overall, the study suggested that gut transit time is an important but often ignored factor in understanding gut health. It may also explain why the same diet doesn't work the same way for everyone, as two people can eat the same food but get different results depending on how fast their digestion works.
Gut transit time may also affect how well probiotics, supplements, or medicines work, meaning that understanding a person's unique digestion speed could help doctors give more personalized diet and treatment advice.
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