Gut Bacteria & Digestion
Explain how gut bacteria ferment some dietary fibre that human enzymes cannot digest, and how changes in the gut microbial community can affect digestion
What a learner can do afterwards
- Explains that many gut bacteria are beneficial, not harmful
- Describes how gut bacteria ferment some dietary fibre that human digestive enzymes cannot digest
- Explains what might happen if the gut microbiome is disrupted
1 · Read
The community of microbes in your gut is often called the gut microbiome. It includes bacteria and other microbes. Many gut bacteria help digestion, though some can cause illness. You have learned that human enzymes break down starch and protein. They cannot digest dietary fibre from plants. Bacteria in the large intestine can ferment some fibre, breaking it into smaller substances.
An apple contains sugars and fibre. Human enzymes cannot digest its fibre. Bacteria in the large intestine ferment some of it into short-chain fatty acids. Your body can absorb these small molecules, and gut-lining cells can use them for energy. Unfermented fibre leaves in faeces.
Antibiotics treat bacterial infections by killing bacteria or stopping their growth. Some also affect helpful gut bacteria. Changes in this community can affect fibre fermentation and digestion. Some people get bloating or diarrhoea, but effects and recovery times vary. Take prescribed antibiotics as directed. Ask a healthcare professional about concerns.
In a made-up lab example, equal-sized samples contain 50 bacterial cells before a treatment and 30 after it. Find the decrease by subtracting: 50 - 30 = 20 fewer cells. These are practice numbers, not a healthy gut's proportions. Cell counts do not tell you how many different bacterial types are present.
Two children's gut samples may contain different bacterial types. Recent antibiotic use could be one reason, but diet and other differences could also matter. The samples alone cannot establish the cause. Fewer bacterial types does not automatically mean worse digestion. Both children may digest food normally despite having different gut communities.
Gut bacteria ferment some fibre into useful molecules. Human enzymes digest other food molecules. Changes in gut bacteria can affect digestion, but effects vary.
Lesson, questions and flashcards written for this dataset.
Readings and flashcards written for this dataset. Linked video: TED-Ed, "How the food you eat affects your gut - Shilpa Ravella".
More to read
What happens to dietary fibre?
Some food molecules are broken down by human digestive enzymes. Dietary fibre is different: these enzymes cannot digest it. Fibre can therefore reach the large intestine, where bacteria can ferment some of it.
One group of products is called short-chain fatty acids. These small molecules can be absorbed by the body. Cells in the lining of the large intestine can use them for energy. Bacterial fermentation is therefore one way the body gains useful substances from material its own enzymes cannot digest.
There is still material left after fermentation. Some fibre remains unfermented and leaves in faeces. Finding fibre there does not mean digestion has stopped. Human enzymes and gut bacteria act on particular substances, and neither process breaks down everything you eat.
Reading changes in a gut community
A gut sample contains many bacterial cells, but a cell count and a count of bacterial types answer different questions. A sample could contain many cells belonging to only a few types. Counting cells alone does not reveal the variety of bacteria present.
Antibiotics can change a gut community because some affect helpful bacteria as well as bacteria causing an infection. Changes can affect digestion, and some people develop bloating or diarrhoea. The effects and recovery times vary. Take prescribed antibiotics as directed and ask a healthcare professional about concerns.
Suppose two children's samples contain different bacterial types and one child recently took antibiotics. The medicine is one possible explanation. Diet and other differences may also matter. Those two samples alone cannot establish the cause, and fewer detected types does not automatically mean poorer digestion.
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