Why do some people feel healthier after eating more fibre while others notice little difference?
A new study suggests the answer may not be the amount of fibre people eat, but the tiny bacteria living inside their gut.
The research, published in Microbiology Spectrum, shows that even different versions of the same type of bacteria can respond to food in very different ways.
Dietary fibre is found in beans, lentils, whole grains, vegetables, fruit, nuts and seeds.
Unlike many other foods, some types of fibre cannot be fully broken down by the body’s own digestive system. Instead, gut bacteria do much of the work, producing helpful substances that support digestion, gut health and blood sugar control.
One important type of fibre is called resistant starch. It passes through the stomach and small intestine mostly unchanged before reaching the large intestine. There, bacteria break it down and produce compounds that may benefit the body.
Scientists have known for years that resistant starch helps some people more than others. Researchers have wondered why the results have been so different. The new study points to the bacteria living in the gut as an important part of the answer.
The research team, led by Angela Poole from Cornell University, studied gut bacteria from more than 50 volunteers. Participants ate crackers containing two different forms of resistant starch and, at another time, a normal starch that could be digested without help from gut bacteria.
Instead of using older laboratory methods that only identify broad groups of bacteria, the scientists used a more detailed technique called shotgun metagenomics. This method allowed them to identify bacteria down to individual strains and study the genes that help them digest food.
The researchers focused on a common gut bacterium called Bifidobacterium adolescentis. Although many people carry this bacterium, they found that different strains behaved very differently. Some strains were very good at breaking down resistant starch, while others were much less effective.
The team also used a new computer tool called Cayman to identify genes involved in fibre digestion. This helped them discover several bacteria that had not previously been recognised as playing a role in breaking down resistant starch.
These findings suggest that simply knowing which bacterial species someone has may not be enough. Doctors may also need to know the exact strain and the genes it carries before predicting whether a person will benefit from a particular high-fibre diet.
This idea is known as precision nutrition. Instead of giving everyone the same dietary advice, doctors may one day recommend foods based on each person’s gut bacteria. Such an approach could be especially useful for people with diabetes or other long-term health conditions where controlling blood sugar is important.
The researchers say more studies are needed before this becomes routine medical care. Larger studies involving more people and different populations will help confirm the findings and show how they can be used in everyday healthcare.
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