Doctors have long told people to eat more fiber. It helps digestion, and it may also feed beneficial bacteria in the gut. But a new study says fiber alone isn’t enough. The type of bacteria in your gut matters. Furthermore, the specific strain of bacteria in your gut is also important.
The research was published in July in the journal Microbiology Spectrum. It was led by Angela Poole, a nutrition scientist at Cornell University. Her team looked closely at a common gut microbe called Bifidobacterium adolescentis. This bacterium helps break down resistant starch, a type of fiber the body can’t digest on its own.
Resistant starch is found in foods like beans, whole grains, and some vegetables. Past studies on its health benefits have been confusing. Some people seemed to benefit. Others didn’t. Poole’s team thinks they now know why. Not everyone has the right bacteria to process it. And having the right species isn’t enough. People need the right strain within that species.
Think of it like a lock and key. The bacteria are the key. Resistant starch is the lock. Only certain keys fit. A related strain of the same species might not work at all.
To test the hypothesis, researchers gathered stool samples from more than 50 people. They studied the bacteria living in each person’s gut. Then they gave the participants crackers to eat. Some crackers contained one type of resistant starch. Others contained a second type. A third batch had regular starch, which the body can break down without help from bacteria.
The team didn’t just look at which bacteria were present. That’s what older studies usually did. Instead, they used a newer method called shotgun metagenomics. This technique goes deeper. It can identify bacteria down to the strain level. It can also detect specific genes inside the bacteria.
Genes matter because they control what a bacterium can do. Some genes let a microbe produce enzymes. Those enzymes break down starch. Without the right genes, a bacterium can’t do the job, even if it belongs to a “helpful” species.
The researchers also used a new computer tool called Cayman. It helped them spot more genes linked to starch digestion. This tool proved especially useful for finding genes tied to resistant starch breakdown.
One surprising result came from the data. The team found new types of bacteria. The researchers discovered previously unstudied types of bacteria. before. These bacteria showed increased activity when resistant starch was present. This suggests that these bacteria may play a role in digesting resistant starch. Researchers plan to study these bacteria more closely in future work.
This discovery is relevant for something called precision nutrition. That’s the idea of designing diets based on a person’s unique biology. Poole gave an example. Imagine a doctor treating a diabetic patient. The doctor might test the patient’s gut bacteria. If Bifidobacterium adolescentis is present, that’s not enough information on its own. The doctor would need to know which strain the patient has. One strain might help control blood sugar. Another might do nothing at all.
Poole says better tools are needed going forward. Scientists must look past species names. They need to study genes and strains in detail. Only then can they know if someone’s gut bacteria can actually use a given type of fiber.
The study had two other lead researchers. Nicola Segata and Francesco Asnicar both work at the University of Trento in Italy. Funding came from Cornell University and the European Union. This research adds a new layer to how scientists think about fiber and digestion. It’s not just about eating enough. It’s about whether your body has the right microscopic tools to use it.
