Nathan López Bezerra
New research shows that gut bacteria can change how they interact with the immune system based on the types of carbohydrates a person eats. The findings suggest that the same beneficial bacteria can either support or harm immune function depending on what they are fed.
Scientists focused on a bacterium called Bacteroides thetaiotaomicron, or B. theta, which makes up a large part of the gut microbiome in many people. This bacterium is known to play a role in immune function. The researchers studied B. theta by analyzing diet and gut samples from real people, testing mice that were given sugar water, and growing the bacteria with 190 different carbohydrates in a laboratory setting.
The study found that B. theta can change its genetic activity based on what a person eats. This means the bacteria can reprogram themselves to respond differently to the immune system. The type of carbohydrate consumed determines whether the bacteria produce compounds that reduce inflammation or create molecules linked to immune problems.
Natural fruit sugars were found to promote anti-inflammatory responses. Certain processed carbohydrates triggered pro-inflammatory reactions. The researchers also looked at people who regularly drank soft drinks with white sugar. Those people had B. theta bacteria that functioned differently compared to those who did not drink sugary beverages.
The sugar did not just affect digestion. It compromised the gut’s protective barrier and weakened immune defenses. People who drank sugary drinks had lower levels of immune cells that help fight infections and poorer gut tissue repair. These changes happened within a few weeks and continued to evolve over time.
The findings help explain why the same diet can work well for one person but not for another. Each person’s gut bacteria respond differently to the same foods based on their unique microbiome composition. The changes are not permanent. As a person adjusts their diet, their gut bacteria quickly adapt their behavior.
The researchers suggest that people can choose carbohydrates that encourage beneficial bacterial responses without making drastic dietary changes. Rotating carbohydrate sources each week, such as switching between sweet potatoes, quinoa, oats, and different fruits, can expose bacteria to varied nutrients. Paying attention to energy levels, mood, and digestion after eating different carbohydrates can help people identify what works best for them.
Combining fiber-rich carbohydrates with meals, such as adding berries to yogurt or vegetables to grains, provides diverse fuel for gut bacteria. Limiting sugary drinks and replacing them with water infused with fruit or herbal teas can avoid negative effects on the gut microbiome.
The carbohydrates a person eats act like daily instructions for their gut bacteria. Sugary drinks and processed carbohydrates tend to push gut bacteria toward inflammatory responses. Whole food carbohydrates encourage anti-inflammatory, health-supporting behaviors. The bacteria are adaptable, and feeding them a variety of fiber-rich, whole food carbohydrates can support immune function, mood, and overall health.
