New research shows that gut bacteria can change how they interact with the immune system based on the type of carbohydrates a person eats. The study suggests that dietary choices can reprogram these microbes, moving beyond the simple idea of good or bad bacteria.
Scientists focused on a bacterium called Bacteroides thetaiotaomicron, or B. theta, which makes up a large part of the gut microbiome in many people and plays a role in immune function. The research team studied this bacterium in three ways. They analyzed diet and gut samples from real people. They also tested mice given sugar water. Finally, they grew the bacteria in a lab with 190 different carbohydrates.
The findings show that B. theta can change its genetic activity based on what a person eats. This change alters how the bacterium interacts with the immune system. The researchers described this as the gut bacteria having the ability to reprogram themselves depending on food choices.
Different Carbs, Different Bacterial Behavior
The team tested 190 carbohydrates and found that each one caused B. theta to act differently. Some carbohydrates triggered the bacteria to produce compounds that reduce inflammation and support gut health. Other carbohydrates caused the same bacteria to create inflammatory molecules linked to immune problems.
The type of carbohydrate a person eats determines whether their gut bacteria help or harm the immune system. Natural fruit sugars promoted anti-inflammatory responses. Certain processed carbohydrates triggered pro-inflammatory reactions.
The researchers also looked at the effect of sugar. They found that people who regularly drank soft drinks with white sugar had B. theta bacteria that functioned differently than those who did not drink these beverages. The sugar did not just affect digestion. It weakened the gut’s protective barrier and lowered immune defenses. There were also fewer immune cells that help fight infections. The changes happened within a few weeks and continued over time.
Why Standard Diets May Not Work for Everyone
This research helps explain why the same diet can work well for one person but not for another. Gut bacteria respond differently to the same foods based on each person’s unique microbiome composition. The changes in bacterial behavior are not permanent. As a person adjusts their diet, their gut bacteria quickly adapt. This means people can choose carbohydrates that encourage beneficial bacterial responses without making drastic changes to their diet.
Some practical steps include rotating carbohydrate sources each week. Switching between sweet potatoes, quinoa, oats, and different fruits exposes bacteria to varied nutrients. Paying attention to how the body feels after eating different carbohydrates can also help. Noting energy levels, mood, and digestion can guide food choices. Combining fiber-rich carbohydrates with meals, such as adding berries to yogurt or vegetables to grains, provides diverse fuel for bacteria. Limiting sugary drinks and replacing them with water infused with fruit or herbal teas can also support gut health.
The study indicates that every meal offers a chance to guide gut bacteria toward better immune function. Sugary drinks and processed carbohydrates tend to push gut bacteria toward inflammatory responses. Whole food carbohydrates encourage anti-inflammatory, health-supporting behaviors. The findings suggest that people do not need to eliminate entire food groups. Instead, focusing on a variety of fiber-rich, whole food carbohydrates can support the immune system, mood, and overall health. The research was published in Nature Communications.
