Gut bacteria trained by fiber can reverse fatty liver disease, study shows

A new UC Irvine study may have finally uncovered how dietary fiber protects the body from sugar’s damage, and how protecting yourself starts in the gut.

Researchers at the UCI School of Medicine found that inulin, a naturally occurring fiber found in vegetables like onions, garlic and artichokes, can reshape the bacteria living in your gut to stop fructose before it hits your liver.

“We found that consuming a type of dietary fiber called inulin… changes the bacteria in the gut to promote the consumption of harmful dietary fructose,” said lead researcher Cholsoon Jang, PhD, of UCI’s Nutrient Metabolism & Disease Lab. 

The findings, published in Nature Metabolism, reveal a new level of protection offered by fiber, not just in digestion, but in how the body handles sugar at the molecular level.

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Jang and his team discovered that when people eat fructose (a common sugar in fruit and sweetened foods) gut bacteria in the small intestine can metabolize it before it reaches the liver. But without enough fiber, too much fructose “spills over,” overwhelming the liver and triggering fat buildup.

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By feeding gut bacteria with inulin, researchers found that the microbes essentially burn through fructose early, preventing that cascade of damage. 

Even more striking, once these bacteria were “primed” by inulin, they were able to reverse signs of fatty liver disease, reducing fat accumulation and boosting the liver’s natural antioxidants.

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Jang says the research proves not all calories are created equal.

He says their work gives “insight into how fiber protects our health from harmful nutrients like fructose.”

The study focused on non-obese participants: people who might otherwise slip under the radar yet still face hidden risks from high-sugar diets. 

Jang noted that metabolic damage isn’t limited to those who are overweight. Even people who appear healthy can experience liver stress and insulin resistance if their gut microbes aren’t equipped to handle excess fructose.

“By identifying specific gut bacteria and metabolic pathways involved, our findings can guide personalized nutrition strategies,” Jang said.

He added that future research will explore whether other common fibers beyond inulin can trigger similar protective effects.

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The implications stretch far beyond the lab. If certain fibers can train gut microbes to neutralize sugar before it harms the liver, it could open the door to new treatments for fatty liver disease, diabetes, obesity and even cancer.

For now, researchers explain that the findings indicate that fiber not only aids digestion but can be a defender of metabolic health.

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As Jang put it: “For example, by checking how well someone’s gut bacteria clears fructose before the body absorbs it, we can choose the right prebiotic or probiotic supplement for that person to improve results and reduce side effects.”