“Previous work has shown that fiber is converted by gut bacteria into chemicals known as short-chain fatty acids, and these in turn can have a variety of health benefits such as reducing inflammation and maintaining the integrity of the gut barrier,” says senior study author Alexandre Almeida, PhD, a researcher at the University of Cambridge’s Department of Veterinary Medicine in England.
“We found that short-chain fatty acids showed the strongest protective signal [against the risk of infections], suggesting that fiber consumption could have a positive effect in this context.”
In addition, the study results suggest that eating more fiber to support beneficial bacteria may help crowd out harmful bacteria from the Enterobacteriaceae family, including Klebsiella pneumoniae (which can cause pneumonia and meningitis), shigella, and E. coli.
At low levels, these bacteria are part of a healthy human gut microbiome — but overgrowth increases the chances of a dangerous infection.
Why High-Fiber Diets May Protect Against Infection
A computational analysis of gut microbiome composition based on more than 12,000 stool samples from 45 countries highlighted how increased fiber intake feeds protective bacteria from the genus Faecalibacterium.
The large-scale analysis, published this month in the journal Nature Microbiology, concluded that microbiome composition may predict whether a person’s gut is likely to be colonized by Enterobacteriaceae. The scientists identified 135 gut bacteria species commonly present when Enterobacteriaceae is absent, including Faecalibacterium.
“By using new AI technology and analyzing a large sample of humans, this study lends support for the concept that we should adopt a diet that has fiber to rebalance and maintain our healthy microbiome,” says Dr. Ghannoum, who was not involved in the research.
Questioning the Value of Probiotic Supplements
Although Dr. Almeida and his collaborators did not specifically test the effects of probiotics, their results indicated that probiotics may not directly change the environment in the gut. Probiotics may compete for the same nutrients as bad gut bacteria, but that may not stop the disease-causing bacteria from getting established in the gut, according to the study authors.
“If we want to make a positive change to our gut microbiome, it may be more effective to facilitate the growth of a wide range of good bacteria — for instance through diet — than to introduce any one particular set of species [of bacteria] through probiotics,” says Almeida.
Julia Zumpano, RD, a registered dietitian with the Cleveland Clinic Center for Human Nutrition, says that probiotic foods that may improve gut bacteria include sauerkraut, kimchi, miso, kefir, yogurt, and kombucha.
Boosting Your Fiber Intake
Many food sources are high in fiber, according to Zumpano, who was not involved in the study:
- Fruits, such as berries, bananas, apples, pears, avocado, and kiwi
- Vegetables, such as dark leafy greens, artichokes, broccoli, Brussels sprouts, cabbage, cauliflower, and turnips
- Legumes, such as lentils, chickpeas, black beans, kidney beans, and pinto beans
- Whole grains, such as quinoa, wild rice, farro, buckwheat, and oats
She further urges eliminating or decreasing consumption of processed and convenience foods that are often low in fiber:
- Processed meats
- Baked goods
- Fried and fast food
- Sweets and desserts
- Soda
- Processed fat (margarine and shortening)
More Research Needed, Especially in Light of Rising Antibiotic Resistance
One limitation of the study noted by Almeida is that the study was observational, meaning it was performed on the gut microbiome of people at one point in time.
“This means that future work is needed to experimentally test whether certain things like fiber and other nutrients directly prevent the incidence of infections in a longer timespan,” he says.
He adds that an alarming global rise in antibiotic resistance to Klebsiella pneumoniae is leading scientists to look for new ways of keeping it, and other similar infectious bacteria, under control.
“With higher rates of antibiotic resistance there are fewer treatment options available to us. The best approach now is to prevent infections occurring in the first place, and we can do this by reducing the opportunities for these disease-causing bacteria to thrive in our gut,” says Almeida.