White-bread fans can rest a little easier—this much-maligned food may help to encourage the growth of beneficial gut bacteria, according to researchers from the University of Oviedo in Spain.

In addition to this surprising find, their study in the American Chemical Society’s Journal of Agricultural and Food Chemistry also revealed that when looking at effects of food on our “microbiome,” considering the whole diet, not just individual ingredients, was critical.

Sonia González and colleagues noted that the bacteria in the gut, or the microbiome, played an important role in our health. When certain populations of bacteria drop, people become more prone to disease. One of the most effective ways to maintain a good balance of the microbes living in the gut is through the diet.

To find out what dietary ingredients promote helpful bacteria, several studies have looked at the effects of individual fibers and probiotics. But the University of Oviedo researchers said few studies had investigated the role of polyphenols, which are common in much of what we consume — spices, teas, fruits and vegetables — or how polyphenols and fibers together help balance our gut microbes. González’s team wanted to fill that gap.

The researchers asked 38 healthy adults questions about their diets and figured out which bacteria were present in the participants’ stool samples.

The researchers said the most novel finding was that white bread boosted Lactobacillus, a group of beneficial bacteria.

Their analysis also found that pectin, a compound in citrus fruits, lowers the levels of some helpful bacteria. This is contrary to previous research on pectin alone. The researchers suggest that pectin might interact with other substances in oranges, leading to this unexpected effect.

The authors acknowledged funding from the Spanish Ministry of Science and Innovation.

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