What is already known on this topic
Gut microbes have been associated with several conditions — from allergies to autism. However, whether alterations in microbiota composition are the cause or consequence of disease is unclear, partly because it’s difficult to determine what a “healthy” microbiota is.

What this research adds
Researchers characterized the gut microbiota of 530 healthy people from Spain. The two most dominant bacterial phyla were Firmicutes and Bacteroidota, followed by Proteobacteria, Verrucomicrobiota, and Actinobacteriota. This microbiota composition has been already reported in healthy individuals. As expected, several microbial markers appeared to be associated with variables such as sex, age, and diet. For example, the researchers found a decrease of Faecalibacterium with age, a link of Flavonifractor with poorer dietary habits, and the association of Eubacterium eligens with the Mediterranean diet.

Conclusions
By describing the Spanish “healthy” microbiota, the study could provide a baseline for future work investigating the effects of gut microbiota composition on health and disease. The findings also suggest that the Mediterranean diet could have indirect effects on health through a not-yet fully understood association between specific foods, microbial markers, and beneficial health outcomes.

Gut microbes have been associated with several conditions — from allergies to autism. However, whether alterations in microbiota composition are the cause or consequence of disease is unclear, partly because it’s difficult to determine what a “healthy” microbiota is. Now, a team of researchers from Spain have characterized the “normal” microbiota of Spaniards and its link to the Mediterranean diet.

The findings, published in Scientific Reports, could provide a baseline for future work investigating the effects of gut microbiota composition on health and disease. “The present work constitutes the first complete analysis of the gut microbiome of a Mediterranean country,” the authors say. “Our findings clearly confirm the association between some of the foods that characterize the Mediterranean diet (vegetables and nuts, basically) with the abundance of bacterial taxa which, in turn, are associated with health benefits.”

Previous studies have shown that several factors, including climate, lifestyle and diet, can influence the microbial composition of the gut. For this reason, in order to determine what a normal microbiota is, scientists should assess the natural variability in healthy individuals living in the same region or country.

A team of researchers led by Adriel Latorre-Pérez at Darwin Bioprospecting Excellence S.L. and Marta Hernández at the Instituto Central Lechera Asturiana para la Nutrición Personalizada set out to analyze the gut microbiota of 530 healthy people from Spain. The team also collected information on diet habits from 528 of the study participants.

The Spanish microbiota

In the samples analyzed, the two most dominant bacterial phyla were Firmicutes and Bacteroidota, followed by Proteobacteria, Verrucomicrobiota, and Actinobacteriota. This microbiota composition has been already reported in healthy individuals.

People from the Balearic Islands had the lowest microbial diversity, whereas individuals from two regions in Northern Spain showed the highest diversity, the researchers found. Gut microbiotas of men and women were similar, although men had higher abundances of Proteobacteria and Faecalibacterium.

Several microbial markers were associated with age, the team found. In particular, the abundance of Bifidobacterium decreased with age, whereas that of Cyanobacteria increased.

Mediterranean diet markers

A number of microbial markers were also associated with diet. For example, Flavonifractor levels were increased in people who consumed sugar-sweetened drinks, but reduced in individuals who consumed nuts, fruits, and vegetables. Flavonifractor bacteria have been linked to different conditions, including bipolar disorder and colorectal cancer.

The team also found that the abundance of Ruminococcus torques increased in people who consumed meat. On the other hand, Eubacterium eligens was common in people who ate green beans, chard, spinach, salad and nuts, but not in those who consumed hamburgers and sausages.

Eubacterium eligens has been linked to a higher adherence to the Mediterranean diet and to a beneficial health signature. “Considering that the Spanish population mainly follows the [Mediterranean diet], Flavonifractor (or F. plautii), Ruminococcus torques group, and Eubacterium eligens group could be proposed as gut microbial markers of adherence to this diet,” the researchers say.