Conference Coverage

Western diet linked to lower microbiome diversity


 

REPORTING FROM GMFH 2019

MIAMI – Eating a Western diet correlated with significantly lower gut microbiome diversity in an observational study of 1,000 healthy men and women.

Fast carbohydrates food Assortment of unhealthy products happy_lark/iStock/Getty Images

The chief culprits were fried foods, sodas, fatty sweets, processed meats, ready-cooked meals, and desserts, reported Valentin Partula, a PhD student at the Université Paris 13 Nord and his associates. The more often individuals reported consuming these, the fewer bacterial species were identified in their stool (P less than .05 for each association), the investigators wrote in a poster presented at the annual Gut Microbiota for Health World Summit.

Studies have linked decreased microbiota diversity with health conditions ranging from inflammatory bowel disease and colorectal cancer to diabetes mellitus. Obesity also is characterized by a less diverse microbiome and is linked to many of the same diseases, but the diversity (richness) of the gut microbiome appears to have more to do with diet than body mass index. However, interventional studies linking diet to microbiome shifts often have been small, narrow in scope, and short in duration, the researchers noted at the meeting sponsored by the American Gastroenterological Association and the European Society for Neurogastroenterology and Motility.

To help fill these gaps, they administered a 19-item food-frequency questionnaire to 1,000 healthy men and women in France who were 20-69 years old. Each food question had six possible responses, ranging from “at least twice a day” to “never.” For 862 of these men and women, the researchers also analyzed stool samples using 16S rRNA sequencing – a standard test for microbiome diversity. These sequencing results were analyzed in terms of both alpha diversity (the number of species within a sample, and the relative abundance of each) and beta diversity (the degree of dissimilarity among different individuals).

The most significant correlate of low alpha diversity (that is, a less diverse gut microbiome) was frequent consumption of fried foods, followed by sodas or sugary drinks, fatty sweet products, processed meats, ready-cooked meals, and desserts (P less than .05 for each). Conversely, raw fruits and fish each correlated with having a richer microbiome (P less than .05). Consuming eggs and raw and cooked vegetables also correlated with greater diversity, but these associations did not reach statistical significance.

In terms of beta diversity (uniqueness of the microbiome signature), the strongest correlates were fresh fruit, fried products, ready-cooked meals, and cheese. The finding for fresh fruit might be an effect of weighting but needs further study, the researchers said. Taken together, however, the findings “extend and support mechanistic arguments linking Western diet to altered microbiota composition,” they said.

Next, they looked at how specific foods correlated with specific bacterial taxa. Consuming more dairy correlated with a greater abundance of Streptococcus salivarius, which disrupts S. pyogenes biofilms in the pharynx and thus might help prevent bacterial pharyngitis. Eating raw fruits was tied to increases in Eubacterium eligens, a nonpathogenic bacterium whose role in the gut remains unclear. Finally, frequent cheese consumption was linked to lower abundance of Akkermansia muciniphila, a bacterium that is thought to benefit metabolic pathways and immune signaling.

For the same 846 individuals, the researchers performed 1hydrogen nuclear magnetic resonance metabolomic tests on plasma Carr-Purcell-Meiboom-Gill (CPMG)–pulse sequence and nuclear Overhauser enhancement spectroscopy (NOESY). Increased creatinine was associated with the highest number of bacterial taxa and might reflect effects on kidney function or trimethylamine N-oxide, they wrote. Greater microbiome diversity correlated with higher plasma levels of amino acids, proteins, creatinine, choline, glucose, and citrate. Lower diversity was tied to the presence of lipid-based metabolites, including ketones and esters.

The next step is to confirm the findings in a separate population and establish which of these associations are probably causal, the researchers wrote. “Mechanistic studies elucidating the metabolic capability of the organisms [also] are needed.”

No external funding sources or conflicts of interest were reported.

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