Fecal microbiomes from healthy adult consumers of fruits and vegetables exhibit fiber- and donor-specific fermentation: "5 a day" is not enough.

To determine the fermentation capacity of gut microbiomes with diverse plant carbohydrate active enzyme (CAZyme) repertoires, we collected fecal samples from 18 healthy adults who reported consuming at least 5 different fruits and vegetables daily and conducted shotgun metagenome analysis. Five fecal samples with the most diverse CAZymes were then fermented in vitro with 7 different fibers selected for their unique monosaccharide profiles-banana, kale,13-bean soup, flax, coconut flour, MS Prebiotic (resistant starch) and Sunfiber (guar gum)-for 72 hours. Samples were collected at 4 timepoints for 16S sequencing, and pH, SCFAs, and monosaccharide measurements. The largest changes in pH, microbial diversity, monosaccharides, and short chain fatty acids (SCFAs) occurred in the first 24 hours of fermentation. SCFA production was highest with flax and lowest with coconut flour. Fermentation patterns ranged from little change to primary degradation (liberated monosaccharides) to robust production of SCFAs. Abundance of Bifidobacteriaceae, Butyricicoccaceae, and Ruminococcaceae correlated with the highest fermentation, Clostridiaceae, Enterococcaceae, and Eggerthellaceae with the lowest. Samples from three of the participants were more responsive than the other two. The donor-specific and fiber-specific responses seen in our study indicate that dietary guidance to consume 5 servings of fruits and vegetables per day may not be enough to ensure that our gut microbiota is capable of unlocking all of fiber's benefits.