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

Authors: BLECKSMITH, SARAH - University Of California, Davis; KALANETRA, KAREN - University Of California, Davis; WENG, CHENG-YU - University Of California, Davis; SUAREZ, CHRISTOPHER - University Of California, Davis; SITEPU, IRNAYULI - University Of California, Davis; TANG, YIRUI - University Of California, Davis; CHEANG, SHAWN - University Of California, Davis; JIANG, SOPHIA - University Of California, Davis; CERNIOGLO, KARINA - University Of California, Davis; DAMIAN-MEDINA, KARLA - University Of California, Davis; SMILIOWITZ, JENNIFER - University Of California, Davis; LEBRILLA, CARLITO - University Of California, Davis; MILLS, DAVID - University Of California, Davis; Lemay, Danielle

Submitted to: Food & Function
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2025
Publication Date: 9/8/2025
Citation: Blecksmith, S.E., Kalanetra, K.M., Weng, C., Suarez, C., Sitepu, I., Tang, Y., Cheang, S.E., Jiang, S., Cernioglo, K., Damian-Medina, K., Smiliowitz, J.T., Lebrilla, C.B., Mills, D.A., Lemay, D.G. 2025. Fecal microbiomes from healthy adult consumers of fruits and vegetables exhibit fiber- and donor-specific fermentation: "5 a day" is not enough. Food & Function. https://doi.org/10.1039/D5FO00947B.
DOI: https://doi.org/10.1039/D5FO00947B

Interpretive Summary: All dietary fiber is not alike as fiber can comprise many different structures with different physiological effects. To study the degradation of complex fibers, we recruited 18 healthy adults who regularly eat fruits and vegetables and studied the microbiomes of their fecal samples. We selected the five fecal samples with highest genetic capacity for degrading fiber and conducted fermentation experiments with fibers selected for their unique structures —banana, kale,13-bean soup, flax, coconut flour, MS Prebiotic (resistant starch) and Sunfiber (guar gum). Fermentation outcomes varied by fiber type with larger than expected differences by donor. Current dietary guidance to consume 5 servings of fruits and vegetables per day and 14 grams of fiber per 1000 calories may not be enough to ensure that our gut microbiomes are capable of unlocking all of fiber’s benefits.

Technical Abstract: 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. The largest changes in pH, microbial diversity, monosaccharides, and SCFAs occurred in the first 24 hours of fermentation. SCFA production was highest with flax, 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 microbiomes are capable of unlocking all of fiber’s benefits.