(P25-010-25) Assessing the Impact of Walnut Consumption on Gut Health: Insights From Fecal Calprotectin and Short-Chain Fatty Acid Analysis

Objectives: To assess the impact of walnut consumption on the gut microenvironment by measuring changes in fecal calprotectin and short-chain fatty acids (SCFAs).

Methods: This study was a parallel-group, open label, randomized, controlled trial, in which 51 overweight and obese older adults (55-77 years old) were randomly allocated to a walnut or control group and followed for 12 weeks. Participants in the intervention arm were instructed to consume 1-3 oz of walnuts per day (~15% of energy intake) while those in the control group were advised to abstain from walnuts and limit consumption of other nuts to < 1serving/week. Dietary compliance was assessed through 24-hr dietary recalls and clinician interviews. Stool samples were collected at baseline and 12 weeks for analysis of fecal calprotectin (by enzyme-linked immunoassay) and SCFAs (by liquid chromatography—mass spectrometry). Multiple linear regression was used to test for changes over time between groups, after adjusting for baseline values.

Results: Fecal calprotectin increased in both groups over time, but the difference between groups was not significant. The amount of total SCFAs (in µmol/g) was significantly elevated on the walnut group compared to the control group (+124, p=0.033). All three of the primary SCFAs – butyrate, acetate, and propionate – were increased on the walnut group compared to the control group (+22, +30, and +10 respectively), however, the increase was statistically significant for butyrate only (p=0.048). None of the secondary SCFAs (isobutyric acid, 2-methylbutyric acid, isovaleric acid, valeric acid, 3-methylvaleric acid, caproic acid, isocaproic acid, heptanoic acid, octanoic acid, or nonanoic acid) were significantly altered by walnut consumption.

Conclusions: Walnut consumption over 3 months resulted in an increased level of total fecal SCFAs and specifically in higher amounts of butyric acid. This aligns with previous research indicating that walnuts enrich SCFA-producing microbial species in the gastrointestinal tract and suggests that walnuts may positively influence gut health. Further research is needed to verify this relationship.

Funding Sources: The California Walnut Commission