Impact of mixed nut consumption on faecal lipid content and gut microbiota composition in healthy adults

Nuts are a source of dietary fibre and are considered a nutritious snack despite their high fat content. The effects of nut consumption on the microbiota and the role of nut-derived lipids in altering the large intestinal microbial community remain poorly understood. This study examined changes in faecal characteristics and microbiota composition in 15 healthy volunteers consuming unrestricted diets during a cross-over dietary intervention consisting of three weeks of daily mixed-nut consumption (30 g almonds, macadamias and pistachios) and three weeks of nut abstinence. Microscopic examination of faecal samples revealed lipid-containing nut particles following nut consumption, which were not observed during the nut abstinence. Mixed nut consumption was associated with a significant increase in total faecal lipid content compared with nut abstinence (P < 0.05), suggesting incomplete digestion and absorption of nut-derived lipids. In contrast, faecal pH, dry matter, ash content, short-chain fatty acids and ammonium concentrations were not significantly altered by the intervention. 16S rRNA gene sequence analysis demonstrated substantial inter-individual variation in gut microbial community composition, with only modest differences associated with nut consumption. Predicted functional profiling suggested variation in pathways related to lipid metabolism between intervention periods. Overall, the findings indicate that a portion of consumed nut cells likely reaches the large intestine intact. Upon degradation of the nut cell wall, encapsulated lipids may become available to the colonic microbiota, potentially contributing to microbial metabolism and community responses observed.