Engineering SCFAs with dietary fibre combinations: insights from a kinetic-microbiome single-subject longitudinal study.

The human diet plays a pivotal role in health, yet many studies seeking to identify health-promoting foods rely on experimental designs that poorly reflect natural circumstances. The effects of dietary fibres on the microbiota are typically examined using pooled faecal material and isolated fibres, creating unrealistic environments. Additionally, little progress has been made in distinctly characterising the fermentation rates of dietary fibres. To evaluate the temporal dynamics of gut microbial composition and metabolite production, as well as to characterise the fermentation rates of dietary fibres at an individual level, we conducted an n-of-1 longitudinal study examining responses to eight distinct dietary fibres, fermented both individually and in combination. A blend of sugarcane fibre and cassava resistant starch produced significantly higher butyrate levels (p < 0.0001) than either fibre alone. Microbial profiling showed that inulin and pectin selectively enriched Bifidobacterium spp. Anaerobutyricum hallii was increased with psyllium husk, wheat dextrin, and banana resistant starch, but decreased with a mixture of sugarcane fibre and cassava resistant starch (p < 0.0001). Fermentation kinetics were distinctly categorised into "fast", "medium", "slow" and "poorly-fermentable". These findings indicate that combinations of dietary fibres can be used as a strategy to engineer synergistic health-promoting metabolite responses in an individual, while establishing a standardised framework for describing fermentation rates across studies.