Timing of unsaturated fat intake improves insulin sensitivity via the gut microbiota-bile acid axis: a randomized controlled trial

The timing of dietary total fat intake influences glucose homeostasis, however, the impact of unsaturated fat (USFA) intake has yet to be explored. This 12-week, double-blind, randomized, controlled, 2 × 2 factorial-designed feeding trial investigated the effects of timing (lunch or dinner) and types of dietary USFA (high monounsaturated fat or polyunsaturated fat diet) intake on glucose metabolism in seventy prediabetes participants (mean age, 57 years). Sixty participants with completed fecal samples were included in the final analysis (n = 15 for each group). Postprandial serum glucose was first primary outcome, postprandial insulin levels and insulin sensitivity indices were co-primary outcomes Secondary outcomes were continuous glucose levels, serum fatty acid profile, gut microbiome (metagenomic sequencing) and fecal metabolites. Results showed no significant differences in postprandial glucose between groups. However, USFA intake at lunch (vs. dinner) improved insulin sensitivity and reduced postprandial insulin and serum free saturated fatty acid (Ptiming 0.05, Pinteraction > 0.05), which was associated with alterations in gut microbiome and bile acid metabolism, regardless of USFA type. In summary, these results suggest that advancing timing of USFA intake improves insulin sensitivity through the gut microbiome and bile acid metabolism. Trial registration: ChiCTR2100045645.