Effects of Dietary Glucose, Fructose, and Monosaccharide-to-Lard Energy Ratios on Cecal Microbiota Composition and Ecological Organization in Rats.

Background

Although dietary fat and carbohydrates are major determinants of gut microbiota composition, their interactive effects across changing dietary monosaccharide-to-lard energy ratios remain incompletely understood. This study descriptively examined treatment-level cecal microbiome profiles across dietary gradients in which lard (L) was progressively replaced with glucose (G) or fructose (F).

Methods

A carbohydrate-free, lard-rich control diet was formulated, and lard was progressively replaced with glucose or fructose while maintaining a constant protein-to-energy ratio. Cecal contents from eight rats per dietary group were pooled in equal amounts, yielding one composite microbiome sample per treatment. Pooled samples were characterized by shotgun metagenomic sequencing. Sequencing/classified read counts (CRs) and relative abundance (RA) were treated as complementary sequencing-derived representations rather than measures of absolute bacterial abundance. Microbiome outcomes were interpreted descriptively at the treatment level.

Results

Across the pooled treatment profiles, CRs and RA showed non-linear patterns and did not consistently change in parallel, providing complementary descriptions of treatment-level taxonomic responses. CR patterns indicated a combined effect of L and monosaccharide content, with several mixed L-monosaccharide diets showing lower CRs than both the L6.03 reference and the lard-free endpoints. Differences between the G and F series were most apparent at low L and high monosaccharide levels, particularly under lard-free conditions, although their magnitude and direction varied among taxa. Hierarchical clustering and exploratory correlation networks provided complementary descriptions of treatment-level community organization.

Conclusions

The pooled treatment-level microbiome profiles revealed non-linear responses to changing dietary L-monosaccharide composition, with CRs and RA providing partly different information on taxonomic patterns. Differences between the G and F series were most apparent at low L and high monosaccharide levels, particularly under lard-free conditions.