Minimal Association Between Immunoglobulin A Coating and Gut Microbiota Alterations Induced by High-Fat Diets with Distinct Fatty Acid Compositions

High-fat diets (HFDs) containing dietary fats with different fatty acid (FA) compositions alter gut microbiota composition in a fat-source-dependent manner. Immunoglobulin A (IgA) and unabsorbed lipids in the distal gut are potential regulators of the gut microbiota. However, their roles in mediating gut microbiota alterations induced by dietary fats with different FA compositions remain unclear. This study aims to examine the associations of these two factors with fat-source-dependent gut microbiota alterations. BALB/c mice were fed a normal diet, a high-lard diet, a high-olive oil diet, or a high-soybean oil diet for 27 weeks. Fecal samples were collected to assess microbiota composition, the IgA coating index (ICI)—which quantifies the extent of IgA coating on gut microbiota—and fecal fatty acid concentrations. At the phylum level, the concentration of fecal total long-chain fatty acids (LCFAs) was positively correlated with the relative abundance (RA) of Bacillota and negatively correlated with that of Bacteroidota. In addition, a trend toward a positive association between the RA and the ICI was observed for Bacillota but not for Bacteroidota. At the genus level, the RAs of 12 taxa were positively correlated with fecal LCFA concentrations, whereas those of 6 taxa were negatively correlated. Although the RAs of most taxa appeared to be influenced by unabsorbed lipids and additional factors, only four Bacillota genera exhibited a positive correlation between the RA and the ICI. Our observations suggest that IgA coating of the gut microbiota may have a minimal association with fat-source-specific alterations in gut microbiota composition during HFD intake.