Dietary lipid intake can influence the gut microbiota (GM) and their metabolites, such as short-chain fatty acids (SCFA) and bile acids, which are key mediators of health. The objective is to examine how dietary lipids’ quantity and quality influence the GM and metabolite profiles. A literature review of 33 studies in animals and humans was performed on the effects of saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs), polyunsaturated fatty acids (PUFAs), trans-fatty acids (TFAs), and sterols on GM composition and gut-derived metabolites. The results show that diets rich in MUFAs, n-3 PUFAs, and short-chain FAs have the potential to enhance beneficial bacteria and metabolites. In addition, trans-palmitoleic acid, conjugated linoleic acid, and phytosterols may also have potentially beneficial effects on GM, but more research is needed. Medium-chain FAs and n-6 PUFAs have variable effects on the GM. Conversely, intakes of high-fat diets, long-chain SFAs, industrial TFAs, and cholesterol disrupt GM balance. In conclusion, animal studies clearly demonstrate that dietary fats influence the GM and related metabolites. Yet, human studies are limited. Therefore, well-designed human studies that consider the whole diet and baseline health status are needed to better understand the effects of dietary lipids on GM.

Industrially originated trans-fatty acids (I-tFAs), such as elaidic acid (EA), and ruminant trans-fatty acids (R-tFAs), such as trans-palmitoleic acid (TPA), may have opposite effects on metabolic health. The objective was to compare the effects of consuming 2–3% I-tFA or R-tFA on the gut microbiome and fecal metabolite profile in mice after 7 and 28 days. Forty C57BL/6 mice were assigned to one of the four prepared formulations: lecithin nanovesicles, lecithin nanovesicles with EA or TPA, or water. Fecal samples and animals’ weights were collected on days 0, 7, and 28. Fecal samples were used to determine gut microbiome profiles by 16S rRNA sequencing and metabolite concentrations by GC/MS. At 28 days, TPA intake decreased the abundance of Staphylococcus sp55 but increased Staphylococcus sp119. EA intake also increased the abundance of Staphylococcus sp119 but decreased Ruminococcaceae UCG-014, Lachnospiraceae, and Clostridium sensu stricto 1 at 28 days. Fecal short-chain fatty acids were increased after TPA while decreased after EA after 7 and 28 days. This study shows that TPA and EA modify the abundance of specific microbial taxa and fecal metabolite profiles in distinct ways.

Two distinct types of trans fatty acids (TFA) are found in the diet. Industrial TFA such as elaidic acid (EA) have deleterious effects on metabolic risk factors, and oppositely ruminant TFA including trans-palmitoleic acid (TPA) may have beneficial effects. The objective is to evaluate the taste preference between EA, TPA, lecithin or water. In this study, 24 female C57BL/6 mice were microchipped and placed in two separate IntelliCages^®. Nano encapsulated TFA or lecithin were added to drinking water in different corners of the cage with normal diet. The study was carried out over 5 weeks, during which mice were exposed to water only (weeks 1 and 3), TFA or lecithin (week 2), and EA or TPA (weeks 4 and 5). Mice weights, corner visits, nose pokes (NP), and lick number were measured each week. The results demonstrated that mice consume more TFA, either EA or TPA, compared with lecithin. In addition, the mice licked more EA compared with TPA in one cage; conversely, in the other cage they licked more TPA compared with EA. However, when TFA positions were swapped, mice had equal licks for EA and TPA. In sum, mice preferred TFA, in equal matter compared with controls; therefore, the results demonstrate the potential for TFA-type substitution in diet.