Abstract
Omega-3 polyunsaturated fatty acids (omega-3 PUFAs), which are essential fatty acids that humans should obtain from diet, have potential benefits for human health. In addition to altering the structure and function of cell membranes, omega-3 PUFAs (docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), alpha-linolenic acid (ALA), and docosapentaenoic acid (DPA)) exert different effects on intestinal immune tolerance and gut microbiota maintenance. Firstly, we review the effect of omega-3 PUFAs on gut microbiota. And the effects of omega-3 PUFAs on intestinal immunity and inflammation were described. Furthermore, the important roles of omega-3 PUFAs in maintaining the balance between gut immunity and the gut microbiota were discussed. Additional factors, such as obesity and diseases (NAFLD, gastrointestinal malignancies or cancer, bacterial and viral infections), which are associated with variability in omega-3 PUFA metabolism, can influence omega-3 PUFAs–microbiome–immune system interactions in the intestinal tract and also play roles in regulating gut immunity. This review identifies several pathways by which the microbiota modulates the gut immune system through omega-3 PUFAs. Omega-3 supplementation can be targeted to specific pathways to prevent and alleviate intestinal diseases, which may help researchers identify innovative diagnostic methods.
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Key Points
Gut microbes play vital roles in maintaining intestinal health. Nutrients exert profound effects on gut microbes and intestinal immunity. Nutrients and intestinal immunity are mediated by gut microbes, and there is a strong correlation between these factors. As essential fatty acids, dietary omega-3 PUFAs participated in regulating gut immunity and the maintenance of gut homeostasis, which are associated with the gut microbiota, fatty acid metabolism, and intestinal health. In this review, how omega-3 PUFAs interact with the gut microbiota, how omega-3 PUFAs modulate gut immunity, and the relationship between gut microbes and intestinal immunity are discussed. The factors that alter the interaction among omega-3 PUFAs, gut microbes, and intestinal immunity will be discussed. These discussions might provide new insights into the prevention or treatment of diseases related to disorders of omega-3 PUFA metabolism or intestinal microbes.
Omega-3 PUFAs affect the gut microbiome in three main ways: (1) modulating the type and abundance of gut microbes; (2) altering the levels of proinflammatory mediators, such as endotoxins (lipopolysaccharides) and IL17; and (3) regulating the levels of short-chain fatty acids or short-chain fatty acid salts. The effect of omega-3 PUFAs on the gut microbiota may be a main contributor to the health benefits of omega-3 PUFAs. Omega-3 PUFAs are mainly absorbed in the gut, where some microorganisms can directly utilize omega-3 PUFAs and produce numerous small molecules. Studies have highlighted the changes in the gut microbiota after omega-3 PUFAs supplementation.
Omega-3 PUFAs could directly affect the gut microbiota, and correspondingly, the gut microbiota could directly or indirectly modulate the absorption, bioavailability, and biotransformation of omega-3 PUFAs and further influence the imbalance of PUFA intake and its function. Gut microbes produce PUFA-derived metabolites, which may be novel active metabolites. PUFA-derived intermediate metabolites are produced by a wide range of bacteria, including lactic acid-producing bacteria. In addition, the in vitro stimulation and in vivo administration of PUFA-derived bacterial metabolites results in antiobesity and anti-inflammatory effects. Based on accumulating evidence, omega-3 PUFAs (DHA, EPA, and ALA) exert profound effects on the intestinal microbiota, the host-microbiome interaction, and interactions between the host immune system and gut microbiota. Accordingly, the gut microbiota modulates the absorption and metabolism of omega-3 PUFAs and directly or indirectly modulates subsequent physiological and immune responses in the host. In previous studies, researchers focused on the trends in the host digestion and absorption of omega-3 PUFAs, while the effects of gut microbes on omega-3 PUFAs have often been neglected. Therefore, further comprehensive studies about the effects of omega-3 PUFAs on gut microbes and gut immunity will be meaningful.
Factors such as obesity and diseases are associated with host gut microbes, gut immunity, and omega-3 PUFAs. Omega-3 PUFAs modulate gut immunity by acting on gut microbes. In addition, omega-3 PUFAs are a feasible approach to maintain gut health. However, the composition of the gut microbes is complex, and simply using one substance will not be an effective method to solve these problems; individualized treatments for patients should be developed.