The crosstalk between the gut microbiota and lipids
Les relations bidirectionnelles entre le microbiote intestinal et les lipides
Philippe Gérard OCL 18 November 2020
The human intestine harbours a complex and diverse bacterial community called the gut microbiota. This microbiota, stable during the lifetime, is specific of each individual despite the existence of a phylogenetic core shared by the majority of adults. The influence of the gut microbiota on host’s physiology has been largely studied using germfree animals and studies using these animal models have revealed that the effects of lipids on host physiology are microbiota-dependent.
Studies in mice have also shown that a high-fat diet rapidly and reproducibly alters the gut microbiome. In humans, dietary fat interventions did not lead to strong and consistent modifications of the microbiota composition. Nevertheless, an association between total fat intake and the reduction of the microbiota richness has been repeatedly found. Interestingly, different types of fat exert different or even opposite effects on the microbiota. Concurrently, the gut microbiota is able to convert the lipids entering the colon, including fatty acids or cholesterol, leading to the production of metabolites with potential health effects.
Résumé
L’intestin humain héberge une communauté bactérienne complexe et diverse appelée microbiote intestinal. Ce microbiote, stable au cours de la vie, est spécifique à chaque individu malgré l’existence d’un noyau phylogénétique partagé par la majorité des adultes. L’influence du microbiote intestinal sur la physiologie de l’hôte a été largement étudiée en utilisant des animaux sans germes. Ces études ont en particulier révélé que les effets des lipides sur la physiologie de l’hôte sont dépendants du microbiote. Chez l’animal il a également été montré qu’un régime alimentaire riche en lipides modifie rapidement et de manière reproductible le microbiote intestinal. Chez l’homme, des études nutritionnelles impliquant des lipides n’ont pas entraîné de modifications fortes et cohérentes de la composition du microbiote. Néanmoins, une association entre la consommation de lipides et la réduction de la richesse du microbiote a été constatée à plusieurs reprises. Il est intéressant de noter que différents types de lipides exercent des effets distincts, voire opposés, sur le microbiote. Par ailleurs, le microbiote intestinal est capable de convertir les lipides présents dans le côlon, en particulier les acides gras ou le cholestérol, aboutissant à la production de métabolites ayant des effets potentiels sur la santé.
Conclusion
The interactions between the lipids and the gut microbiota are bidirectional. First, it is clear that dietary fats shape the gut microbiota composition with effects depending on the quantity and quality of the lipids. Also, the gut microbiota is able to metabolize the part of the lipids that enter the colon and to produce lipid metabolites that may impact host health. A poor explored issue is how this relationship influences host lipid metabolism. Comparison of GF and conventional mice has shown that the gut microbiota affects lipid composition in the serum, adipose tissue, and liver, with its greatest effect on triglyceride and phosphatidylcholine species (Velagapudi et al., 2010). Moreover, the gut microbiota induces hepatic production of MUFA and elongation of PUFA and regulates FA synthesis in the liver. The gut microbiota may also impact blood lipid levels and it was found in humans that triglycerides were higher and HDL-cholesterol were lower in individual with low microbiota diversity (Le Chatelier et al., 2013). Moreover, it was recently revealed that the gut microbiota regulates host cholesterol homeostasis (Le Roy et al., 2019). Finally, a cross-validation analysis performed on a cohort study revealed that the gut microbiome contributes to a substantial proportion of the variation in blood lipids, with 6% of variance of serum triglycerides and 4% in HDL attributed to the microbiota composition (Fu et al., 2015). This highlights that the gut microbiota must be taken into account when one aims to assess the effects of lipids on health and disease.
