Very low-carbohydrate, high-fat ketogenic diets (KDs) induce a pronounced shift in metabolic fuel utilization that elevates circulating ketone bodies; however, the consequences of these compounds for host-microbiome interactions remain unknown. Here, we show that KDs alter the human and mouse gut microbiota in a manner distinct from high-fat diets (HFDs). Metagenomic and metabolomic analyses of stool samples from an 8-week inpatient study revealed marked shifts in gut microbial community structure and function during the KD. Gradient diet experiments in mice confirmed the unique impact of KDs relative to HFDs with a reproducible depletion of bifidobacteria. In vitro and in vivo experiments showed that ketone bodies selectively inhibited bifidobacterial growth. Finally, mono-colonizations and human microbiome transplantations into germ-free mice revealed that the KD-associated gut microbiota reduces the levels of intestinal pro-inflammatory Th17 cells.Together, these results highlight the importance of trans-kingdom chemical dialogs for mediating the host response to dietary interventions.

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) caused by demyelination, immune cell infiltration, and axonal damage. Herein, we sought to investigate the influence of physical exercise on mice experimental autoimmune encephalomyelitis (EAE), a reported MS model. Data show that both strength and endurance training protocols consistently prevented clinical signs of EAE and decreased oxidative stress, an effect which was likely due to improving genomic antioxidant defense-nuclear factor erythroid 2-related factor (Nrf2)/antioxidant response elements (ARE) pathway-in the CNS. In addition, physical exercise inhibited the production of pro-inflammatory cytokines interferon (IFN)-γ, interleukin (IL)-17, and IL-1β in the spinal cord of mice with EAE. Of note, spleen cells obtained from strength training group incubated with MOGshowed a significant upregulation of CD25 and IL-10 levels, with a decrease of IL-6, MCP-1, and tumor necrosis factor (TNF)-α production, mainly, during acute and chronic phase of EAE. Moreover, these immunomodulatory effects of exercise were associated with reduced expression of adhesion molecules, especially of platelet and endothelial cell adhesion molecule 1 (PECAM-1). Finally, physical exercise also restored the expression of tight junctions in spinal cord. Together, these results demonstrate that mild/moderate physical exercise, when performed regularly in mice, consistently attenuates the progression and pathological hallmarks of EAE, thereby representing an important non-pharmacological intervention for the improvement of immune-mediated diseases such as MS. Graphical Abstract Schematic diagram illustrating the beneficial effects of physical exercise during experimental model of MS. Physical exercise, especially strength (ST) and endurance (ET) training protocols, inhibits the development and progression of disease, measured by the mean maximal clinical score (1.5 and 1.0, respectively), with inhibition of 30 % and 50 %, respectively, based on the AUC, compared with EAEuntreated group. In addition, ST and ET decreased oxidative stress, possibly, through genomic antioxidant defense, Nrf2-Keap1 signaling pathway, in the CNS. Physical exercise inhibited the production of inflammatory cytokines, such as IFN-γ, IL-17 and IL-1β in the spinal cord after EAE induction, as well as spleen cells obtained from ST group showed a significant upregulation of regulatory T cell markers, such as CD25 andIL-10 levels, and blocked IL-6, MCP-1 and TNF-α production, mainly, during acute and chronic phase of EAE. Finally, these immunomodulatory effects of exercise were associated with inhibition of adhesion molecules and reestablishment of tight junctions expression in spinal cord tissue, thereby limiting BBB permeability and transmigration of autoreactive T cells to the CNS. NO, nitric oxide; GPx, glutathione peroxidase, GSH, glutathione; Nrf2, nuclear factor (erythroid-derived 2)-like 2; CNS, central nervous system; BBB, blood-brain barrier; IFN-g, interferon-gamma; IL-17, interleukin 17; IL-1b, interleukin-1beta.