The gut microbiota plays an important role in maintaining the body's homeostasis, and its disruption has been linked to the pathogenesis of coronary atherosclerosis and cognitive decline. This review attempted to assess whether the composition of the gut microbiota differs significantly according to the severity of coronary atherosclerosis and whether the presence of specific cytokines and inflammatory markers in the microbiota of patients with atherosclerosis may correlate with cognitive impairment. In addition, it considered whether increased dietary fiber intake may contribute to lower levels of inflammatory markers compared to a low-fiber diet. This review included publications from 2015 to 2024, searched in the PubMed and Scopus databases. Only studies meeting the quality criteria were included. The pooled data indicate that intestinal dysbiosis can lead to increased intestinal barrier permeability and lipopolysaccharide (LPS) translocation, which promotes chronic inflammation. This process plays an important role in both atherosclerosis and neurodegeneration. In addition, some studies indicate a beneficial effect of dietary fiber in reducing inflammatory markers. The conclusions of this review highlight the need for further, well-designed studies to identify the causal relationship between the microbiota, its metabolites, atherosclerosis, and cognitive deficits, which may provide the basis for new therapeutic strategies.