Relationships Between High Dietary Inflammatory Index Scores and Intestinal and Blood–Brain Barrier Integrity in the Context of Neurodegenerative Diseases

The impact of diet on human health is constantly being researched. Nutrition is one of the most powerful tools for influencing gene expression, and dietary habits can promote the expression of genetic predisposition to obesity, diabetes, cardiovascular disease, cancer, and neurodegenerative diseases (NDs). The dietary inflammatory index (DII) is a numerical score that assesses the pro-or anti-inflammatory potential of a given diet. According to high DII scores, a Western diet or a standard American diet (SAD) has proinflammatory properties. By disrupting the gut microbiome, SAD creates an unfavorable environment in the intestine that is associated with a low-grade systemic inflammatory response and oxidative changes that may promote the development of NDs. An increased intestinal permeability and loss of blood‒brain barrier (BBB) integrity play key roles in the pathomechanisms of diet-dependent NDs, leading to proinflammatory signaling via the gut‒brain axis. The aim of this narrative review is to present in detail the current state of knowledge on the function of the gut–brain axis depending on the pro-/anti-inflammatory potential of the diet, measured by the DII, in the context of the contributions of intestinal and BBB permeability disorders to the development of NDs.