Abstract
Growing evidence supports the hypothesis that dietary factors may play a role in systemic low-grade chronic inflammation. Summary evidence from randomized controlled trials has shown substantial effects on biomarkers of inflammation following the adoption of plant-based diets (including, but not limited to, the Mediterranean diet), while consistent findings have been reported for higher intakes of whole grains, fruits, and vegetables and positive trends observed for the consumption of legumes, pulses, nuts, and olive oil. Among animal food groups, dairy products have been shown to have the best benefits on biomarkers of inflammation, while red meat and egg have been shown to have neutral effects. The present review provides an overview of the mechanisms underlying the relation between dietary factors and immune system, with a focus on specific macronutrient and non-nutrient phytochemicals (polyphenols) and low-grade inflammation. Substantial differences within each macronutrient group may explain the conflicting results obtained regarding foods high in saturated fats and carbohydrates, underlying the role of specific subtypes of molecules (i.e., short-chain fatty acids or fiber vs. long chain fatty acids or free added sugars) when exploring the relation between diet and inflammation, as well as the importance of the food matrix and the commixture of foods in the context of whole dietary patterns. Dietary polyphenols and oligopeptides have been hypothesized to exert several functions, including the regulation of the inflammatory response and effects on the immune system. Overall, evidence suggests that dietary factors may affect the immune system regardless of obesity-related inflammation.
Highlights
Over the last 100 years, nutritional sciences have attempted to understand the role of nutrition as a major determinant of health [1]
As imbalance between caloric intake and energy expenditure occurs, excess energy is stored in adipocytes, which increase in number and volume: the resulting hyperplasia and hypertrophy of the adipose tissue lead to oxygen depletion and the establishment of a condition of cellular suffering that leads to the recruitment of M1 macrophages, a type of macrophage that express high levels of pro-inflammatory receptors (i.e., Toll-like receptors (TLRs), tumor necrosis factor receptors (TNFRs), and interleukin-1 receptor (IL-1R)) and high activation of the nuclear factor-kB (NF-kB) transcription factors for pro-inflammatory molecules [7]
Results from observational studies support the hypothesis that a higher adherence to dietary patterns in line with the Mediterranean diet principles and, in general, a diet that is rich in plant-based foods is associated with lower serum concentrations of C-reactive protein (CRP) levels and a lower risk of elevated inflammatory biomarkers, while “Westernized” dietary patterns characterized by an excess intake of empty calories, processed meats, sodium, fats, and free sugar have been associated with higher levels of inflammatory biomarkers [40,41]
Summary
Over the last 100 years, nutritional sciences have attempted to understand the role of nutrition as a major determinant of health [1]. Excess lipids that fail to be stored in the adipose tissue are deposited in other organs (such as liver, skeletal muscle, and blood vessels), leading to the expression of proinflammatory mediators, the differentiation of monocyte to macrophage, and the recruitment of M1 macrophages at a systemic level [10]. This chronic condition can establish a vicious circle characterized by increased central adiposity, intrahepatic fat accumulation, vascular inflammation, and impairment of endothelial function with cardiovascular sequelae of the central nervous system and various organs and tissues [11]. The aim of this review is to explore current knowledge on the relation between dietary factors mediating inflammation, including the clinical evidence for food groups and dietary patterns exerting anti-inflammatory effects and the potential mechanisms potentially explaining the observed effects
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