Physical Activity and Inflammation Phenotype Conversion

Abstract

Inflammation is a protective response to infection or injury; however, persistent microtraumas at the tissue level may result in chronic low-grade inflammation that plays both direct and indirect roles in the development of many diseases and aging. The purpose of this review is to describe the underlying physiology of low-grade inflammation and highlight potential inflammation lowering effects of physical activity (PA). Unique contributions of this review are to introduce the concept of inflammation phenotype flexibility in contrast to the low-grade inflammation state and describe how PA influences inflammation phenotype by altering muscle, gut, adipose, and postprandial metabolism. Pro-inflammatory M1 macrophages and cytokines—such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6—contribute to low-grade inflammation. Among the mechanisms that commonly contribute to low-grade inflammation are dysfunctional adipose tissue, a leaky gut, gut microbiota that promotes inflammation, and large postprandial glycemic and lipidemic responses. Physical activity may lower inflammation by decreasing M1 macrophages in visceral adipose tissue, decreasing adipose tissue volume, production of anti-inflammatory myokines, promotion of butyrate-producing members of the gut microbiota, improved gut barrier function, and lowering of postprandial glycemic and lipidemic responses. While exercise has many anti-inflammatory mechanisms, phenotype conversion is complex, multifaceted, and difficult to achieve. Our understanding of how PA influences inflammation must include acute exercise-induced anti-inflammatory effects, contribution to the inflammation state from multiple sources in the body, and phenotypic shifts underpinning low-grade inflammation.