Feeding our immune system: impact on metabolism

Abstract

Endogenous intestinal microflora and environmental factors, such as diet, play a central role in immune homeostasis and reactivity. In addition, microflora and diet both influence body weight and insulin-resistance, notably through an action on adipose cells. Moreover, it is known since a long time that any disturbance in metabolism, like obesity, is associated with immune alteration, for example, inflammation. The purpose of this review is to provide an update on how nutrients-derived factors (mostly focusing on fatty acids and glucose) impact the innate and acquired immune systems, including the gut immune system and its associated bacterial flora. We will try to show the reader how the highly energy-demanding immune cells use glucose as a main source of fuel in a way similar to that of insulin-responsive adipose tissue and how Toll-like receptors (TLRs) of the innate immune system, which are found on immune cells, intestinal cells, and adipocytes, are presently viewed as essential actors in the complex balance ensuring bodily immune and metabolic health. Understanding more about these links will surely help to study and understand in a more fundamental way the common observation that eating healthy will keep you and your immune system healthy.

Figure 1

After a meal, fatty acids and glucose, through intestinal absorption, enter the blood. Both serve as fuels for cells or tissues, glucose being the most important to fulfill the energy requirement of immune cells, and lipids representing major components of cell membranes. Besides, food-derived fatty acids, as well as intestinal bacteria-derived fatty acids could be sensed by Toll-like receptors (TLRs) which are expressed on immune cells, adipocytes or intestinal gut, resulting in activation of the immune system. Depending on the intensity, the time lasting, and the control of these events, it will either favor the development of an efficient immune defense, or lead to a drift towards metabolic diseases such as obesity.