Muscle wasting is characterized by a loss of muscle mass and strength, and occurs in several pathological conditions such as cancer, chronic heart failure, chronic infection and malnutrition. Muscle wasting can be caused by inflammation and inappropriate nutritional status. Interestingly, gut microbiota has recently been proposed as an environmental factor involved, among others, in energy sparing from the diet, and in the regulation of host immunity and metabolism. This review presents evidence supporting the existence of a gut microbiota-muscle axis and discusses the potential role and therapeutic interest of gut microbiota in muscle wasting, specifically in the context of cancer and malnutrition. This review also proposes possible molecular mechanisms underlying the gut microbiota-muscle axis. This article is part of a Directed Issue entitled: Molecular basis of muscle wasting. Copyright © 2013 Elsevier Ltd. All rights reserved.