Emerging evidence of the relationship between fat-free mass and ghrelin, glucagon-like peptide-1, and peptide-YY

•Deficits and increases in fat-free mass are associated with appetite regulation.•Evidence points to a biological link between fat-free mass and peripheral appetite hormones.•There is a strong case for an inverse relationship between fat-free mass and ghrelin.•A clear relationship for peptide-YY and glucagon-like peptide-1 has yet to be confirmed. Historically, fat mass has been considered to have significant influence on human body energy homeostasis through its indirect relationship with appetite control. However, over the past decade, there has been a surge of evidence supporting the potential role of fat-free mass (FFM) in appetite control, and thus the regulatory involvement of FFM in appetite-related measures. Yet, the underlying biological mechanisms that explain the role of FFM in tonic/episodic appetite regulation remain unclear. Available evidence points to a biological link between FFM and peripheral appetite hormones; however, these relationships may be appetite hormone specific. Therefore, the purpose of this review was to present the potential relationship between FFM and appetite hormones, while also emphasizing that further research is needed to elucidate potential cause-effect. Overall, available evidence suggests the appetite stimulating hormone, ghrelin, has an inverse relationship with FFM. The relationship between FFM and the appetite suppression hormones, peptide tyrosine-tyrosine and glucagon-like peptide-1, has been relatively unexplored. The evidence presented in this review should encourage researchers, clinicians, and health professionals to consider investigating FFM maintenance as a suitable strategy during weight loss for improvements in appetite control.