Since the passage of Title IX in 1972, which emphasised the importance of equal opportunity for sports participation regardless of gender, the involvement of women in sports has increased [1]. Sports participation and physical activity have been associated with many benefits, including improved self-esteem and body image, decreased obesity, and enhanced psychological and social health outcomes [2], [3], [4], [5].

Along with the many benefits of sporting activity, it seems that female athletes may experience symptoms related to a condition called the female athlete triad (the triad). The triad is a condition that refers to the interrelatedness of energy availability (EA) with or without disordered eating/eating disorder, menstrual irregularities, and low bone mineral density (BMD) [6], [7].

In 1997, the American College of Sports Medicine (ACSM) published their first position stand about the triad [8], which was then updated and replaced by the ACSM in 2007 [9]. In this update, the triad was recognised as a pathological position along the spectrum of the interrelationship between energy availability, menstrual function and bone mineral density. Therefore, according to the ACSM, a female athlete with the triad may not exhibit all of the clinical conditions (eating disorder, amenorrhea and osteoporosis) simultaneously.

Since 2007, the aetiological factor that has been shown to underpin the female athlete triad is an energy deficiency relative to the balance between dietary energy intake (EI) and the energy expenditure required for supporting a range of body functions, e.g., homoeostasis, health, growth, daily living and sporting activities [10]. Low EA which could be caused by EI reduction and/or increased exercise load, results in body system adjustments to decrease energy expenditure, thereby creating a disruption of the hormonal, metabolic and functional characteristics [10], [11]. Various causes of LEA have been suggested, including DE which has a complex and multifactorial pathogenesis and is considered a stress-related disorder [12].

Given the increasing rate of female athletes’ participation in sports, it is timely to examine the prevalence of the triad and its three conditions based on previously published observational studies. An accurate estimation of the prevalence of the triad in female athletes will help to further raise awareness of the problem and could ultimately lead to the prevention or early identification of it. To the best of our knowledge, there is no existing systematic review of population-based studies assessing the prevalence of the female athlete triad in adult female athletes. Therefore, the aim of this systematic review was to assess the prevalence of the pathological conditions of the female athlete triad (low energy availability [with or without DE], menstrual dysfunction and low bone mineral density) in adult female athletes.