Identifying and Analyzing Low Energy Availability in Athletes: The Role of Biomarkers and Red Blood Cell Turnover

Abstract

Low energy availability (LEA) is a growing concern that can lead to several problems for athletes. However, adaptation to LEA occurs to maintain balance over time, making diagnosis difficult. In this review, we categorize LEA into two phases: the initial phase leading to adaptation and the phase in which adaptation is achieved and maintained. We review the influence of LEA on sports performance and health and discuss biomarkers for diagnosing LEA in each phase. This review also proposes future research topics for diagnosing LEA, with an emphasis on the recently discovered association between red blood cell turnover and LEA.

Keywords: erythrocyte; erythropoiesis; female athlete triad; hemoglobin; resting metabolic ratio; serum iron.

Figure 1

Concept of acute and chronic low energy availability Initially, energy availability (EA; orange box) is sufficient to maintain energy balance (leftmost bar). When energy intake and non-exercise activity thermogenesis (NEAT; gray box) are constant and exercise energy expenditure (white dashed box) increases (red arrow), low energy availability (LEA) occurs, and energy balance becomes negative: this is the onset of acute LEA (second left bar). As this state persists, adaptation occurs and resting metabolic rate (RMR) and diet-induced thermogenesis (DIT) (cumulative green box) gradually decrease (green dashed line), and the body attempts to maintain energy balance (red dashed line). Eventually, adaptation to the LEA state is achieved to maintain apparent energy balance while suppressing RMR and DIT (rightmost bar). However, it is not yet clear how many days it takes to achieve adaptation and what conditions are sufficient to diagnose adaptation as achieved (chronic LEA).