title: Patterns of energy availability in free-living athletes and the physiological effects of controlled low energy availability in males
Creators: name: Taylor, HL
Publisher: name: Liverpool John Moores University
Year: 2026

description: The physiological effects of short-term low energy availability have been characterised in females; however, the responses of males are less well understood. The aim of this thesis was to examine the daily patterns of energy availability in free-living athletes and subsequently, to determine the endocrine, metabolic, and physiological effects of low energy and low carbohydrate availability under controlled experimental conditions in males. Study 1 demonstrated that elite male road cyclists only partially compensate for greater daily exercise energy expenditure levels with increasing energy intake, leading to a fluctuating pattern of daily energy availability across a week of free-living training during pre-season. These findings provide novel insights into ecologically valid patterns of energy availability for experimental research. Study 2 investigated the physiological effects of low energy availability under controlled experimental conditions using a heterogenous pattern of daily energy availability. Energy availability was reduced from 45 to 10 kcal•kg FFM¯¹•day¯¹ for five days, with concomitant aerobic exercise. Low energy availability elicited changes in endocrine, metabolic, and physiological markers indicative of energy preserving mechanisms in healthy, active males. Circulating glycerol, NEFA, and D-3-hydroxybutyrate concentrations increased and triiodothyronine, leptin, and IGF-1 concentrations reduced in response to low energy availability. Concentrations of bone resorption marker ß-CTx increased and of bone formation marker P1NP reduced during low energy availability. Total testosterone concentrations and rates of muscle protein synthesis were unaffected by low energy availability. The findings of this study demonstrate that exercising males are sensitive to the effects of short-term low energy availability in a similar manner to that reported in females. Study 3 investigated the endocrine, metabolic, and physiological effects of reduced carbohydrate availability under conditions of energy balance. Reducing carbohydrate intake from 7.7 to 1.5 g•kg¯¹•day¯¹, with an energy availability of 45 kcal•kg FFM¯¹•day¯¹, for four days led to increased circulating glycerol, non-esterified fatty acid, and D-3-hydroxybutyrate concentrations, in healthy active males. Concentrations of bone resorption marker ß-CTx increased with low carbohydrate availability, but bone formation marker P1NP concentrations were unchanged. Further markers of energy preservation typically associated with low energy availability, including triiodothyronine, leptin, insulin, and resting metabolic rate were unchanged by low carbohydrate availability. The findings of this study support the notion that bone metabolism may be affected by carbohydrate availability. Further endocrine, metabolic, and physiological responses typically associated with low energy availability appear sensitive to energy itself, rather than carbohydrate availability. In summary, free-living athletes experience heterogenous patterns of daily energy availability that have not been reflected in laboratory-based low energy availability research to-date. Low energy availability in males elicited endocrine, metabolic, and physiological changes indicative of energy preservation, similar to previously characterised in females. Some of these observed effects, such as changes in bone metabolism, may be mediated by carbohydrate availability. Whether the physiological effects of short-term low energy availability are predictive of long-term health and performance consequences requires further research.