Periodisation – defined as the systematic planning and sequencing of training blocks across macro, meso and micro cycles of training and racing as a means to optimise athletic adaptation and performance – has been implemented by coaches to athletes across most sports for several decades. Similarly to training, nutrition should also be periodised to support training and racing goals. For example, the diets of endurance athletes may move along the spectrum from low to high energy availability (EA) or low to high carbohydrate (CHO) availability (e.g. body composition management with brief periods of low EA or CHO vs optimised adherence to sports nutrition guidelines via high energy and CHO availability). Despite robust evidence behind current guidelines, the literature lacks systematic information on the knowledge and implementation of periodised nutrition strategies across various levels of training and racing by world class endurance athletes. Another popular dietary approach – chronic or long-term ketogenic low-CHO, high fat (LCHF) diet – has become popular among some athletes and scientists as a means to enhance endurance performance and to support health. Notably, current literature does not support the former claim of enhanced performance, and the majority of existing evidence in favour of the latter claim comes from research in clinical populations (such as obesity, cancer, and epilepsy). Since endurance athletes are at an especially high risk for low bone mineral density (BMD) and stress fractures, and as available evidence suggests that both acute low EA and CHO availability may have independent and negative effects on bone modelling process in active individuals, this is an important topic that has been largely unexplored in the literature to-date. Therefore, this thesis will investigate dietary periodisation approaches in elite endurance athletes as well as the effects of low energy and low CHO availability on direct and indirect outcomes of markers of bone modelling and bone health in this population
