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Title: The effects of energy availability on bone metabolism and health
Author: Papageorgiou, M.
ISNI:       0000 0004 6352 3773
Awarding Body: Nottingham Trent University
Current Institution: Nottingham Trent University
Date of Award: 2016
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No experimental studies have been conducted on the impact of low EA on bone metabolism in relevant physically active populations. We evaluated the effects of low EA on bone turnover markers (BTMs) in a cohort of Caucasian, physically active eumenorrheic women (Study 1) and men (Study 2), and compared effects between sexes (sex comparison). These two studies were performed using a randomised, counterbalanced, crossover design. Eleven eumenorrheic women [peak aerobic capacity (VO2 peak): 47.9±5.5 ml·kg-1·min-1] and eleven men (VO2 peak: 54.2±5.3 ml·kg-1·min-1) completed two 5-day protocols; controlled (CON; 45 kcal·kgLBM-1·d-1) and restricted (RES; 15 kcal·kgLBM-1·d-1) EAs. Participants ran daily under supervision on a treadmill at 70% of their VO2 peak resulting in an exercise energy expenditure (EEE) of 15 kcal·kgLBM-1·d-1 and consumed diets providing 60 and 30 kcal·kgLBM-1·d-1 (based on participants’ habitual dietary composition). The effects of short-term (3 days) low EA induced by diet or exercise alone on BTMs in Caucasian, physically active eumenorrheic women (Study 3) and oral contraceptive (OCP) users were explored (Study 4), and compared effects between groups (comparison between eumenorrheic women and combined OCP users). Studies 3 and 4 were performed using a randomised, counterbalanced, crossover design. Ten eumenorrheic women (VO2 peak: 48.1 ±3.3 ml·kg-1·min-1) and 10 combined OCP users (VO2 peak: 47.9±5.5 ml·kg-1·min-1) completed three 3-day protocols; controlled (CON; 45 kcal·kgLBM-1·d-1) and restricted through diet (D-RES; 15 kcal·kgLBM-1·d-1) and restricted through exercise (E-RES; 15 kcal·kgLBM-1·d-1) EAs. In CON, D-RES and E-RES participants consumed diets providing 45, 15 and 45 kcal·kgLBM-1·d-1 with standardised composition (50% carbohydrates, 20% protein and 30% fat) in all experimental conditions. In E-RES only, participants completed supervised laboratory exercise sessions at an exercise intensity of 70% of their VO2 peak that resulted in an EEE of 30 kcal·kg LBM-1·d-1. Study 1: Short-term low EA at 15 kcal·kgLBM-1·d-1 decreased bone formation [Amino-terminal propeptide of type 1 procollagen (P1NP) AUC; P < 0.05] and increased bone resorption [Carboxyl-terminal cross-linked telopeptide of type I collagen (β-CTX) AUC; P < 0.05] in physically active, eumenorrheic women. Significant reductions in energy regulatory hormones; leptin, insulin and triiodothyronine (T3), but no changes in reproductive hormones or markers of calcium metabolism were shown. Study 2: In men, low EA at 15 kcal·kgLBM-1·d-1 had no significant effects on bone formation or bone resorption. Insulin growth factor 1 (IGF-1) was significantly reduced (P < 0.05), whereas regulatory hormones or markers of calcium metabolism were not affected. Sex comparison: No significant differences were shown between sexes, with the magnitude of the responses iv in all markers to low EA being similar in men and women. Study 3: Short-term diet-induced low EA (15 kcal·kgLBM-1·d-1) resulted in a reduction in bone turnover (BT) ratio (P < 0.05), despite no alterations in P1NP and β-CTX in eumenorrheic women. Exercise-induced low EA did not impact BTM responses. Between diet- and exercise-induced low EAs there were no differences in BTM responses. Both low EA were accompanied by reductions in IGF-1 and leptin; T3 was reduced following diet-induced low EA only and insulin decreased in exercise-induced low EA only. Study 4: Neither P1NP nor β-CTX were affected by low EA in combined OCP users. These effects were not different depending on whether low EA was diet- or exercise-induced. IGF-1 was reduced in the exercise-induced low EA only, T3 decreased following diet-induced low EA only and leptin decreased in response to both low EAs. The direct comparison between combined OCP users and eumeorrheic women revealed no differences in BTM responses to either diet- or exercise-induced low EA. These findings suggest that short-term low EA (achieved through a combination of dietary restriction and exercise) is critical for bone metabolism and health in physically active women, supporting the Female Athlete Triad and the RED-S models. Although our study in men does not support the RED-S models within the short timeframe of this study, our direct sex comparison suggests a similar relationship between low EA and bone metabolism in men EA relative to women. Low EA through diet or exercise does not affect bone metabolism, despite a reduction in regulatory hormones. Combined OCP use does not affect bone metabolism and health following short-term low EA. When compared to eumenorheic women, combined OCP users show similar BTM responses when exposed to the same dietary and exercise conditions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available