Abstract
Thirteen female adolescent soccer players (14.3 ± 1.3 years) participated in a cross-over, double-blind trial examining the effects of Greek yogurt (GY) consumption on bone biomarkers during 5 days of intense soccer training. The study took place over two intervention weeks, which consisted of a pre-training assessment day, 5 training days, and a post-training assessment day. Participants completed the GY condition and a carbohydrate isocaloric placebo control pudding condition (CHO) in random order, 4 weeks apart. Morning, fasted, resting blood samples were collected pre- and post-training in each condition. Total osteocalcin (tOC), undercarboxylated osteocalcin (unOC), C-terminal telopeptide of type 1 collagen (CTX), osteoprotegerin (OPG), and receptor activator nuclear factor kappa-β ligand (RANKL) were measured in serum. The results showed no effects for time (pre- to post-training) or condition, and no interaction for tOC, CTX, OPG, RANKL, and the OPG/RANKL ratio. A time-by-condition interaction (p = 0.011) was observed in unOC, reflecting a post-training decrease in the GY, but not the CHO condition (−26% vs. −3%, respectively). However, relative unOC (% of tOC) decreased post-training (−16%), with no differences between conditions. These findings suggest that short-term high-impact intense training had no direct catabolic impact on bone metabolism, with GY adding no benefit beyond that of the isocaloric CHO control pudding.
Highlights
Adolescence is the period of life when the highest amounts of bone mass is accrued through an increase in bone formation, without which disease and chronic issues such as osteoporosis and chronic bone mineral deficiencies can occur later in life, especially for females [1]
As per the study design, participants consumed significantly more protein in the Greek yogurt (GY) condition compared to the CHO condition (p ≤ 0.001), and significantly more carbohydrates in the CHO condition compared to the GY condition (p ≤ 0.001), with no differences in daily energy or fat intake between GY and CHO (Table 2)
Habitual diet was assessed by food frequency questionnaire; energy and macronutrient consumption during the Greek yogurt (GY) and isocaloric control (CHO) conditions were assessed using diet records. * indicates GY significantly greater (p < 0.05) than CHO and habitual. † indicates CHO significantly greater (p < 0.05) than GY and habitual
Summary
Adolescence is the period of life when the highest amounts of bone mass is accrued through an increase in bone formation, without which disease and chronic issues such as osteoporosis and chronic bone mineral deficiencies can occur later in life, especially for females [1]. Longer periods of intense exercise could potentially lead to an uncoupling or imbalance of bone turnover, favoring increased bone resorption, which may have detrimental effects on bone mass and health [9]. Calcium consumption, whether lower or higher than the recommended intake, could exacerbate or counterbalance, respectively, any potentially negative effects of intense exercise on bone [15]. According to a recent study in adult male endurance athletes, a protein beverage combined with carbohydrates consumed immediately post-exercise resulted in increased circulating levels of bone formation markers, and decreased levels of bone resorption markers [17]. The protein requirements for child and adolescent athletes or highly active youth are still unspecified due to the lack of studies examining the effects of protein consumption on bone turnover in young athletes, who may have higher needs for protein than non-athletic youth
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