John O’Reilly

Glycaemic index, glycaemic load and exercise performance.

The concept of the glycaemic index (GI) was first introduced in the early 1980s as a method of functionally ranking carbohydrate foods based on their actual postprandial blood glucose response compared with a reference food (either glucose or white bread). Although the GI is a debatable topic among many exercise and health professionals, nutritional recommendations to improve exercise performance and enhance exercise capacity are regularly based on information related to the GI.Studies focusing on the consumption of a pre-exercise GI meal have provided evidence that a benefit exists in relation to endurance performance and substrate utilization when a low GI meal is compared with a high GI meal. However, other investigations have shown that when nutritional strategies incorporating GI are applied to multiple meals, there is no clear advantage to the athlete in terms of exercise performance and capacity. It has been suggested that carbohydrate ingestion during endurance exercise negates the effect of the consumption of pre-exercise GI meals.The glycaemic load (GL) is a relatively novel concept in the area of sports nutrition, and has not been widely investigated. Its premise is that the effect, if any, on exercise performance is determined by the overall glycaemic effect of a diet and not by the amount of carbohydrate alone. The claims for GL have been disputed by a number of sports nutrition specialists, and have gone largely unrecognized by professional and scientific bodies. Research on the effect of the GL on exercise performance and capacity is still at an early stage, but recent studies have shown that the concept may have some merit as far as sports nutrition is concerned. It has been suggested that the GL may be a better predictor of glycaemic responses than the GI alone.

Influence of adipose tissue mass on bone mass in an overweight or obese population: systematic review and meta-analysis

Context: The scientific literature shows conflicting evidence about the relationship between adiposity and bone mass in overweight and obese populations. Objective: The aim of this review was to quantify the correlation between adipose mass (absolute and relative) and bone mineral density (BMD) in overweight and obese populations. Data Sources: Three databases were searched electronically. In addition, reference lists of relevant articles were screened. Study Selection: A total of 16 studies, comprising 2587 participants and 75 correlation coefficients were selected for inclusion in the review. Data Extraction: Data were extracted from each study using a standardized form. Results: Multilevel modeling indicated opposing relationships between BMD and adiposity: absolute adiposity correlated positively, and relative adiposity negatively, with BMD. Sex and age were the primary moderators of these relationships. Strong evidence supported a negative relationship between relative adipose mass and BMD in men (R = −0.37; 95%CI, −0.57 to −0.12) and in those aged less than 25 years (R = −0.28; 95%CI, −0.45 to −0.08). Conclusion: To prevent bone loss in overweight and obese populations, nutrition‐ and exercise‐based interventions that focus on a controlled reduction of adipose mass with concomitant preservation of lean mass are recommended. Systematic Review Registration: PROSPERO no. CRD42015024313.

Effect of the glycemic index of pre-exercise snack bars on substrate utilization during subsequent exercise

Abstract Purpose: To investigate the effect of the glycemic index (GI) of pre-exercise snack bars on substrate utilization during subsequent moderate intensity exercise. Methods: Fourteen male participants (Age: 27 ± 5 yr; BMI: 22.5 ± 2.7 kg m−2; : 48.7 ± 6.1 mL kg−1 min−1) completed two trials in a randomized and counterbalanced crossover design. Two iso-caloric snack bars with different GI values (20, LGI versus 68, HGI) were provided to the participants. Ninety minutes later, all participants completed 45 minutes of ergometer cycling at 65% . Substrate utilization was measured using indirect calorimetry. Results: During exercise, higher fat oxidation and lower carbohydrate (CHO) oxidation were observed in the LGI trial (LGI versus HGI: CHO, 87.3 ± 20.1 versus 99.2 ± 19.0 g, p < 0.05; Fat, 15.0 ± 5.8 versus 9.7 ± 7.0 g, p < 0.05). Conclusion: Compared with an iso-caloric HGI snack bar, pre-exercise LGI snack bar consumption may facilitate a shift of substrate utilization from CHO to fat during subsequent moderate intensity exercise.

New insights in professional horse racing; “in-race” heart rate data, elevated fracture risk, hydration, nutritional and lifestyle analysis of elite professional jockeys

ABSTRACT Weight-making practices have been shown to impair musculoskeletal and physiological function of jockeys. This study investigated the “in-race” heart rate (HR) responses and hydration status during competitive racing, as well as selected physiological and lifestyle parameters of professional jockeys based in Hong Kong. “In-race” HR responses and early morning hydration status of 20 male jockeys were examined in hot and moderate climactic occasions. Additionally, bone mineral density (BMD), dietary intake and lifestyle choices were assessed. Osteopenia was observed in the calcanei of jockeys (left: 0.51 ± 0.06; right: 0.46 ± 0.12 g · cm−2). Energy and protein intake were significantly lower on a race day compared to a non-race day (P < 0.05). “In-race” HRmax values were similar to those from VO2max laboratory tests (186 ± 14 vs. 185 ± 8 bpm). Hypohydration was observed on both racing days. (USG: 1.0247 ± 0.006 and 1.0256 ± 0.0258 mg · L−1 for hot and moderate conditions, respectively). Sauna usage (25.5%) and food restriction (20.4%) were the most common weight-making practices. Current lifestyle choices of jockeys result in suboptimal bone health, hydration status and nutritional intake, which can significantly enhance the fracture risk. Further research should develop exercise and nutrition guidelines for optimising their skeletal health.