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Emma Stevenson, Clyde Williams, Maria Nute, Peter Swaile and Monica Tsui

The present study investigated the effect of the glycemic index of an evening meal on responses to a standard high glycemic index (HGI) breakfast the following morning. The metabolic responses to exercise 3 h after breakfast were also investigated. Seven active males completed 2 trials. In each trial, participants were provided with an evening meal on day 1, which was composed of either HGI or LGI (high or low glycemic index) carbohydrates. On day 2, participants were provided with a standard HGI breakfast and then performed a 60 min run at 65% VO2max 3 h later. Plasma glucose and serum insulin concentrations following breakfast were higher in the HGI trial compared to the LGI trial (P < 0.05). During exercise, there were no differences in substrate utilization. The results suggest that consuming a single LGI evening meal can improve glucose tolerance at breakfast but the metabolic responses to subsequent exercise were not affected.

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Emma Stevenson, Clyde Williams and Helen Biscoe

This study investigated the metabolic responses to high glycemic index (HGI) or low glycemic index (LGI) meals consumed during recovery from prolonged exercise. Eight male, trained athletes undertook 2 trials. Following an overnight fast, subjects completed a 90-min run at 70% VO2max. Meals were provided 30 min and 2 h following cessation of exercise. The plasma glucose responses to both meals were greater in the HGI trial compared to the LGI trial (P < 0.05). Following breakfast, there were no differences in the serum insulin concentrations between the trials; however, following lunch, concentrations were higher in the HGI trial compared to the LGI trial (P < 0.05). This suggests that the glycemic index of the carbohydrates consumed during the immediate post-exercise period might not be important as long as sufficient carbohydrate is consumed. The high insulin concentrations following a HGI meal later in the recovery period could facilitate further muscle glycogen resynthesis.

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Vandre C. Figueiredo, Michelle M. Farnfield, Megan L.R. Ross, Petra Gran, Shona L. Halson, Jonathan M. Peake, David Cameron-Smith and James F. Markworth

. Thus, it remains possible that following intensive resistance exercise that CHO-induced hyperinsulinemia may acutely activate further key translation initiation machinery within skeletal muscle compared with exercise alone. However, to date, such a hypothesis has not been experimentally tested

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John G. Seifert, Greg L. Paul, Dennis E. Eddy and Robert Murray

The effects of preexercise hyperinsulinemia on exercising plasma glucose, plasma insulin, and metabolic responses were assessed during 50 min cycling at 62% VO2max. Subjects were fed a 6% sucrose/glucose solution (LCHO) or a 20% maltodextrin/glucose solution (HCHO) to induce changes in plasma insulin. During exercise, subjects assessed perceived nauseousness and lightheadedness. By the start of exercise, plasma glucose and plasma insulin had increased. In the LCHO trial, plasma glucose values significantly decreased below the baseline value at 30 min of exercise. However, by 40 min, exercise plasma glucose and insulin values were similar to the baseline value. Exercise plasma glucose and insulin did not differ from baseline values in the HCHO trial. Ingestion of LCHO or HCHO was not associated with nausea or lightheadedness. It was concluded that the hyperinsulinemia induced by preexercise feediigs of CHO did not result in frank hypoglycemia or adversely affect sensory or physiological responses during 50 min of moderate-intensity cycling.

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Sofiya Alhassan and Thomas N. Robinson

Background:

Receiver operating characteristic (ROC) analysis is a common method used in diagnostic and screening tests to define thresholds levels of a factor that discriminates between 2 levels of another factor. The purpose of this analysis was to use ROC analysis to determine the optimal accelerometer-measured physical activity (PA) thresholds for predicting selective cardiovascular disease (CVD) risk factors.

Methods:

ROC was performed using data from Stanford Girls Health Enrichment Multisite Studies trial. PA was assessed for multiple days using accelerometers. CVD variables were overweight, elevated triglyceride, reduced HDL-C, hypertension, impaired fasting glucose, fasting insulin, and clustering of multiple CVD risk factors.

Results:

A sample of 261 girls participated, of which 208 had complete CVD risk measures (mean ± SD age = 9.4 ± 0.9yrs, BMI = 20.7 ± 4.8kg/m2). An average of ≥11.1 minutes/day at ≥2,600 counts/min was the maximally sensitive and specific threshold for discriminating girls who were overweight, ≥16.6 minutes/day at ≥2,000 counts/min for hyperinsulinemia or with ≥2 CVD risk factors. The Area Under the Curve for overweight, hyperinsulinemia, and ≥2 CVD risk factors was of 0.66, 0.58, and 0.60, respectively. The sensitivity and specificity associated with overweight, hyperinsulinemia, and ≥2 CVD risk factors were 60.3% and 72.9%, 53.3% and 83.9%, 44.0% and 84.7%, respectively.

Conclusion:

Empirically-derived thresholds of PA to optimally discriminate between girls with and without CVD risk were lower in this sample than generally recommended. This ROC approach should be repeated in other populations to determine optimal PA thresholds with clinical validity for research, surveillance and program evaluation.

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Robert R. Wolfe

We propose that there is a link between muscle protein synthesis and breakdown that is regulated, in part, through maintenance of the free intracellular pool of essential amino acids. For example, we propose that muscle protein breakdown is paradoxically elevated in the anabolic state following resistance exercise in part because the even greater stimulation of synthesis would otherwise deplete this pool. Thus, factors regulating muscle protein breakdown must be evaluated in the context of the prevailing rate of muscle protein synthesis. Further, the direct effect of factors on breakdown may depend on the physiological state. For example, local hyperinsulinemia suppresses accelerated muscle protein breakdown after exercise, but not normal resting breakdown. Thus, factors regulating muscle protein breakdown in human subjects are complex and interactive.

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Shane Bilsborough and Neil Mann

Considerable debate has taken place over the safety and validity of increased protein intakes for both weight control and muscle synthesis. The advice to consume diets high in protein by some health professionals, media and popular diet books is given despite a lack of scientific data on the safety of increasing protein consumption. The key issues are the rate at which the gastrointestinal tract can absorb amino acids from dietary proteins (1.3 to 10 g/h) and the liver’s capacity to deaminate proteins and produce urea for excretion of excess nitrogen. The accepted level of protein requirement of 0.8g · kg−1 · d−1 is based on structural requirements and ignores the use of protein for energy metabolism. High protein diets on the other hand advocate excessive levels of protein intake on the order of 200 to 400 g/d, which can equate to levels of approximately 5 g · kg−1 · d−1, which may exceed the liver’s capacity to convert excess nitrogen to urea. Dangers of excessive protein, defined as when protein constitutes > 35% of total energy intake, include hyperaminoacidemia, hyperammonemia, hyperinsulinemia nausea, diarrhea, and even death (the “rabbit starvation syndrome”). The three different measures of defining protein intake, which should be viewed together are: absolute intake (g/d), intake related to body weight (g · kg−1 · d−1) and intake as a fraction of total energy (percent energy). A suggested maximum protein intake based on bodily needs, weight control evidence, and avoiding protein toxicity would be approximately of 25% of energy requirements at approximately 2 to 2.5 g · kg−1 · d−1, corresponding to 176 g protein per day for an 80 kg individual on a 12,000kJ/d diet. This is well below the theoretical maximum safe intake range for an 80 kg person (285 to 365 g/d).

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Fernando S. Lobo, Andreia C.C. Queiroz, Natan D. Silva Junior, Fabio L. Medina, Luiz A.R. Costa, Tais Tinucci and Claudia L.M. Forjaz

 al . Postexercise responses of muscle sympathetic nerve activity and blood flow to hyperinsulinemia in humans . J Appl Physiol . 1999 ; 87 ( 2 ): 824 – 829 . PubMed ID: 10444645 doi:10.1152/jappl.1999.87.2.824 10.1152/jappl.1999.87.2.824 10444645 30. Halliwill JR , Dinenno FA , Dietz NM . Alpha

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Renato Sobral Monteiro-Junior, Paulo de Tarso Maciel-Pinheiro, Eduardo da Matta Mello Portugal, Luiz Felipe da Silva Figueiredo, Rodrigo Terra, Lara S. F. Carneiro, Vinícius Dias Rodrigues, Osvaldo J. M. Nascimento, Andrea Camaz Deslandes and Jerson Laks

RK , Weaver JA , et al . Human aging is associated with altered TNF-α production during hyperglycemia and hyperinsulinemia . Am J Physiol Endocrinol Metab . 2001 ; 281 : E1137 – 1143 . PubMed 10.1152/ajpendo.2001.281.6.E1137 11701426 51. Busquets N , Carmona L , Surís X . Revisión

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Rachel B. Parks, Hector F. Angus, Douglas S. King and Rick L. Sharp

hyperinsulinemia who would benefit from more stable blood glucose during exercise. Acknowledgments The authors would like to thank Jin Xing, Yulong Li, Elizabeth Gerdis, Emily Meese, Janelle Davis, and Collin Fett for their assistance with data collection. References Baur , D.A. , Vargas , F.C.S. , Bach , C