The purpose was to investigate the effects of a controlled typical 1-day diet supplemented with two different doses of whey protein isolate on blood amino acid profiles and hormonal concentrations following the final meal. Nine males (age: 29.6 ± 6.3 yrs) completed four conditions in random order: a control (C) condition of a typical mixed diet containing ~10% protein (0.8 g·kg–1), 65% carbohydrate, and 25% fat; a placebo (P) condition calorically matched with carbohydrate to the whey protein conditions; a low-dose condition of 0.8 grams of whey protein isolate per kilogram body mass per day (g·kg–1·d–1; W1) in addition to the typical mixed diet; or a high-dose condition of 1.6 g·kg–1·d–1 (W2) of supplemental whey protein in addition to the typical mixed diet. Following the final meal, significant (p < .05) increases in total amino acids, essential amino acids (EAA), branch-chained amino acids (BCAA), and leucine were observed in plasma with whey protein supplementation while no changes were observed in the control and placebo conditions. There was no significant group difference for glucose, insulin, testosterone, cortisol, or growth hormone. In conclusion, supplementing a typical daily food intake consisting of 0.8 g of protein·kg–1·d–1 with a whey protein isolate (an additional 0.8 or 1.6 g·kg–1·d–1) significantly elevated total amino acids, EAA, BCAA, and leucine but had no effect on glucose, insulin, testosterone, cortisol, or growth hormone following the final meal. Future acute and chronic supplementation research examining the physiological and health outcomes associated with elevated amino acid profiles is warranted.
Scott C. Forbes, Linda McCargar, Paul Jelen and Gordon J. Bell
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.
Whitney A. Welch, Scott J. Strath, Michael Brondino, Renee Walker and Ann M. Swartz
-by-breath data were averaged into 1-minute values. The Cosmed K4b 2 has shown to be a valid measure of oxygen uptake during exercise and rest, 14 , 15 showing small differences in oxygen consumption (VO 2 ), ranging from 0.088 to 0.092 L/min, when compared with the Douglas bag method. Mixed-Meal Tolerance Test
James R. Rowe, Kyle D. Biggerstaff, Vic Ben-Ezra, David L. Nichols and Nancy DiMarco
This study examined the effect of prior exercise on postprandial lipemia (PPL) concentration following a mixed meal (MM) made with either glucose or fructose. Sedentary women completed four trials in random order: 1) Rest-Fructose: RF, 2) Rest-Glucose: RG, 3) Exercise-Fructose: EF, 4) Exercise-Glucose: EG. Exercise expended 500 kcal while walking at 70%VO2max. Rest was 60 min of sitting. The morning after each trial, a fasting (12 hr) blood sample was collected followed by consumption of the MM. The MM was blended with whole milk and ice cream plus a glucose or fructose powder. Glucose and fructose powder accounted for 30% of the total kcal within the MM. Blood was collected periodically for 6 hr post-MM and analyzed for PPL. Magnitude of PPL over the 6 hr postmeal was quantified using the triglyceride incremental area under the curve (TG AUCI). Significant differences (p < .05) between trials were determined using repeated-measures ANOVA and Bonferroni post hoc test. There was no significant difference in the TG AUCI between the four trials (p > .05). A significant trial by time interaction for TG concentration was reported (p < .05). Despite lack of change in the AUCI with prior exercise, the lower TG concentration at multiple time points in the EG trial does indicate that prior exercise has some desirable effect on PPL. This study suggests that replacing fructose with glucose sugars and incorporating exercise may minimize PPL following a mixed meal but exercise will need to elicit greater energy expenditure.
Jennie A. Gilbert and James E. Misner
This study examined the metabolic response to a 763-kcal mixed meal at rest and during 30 min of exercise at 50% maximal oxygen consumption (
Timothy D. Heden, Ying Liu, Young-Min Park, Nathan C. Winn and Jill A. Kanaley
This study assessed if walking at a self-selected pace could improve postprandial glucose and insulin concentrations in obese adolescents consuming high-fructose (HF) or high-glucose (HG) diets.
Seven obese male and female adolescents (18 ± 1 yr) performed 4, 15-day trials in a random order, including 1) HF-diet (50 g fructose/d added to normal diet) while being sedentary, 2) HG-diet (50 g glucose/d) while sedentary, 3) HF-diet with additional walking, and 4) HG-diet with additional walking. On the 15th day of each trial, the participants performed mixed meal testing in the laboratory in which they consumed three liquid shakes (either HF or HG) and during the HF and HG sedentary trials, the participants took < 4000 steps while in the laboratory but during the walking trials took ≥ 13,000 steps during testing.
Walking did not alter postprandial glucose concentrations. Although walking reduced insulin secretion by 34% and 25% during the HF- and HG-diet, respectively (P < .05), total insulin concentrations were only significantly reduced (P > .05) with walking during the HF trial, possibly because walking enhanced insulin clearance to a greater extent during the HF-diet.
Walking reduces postprandial insulin secretion in obese adolescents consuming a high-fructose or high-glucose diet.
Stephen A. Mears, Kathryn Dickinson, Kurt Bergin-Taylor, Reagan Dee, Jack Kay and Lewis J. James
doi:10.1152/japplphysiol.90882.2008 10.1152/japplphysiol.90882.2008 13. Taylor R , Magnusson I , Rothman DL , et al . Direct assessment of liver glycogen storage by 13C nuclear magnetic resonance spectroscopy and regulation of glucose homeostasis after a mixed meal in normal subjects . J
Alaaddine El-Chab and Miriam E. Clegg
– 1047 . PubMed 10.1093/ajcn/48.4.1041 Wolever , T.M. , Nuttall , F.Q. , Lee , R. , Wong , G.S. , Josse , R.G. , Csima , A. , & Jenkins , D.J. ( 1985 ). Prediction of the relative blood glucose response of mixed meals using the white bread glycemic index . Diabetes Care, 8 ( 5 ), 418
Edward A. Gray, Thomas A. Green, James A. Betts and Javier T. Gonzalez
assessment of liver glycogen storage by 13C nuclear magnetic resonance spectroscopy and regulation of glucose homeostasis after a mixed meal in normal subjects . Journal of Clinical Investigation, 97, 126 – 132 . PubMed ID: 8550823 doi:10.1172/JCI118379 10.1172/JCI118379 Tsintzas , K. , & Williams
Dean Ritchie, Justin Keogh, Steven Stern, Peter Reaburn, Fergus O’Connor and Jonathan D. Bartlett
the season. Future research should aim to incorporate methods of RT performance such as body composition and repetition maximum testing to provide a broader overview of the effect of preceding endurance training. Further, while optimal nutrition (ie, a mixed meal providing ample amounts of