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The Impact of a Short-Term Ketogenic Low-Carbohydrate High-Fat Diet on Biomarkers of Intestinal Epithelial Integrity and Gastrointestinal Symptoms

Alannah K.A. McKay, Alice M. Wallett, Andrew J. McKune, Julien D. Périard, Philo Saunders, Jamie Whitfield, Nicolin Tee, Ida A. Heikura, Megan L.R. Ross, Avish P. Sharma, Ricardo J.S. Costa, and Louise M. Burke

Endurance exercise can disturb intestinal epithelial integrity, leading to increased systemic indicators of cell injury, hyperpermeability, and pathogenic translocation. However, the interaction between exercise, diet, and gastrointestinal disturbance still warrants exploration. This study examined whether a 6-day dietary intervention influenced perturbations to intestinal epithelial disruption in response to a 25-km race walk. Twenty-eight male race walkers adhered to a high carbohydrate (CHO)/energy diet (65% CHO, energy availability = 40 kcal·kg FFM−1·day−1) for 6 days prior to a Baseline 25-km race walk. Athletes were then split into three subgroups: high CHO/energy diet (n = 10); low-CHO, high-fat diet (LCHF: n = 8; <50 g/day CHO, energy availability = 40 kcal·kg FFM−1·day−1); and low energy availability (n = 10; 65% CHO, energy availability = 15 kcal·kg FFM−1·day−1) for a further 6-day dietary intervention period prior to a second 25-km race walk (Adaptation). During both trials, venous blood was collected pre-, post-, and 1 hr postexercise and analyzed for markers of intestinal epithelial disruption. Intestinal fatty acid-binding protein concentration was significantly higher (twofold increase) in response to exercise during Adaptation compared to Baseline in the LCHF group (p = .001). Similar findings were observed for soluble CD14 (p < .001) and lipopolysaccharide-binding protein (p = .003), where postexercise concentrations were higher (53% and 36%, respectively) during Adaptation than Baseline in LCHF. No differences in high CHO/energy diet or low energy availability were apparent for any blood markers assessed (p > .05). A short-term LCHF diet increased intestinal epithelial cell injury in response to a 25-km race walk. No effect of low energy availability on gastrointestinal injury or symptoms was observed.

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Ergogenic Effects of Very Low to Moderate Doses of Caffeine on Vertical Jump Performance

Teppei Matsumura, Yuki Takamura, Kazushi Fukuzawa, Kazuya Nakagawa, Shunya Nonoyama, Keigo Tomoo, Hayato Tsukamoto, Yasushi Shinohara, Motoyuki Iemitsu, Akinori Nagano, Tadao Isaka, and Takeshi Hashimoto

Although the ergogenic effects of 3–6 mg/kg caffeine are widely accepted, the efficacy of low doses of caffeine has been discussed. However, it is unclear whether the ergogenic effects of caffeine on jump performance are dose responsive in a wide range of doses. This study aimed to examine the effect of very low (1 mg/kg) to moderate doses of caffeine, including commonly utilized ergogenic doses (i.e., 3 and 6 mg/kg), on vertical jump performance. A total of 32 well-trained collegiate sprinters and jumpers performed countermovement jumps and squat jumps three times each in a double-blind, counterbalanced, randomized, crossover design. Participants ingested a placebo or 1, 3, or 6 mg/kg caffeine 60 min before jumping. Compared with the placebo, 6 mg/kg caffeine significantly enhanced countermovement jump (p < .001) and squat jump (p = .012) heights; furthermore, 1 and 3 mg/kg of caffeine also significantly increased countermovement jump height (1 mg/kg: p = .002, 3 mg/kg: p < .001) but not squat jump height (1 mg/kg: p = .436, 3 mg/kg: p = .054). There were no significant differences among all caffeine doses in both jumps (all p > .05). In conclusion, even at a dose as low as 1 mg/kg, caffeine improved vertical jump performance in a dose-independent manner. This study provides new insight into the applicability and feasibility of 1 mg/kg caffeine as a safe and effective ergogenic strategy for jump performance.

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Erratum. Ergogenic Effects of Very Low to Moderate Doses of Caffeine on Vertical Jump Performance

International Journal of Sport Nutrition and Exercise Metabolism

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Stop, Collaborate, and Listen

James A. Betts

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Erratum. The Postprandial Plasma Amino Acid Response Does Not Differ Following the Ingestion of a Solid Versus a Liquid Milk Protein Product in Healthy Adult Females

International Journal of Sport Nutrition and Exercise Metabolism

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The Postprandial Plasma Amino Acid Response Does Not Differ Following the Ingestion of a Solid Versus a Liquid Milk Protein Product in Healthy Adult Females

Glenn A.A. van Lieshout, Jorn Trommelen, Jean Nyakayiru, Janneau van Kranenburg, Joan M. Senden, Lex B. Verdijk, and Luc J.C. van Loon

Dietary protein digestion and amino acid absorption rates are modulated by numerous factors such as the food matrix. It has been speculated that protein ingested in liquid form is more rapidly digested and absorbed when compared with ingestion in solid form. Here, we assessed the postprandial plasma amino acid availability following ingestion of a single bolus of protein provided in either liquid or solid form. Twelve healthy, young females were included in this randomized cross-over study. On two separate test days, participants ingested 20-g milk protein concentrate in solid form (protein bar) or in liquid form (protein drink). Products were composed of matched ingredients and, thereby, had the same macro- and micronutrient composition. On both test days, arterialized blood samples were collected at regular time intervals for up to 4 hr following protein ingestion to assess the postprandial rise in plasma amino acid concentrations. Protein ingestion robustly elevated circulating plasma amino acid concentrations (p < .001), with no significant differences between treatments (p = .088). The incremental area under the curve of the postprandial rise in total plasma amino acid concentrations did not differ following bar versus drink consumption (160 ± 73 vs. 160 ± 71 mmol·L−1·240 min−1, respectively; 95% confidence interval [−37, 37]; Cohen’s d z  = 0.003; p = .992). Ingestion of protein in liquid or solid form does not modulate postprandial amino acid availability in healthy, female adults. Any differences in protein digestion and amino acid absorption due to differences in food matrix are not attributed to the protein being consumed as a bar or as a drink.

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Effect of a 24-Week Concurrent Exercise Intervention on Neck Adiposity and Its Distribution in Young Adults: The ACTIBATE Randomized Controlled Trial

Maria Jose Arias-Tellez, Francisco M. Acosta, Elisa Merchan-Ramirez, Borja Martínez-Téllez, Guillermo-Sánchez Delgado, Jose M. Llamas-Elvira, and Jonatan R. Ruiz

Neck adipose tissue (NAT) accumulation and neck circumference are independent predictors of cardiometabolic risk (CMR) and low-grade chronic inflammation in young adults. The present study examines whether a 24-week concurrent exercise intervention can reduce NAT volume and neck circumference in young adults, and whether any changes in these variables are related to changes in body composition, CMR, and the inflammatory profile. Seventy-four participants (51 women, age 22 ± 2 years) were included in the main analyses, after being randomly assigned to either a (a) control (n = 34), (b) moderate-intensity exercise (n = 19), or (c) vigorous-intensity exercise (n = 21) group. Participants in the exercise groups trained 3–4 days/week (endurance + resistance exercise training). NAT volume and NAT distribution across different depots were estimated using computed tomography before and after the intervention. Anthropometric variables, body composition (determined by dual-energy X-ray absorptiometry), and CMR/inflammatory markers were also recorded. The exercise intervention did not reduce the total NAT volume, nor was NAT distribution affected (p > .05). However, it did reduce neck circumference in the vigorous-intensity exercise group compared with the moderate-intensity exercise and control groups (by 0.8 and 1 cm, respectively, p ≤ .05). Changes in total NAT and neck circumference were positively, albeit weakly, related (adj. R 2: .05–.21, all p ≤ .05) to changes in body weight and adiposity, leptin (only total NAT), and CMR (only neck circumference). Altogether 24 weeks of concurrent exercise does not appear to reduce NAT accumulation in young adults, but may slightly reduce neck circumference in those who partake in vigorous exercise.

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Erratum. CYP1A2 Genotype Polymorphism Influences the Effect of Caffeine on Anaerobic Performance in Trained Males

International Journal of Sport Nutrition & Exercise Metabolism

Open access

Amino Acid-Based Beverage Interventions Ameliorate Exercise-Induced Gastrointestinal Syndrome in Response to Exertional-Heat Stress: The Heat Exertion Amino Acid Technology (HEAAT) Study

Ricardo J.S. Costa, Kayla Henningsen, Stephanie K. Gaskell, Rebekah Alcock, Alice Mika, Christopher Rauch, Samuel N. Cheuvront, Phil Blazy, and Robert Kenefick

The study aimed to determine the effects of two differing amino acid beverage interventions on biomarkers of intestinal epithelial integrity and systemic inflammation in response to an exertional-heat stress challenge. One week after the initial assessment, participants (n = 20) were randomly allocated to complete two exertional-heat stress trials, with at least 1 week washout. Trials included a water control trial (CON), and one of two possible amino acid beverage intervention trials (VS001 or VS006). On VS001 (4.5 g/L) and VS006 (6.4 g/L), participants were asked to consume two 237-ml prefabricated doses daily for 7 days before the exertional-heat stress, and one 237-ml dose immediately before, and every 20 min during 2-hr running at 60% maximal oxygen uptake in 35 °C ambient conditions. A water volume equivalent was provided on CON. Whole blood samples were collected pre-, immediately post-, 1 and 2 hr postexercise, and analyzed for plasma concentrations of cortisol, intestinal fatty acid protein, soluble CD14, and immunoglobulin M (IgM) by ELISA, and systemic inflammatory cytokines by multiplex. Preexercise resting biomarker concentrations for all variables did not significantly differ between trials (p > .05). A lower response magnitude for intestinal fatty acid protein (mean [95% CI]: 249 [60, 437] pg/ml, 900 [464, 1,336] pg/ml), soluble CD14 (−93 [−458, 272] ng/ml, 12 [−174, 197] ng/ml), and IgM (−6.5 [−23.0, 9.9] MMU/ml, −10.4 [−16.2, 4.7] MMU/ml) were observed on VS001 and V006 compared with CON (p < .05), respectively. Systemic inflammatory response profile was lower on VS001, but not VS006, versus CON (p < .05). Total gastrointestinal symptoms did not significantly differ between trials. Amino acid beverages’ consumption (i.e., 4.5–6.4 g/L), twice daily for 7 days, immediately before, and during exertional-heat stress ameliorated intestinal epithelial integrity and systemic inflammatory perturbations associated with exercising in the heat, but without exacerbating gastrointestinal symptoms.

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Characterizing Hydration Practices in Healthy Young Recreationally Active Adults—Is There Utility in First Morning Urine Sampling?

Colleen X. Muñoz and Michael F. Bergeron

First morning urine (FMU) assessment would be a practical and convenient solution for clinically acceptable detection of underhydration prior to competition/training, and for the general public. Thus, we thus sought to determine the diagnostic accuracy of FMU as a valid indicator of recent (previous 24 hr, 5 days average) hydration practices. For 5 consecutive days and one final morning, 67 healthy women (n = 38) and men (n = 29; age: 20 [1] years, body mass index: 25.9 [5.5]) completed 24-hr diet logs for total water intake (from beverages and foods, absolute and relative to body mass), 24-hr urine and FMU collection (last morning only) for osmolality (Osm), specific gravity (SG), and color (Col), and morning blood sampling for plasma osmolality and copeptin. Correlations determined significance and relationship strength among FMU and all other variables. Area under the receiver operating characteristic curves, sensitivity, specificity, and positive likelihood ratios were employed using previously reported values to indicate underhydration (total water intake < 30 ml/kg, osmolality > 500, and >800 mOsm/kg, specific gravity > 1.017, and copeptin > 6.93 pmol/L). FMU_Osm and FMU_SG were significantly correlated (p < .05) to all variables except the previous 5-day plasma osmolality. FMU_Col was only significantly correlated with other color time intervals and total water intake per gram. FMU_Osm held greatest utility (area under the receiver operating characteristic curve, sensitivity, and specificity >80%) overall, with the best outcome being FMU_Osm indicating a previous 24-hr osmolality threshold of 500 mOsm/kg (FMU_Osm criterion >710 mOsm/kg and positive likelihood ratio = 5.9). With less effort and cost restriction, FMU is a viable metric to assess underhydration.