The plant extract guarana is known for its caffeine content and other bioactive ingredients, which purportedly may improve cognitive performance. Recent reviews have examined the effects of chronic supplementation of guarana in clinical populations; however, the acute effects of guarana on cognitive tasks, while of interest, have produced mixed results. Whether acute guarana ingestion improves human cognitive performance was assessed by performing a systematic review coupled with a meta-analysis. Eight placebo-controlled studies were identified and met the inclusion criteria providing data on 328 participants. The dose of guarana (37.5 to 500 mg) with reported caffeine content (4.3 to 100 mg) varied. Effect sizes (ESs) were calculated as the standardized mean difference and meta-analyses were completed using a random-effects model. The ESs for guarana averaged across a variety of cognitive measures and outcome variables were less than trivial (Hedge’s g = 0.076, p = 0.14). Using a subgroup meta-analysis (Q = 12.9, p < 0.001), ESs indicating a faster response time for guarana vs. a placebo (g = 0.202, p = 0.005) differed from the accuracy measures (g = −0.077, p = 0.4) which were non-significant. For response time, guarana ingested in a capsule (g = 0.111) tended to differ (Q = 2.96, p = 0.085) compared to guarana when dissolved in liquid (g = 0.281). Meta-regression of the study ESs of overall cognitive task performance was not related to the guarana dose (R2 < 0.001) or to the time allowed prior to cognitive testing (R2 < 0.001). Acute guarana ingestion had a small effect on the response time (faster performance) during a variety of cognitive tasks without affecting the accuracy. Whether the changes were linked to the caffeine content or other bioavailable substances in guarana is unknown. Additional studies that directly compare matched doses of caffeine versus guarana are needed to understand its effects on cognitive performance.
We thank Dr. Gurney for his interest and comment [...]
Comparing cumulative urine output relative to that elicited by water facilitates a comparison of the short-term hydration properties of beverages. This metric of fluid retention is termed the beverage hydration index (BHI). PURPOSE: To determine the additive effect of electrolytes with either carbohydrate or protein to beverages on BHI. METHODS: Seventeen healthy young adult women and men completed four beverage test sessions in randomized order: deionized water (W), electrolytes only (E), carbohydrate-electrolytes (C+E), and 2 g/L dipeptide (alanyl-glutamine)-electrolytes (AG+E). [Electrolyte] (Na + 19 mmol, K + 3 mmol) were equivalent across all beverages except W. Subjects reported at 0700 h following an overnight fast and a standardized hydration protocol as previously described. One liter of each beverage was consumed over 30 min, metered at 7.5 min intervals. Cumulative urine output, body mass and urine osmolality were obtained every 60 min through 240 min. Beverage palatability was assessed with visual analog scales. RESULTS: Compared to W, BHI was significantly (P < .05) higher for C+E at 120 min (1.15 ± 0.17) while BHI for E (1.12 ±0.25) and AG+E (1.10 ± 0.24) were not different (P > .05). BHI for AG+E (1.15 ± 0.20) was higher than W later at 240 min. No test beverages differed in BHI from each other at any time point; however, net fluid balance was lower (by 134 g) at 60 min with AG+E vs. C+E. AG+E elicited a higher overall urine osmolality by 127 mosmol/kg vs. W (268±25 mosmol/kg). Palatability scores for taste were lower for W vs. other beverages and stomach bloating higher for W vs. C+E and AG+E. CONCLUSIONS: The addition of electrolytes (in ranges typically found in sports drinks) to water did not significantly improve fluid retention. Compared to water, the timeline for improved fluid retention occurs earlier for carbohydrate sports drink than a protein beverage with similar electrolyte levels. However, there was no meaningful difference among drinks in hydration status when [electrolyte] were equivalent.
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