Effect of Green Tea Amino Acid L-Theanine on Physiological Responses: A Protocol for Clinical Trial

Abstract

Background and objectives: L-theanine (L-THE) is a green tea-derived amino acid, consumed for its many benefits, including improved cardiovascular health, anxiolytic effects, antioxidant properties, and its effect on instigating a state of relaxed alertness. The aim of this clinical trial is to evaluate the effectiveness of the amino acid L-THE embedded in functional food whey protein mango sorbet, its related stress effects on physiological responses, state of alertness, and focus, and the accuracy of eye movements post-consumption.Methods: Twenty-one healthy males, aged 18-65, will be recruited for this study. Participants will be required to consume a mango sorbet (without L-THE) and mango sorbet containing 0.2 g of L-THE and a placebo or 0.2 g pure L-THE within a capsule, after an overnight fast. L-THE exerts its effects 30-50 minutes post consumption, lasting up to 90 minutes. Participants will perform a series of visual functional tests, including habitual visual acuity, contrast sensitivity and measurements of saccadic eye movements after the consumption of the food products at 15-minute intervals to measure their state of alertness and fatigue. Salivary cortisol will be measured every 30 minutes; blood pressure, heart rate and heart rate variability responses will also be measured every 10 minutes.Discussion: The use of L-THE as a functional additive may provide potential therapeutic stress benefits when consumed alongside food products. The results of this protocol study will ultimately determine whether L-THE embedded within mango sorbet at physiologically relevant levels can alter the stress response and exhibit its effect on eye fatigue and concentration.