Considering the recent growth of exercise gastroenterology research focusing on exercise-induced gastrointestinal syndrome mechanisms, response magnitude, prevention and management strategies, the standardized assessment of gastrointestinal symptoms (GIS) is warranted. The current methodological study aimed to test the reliability of a modified visual analog scale for assessing GIS during exercise, in response to a variety of exertional-stress scenarios, with and without dietary intervention. Recreational endurance runners (n = 31) performed one of the three exercise protocols, which included: 2-hr running at 70% $\dot{\mathrm{V}}{\mathrm{O}}_2\max$ in temperate (24.7 °C) ambient conditions, with fluid restriction; 2-hr running at 60% $\dot{\mathrm{V}}{\mathrm{O}}_2\max$ in hot (35.1 °C) ambient conditions, while consuming chilled water immediately before and every 15 min during exercise; and 2-hr running at 60% $\dot{\mathrm{V}}{\mathrm{O}}_2\max$ in temperate (23.0 °C) ambient conditions, while consuming 30 g/20 min carbohydrate (2∶1 glucose∶fructose, 10% temperate w/v), followed by a 1-hr distance test. GIS was monitored pre-exercise, periodically during exercise, and immediately postexercise. After wash out, participants were retested in mirrored conditions. No significant differences (p > .05) were identified between test–retest using Wilcoxon signed-rank test for all GIS (specific and categorized), within each exercise protocol and the combined protocols. Strong correlations were observed for gut discomfort, total GIS, upper GIS, and nausea (r_s = .566 to r_s = .686; p < .001), but not for lower GIS (r_s = .204; p = .232). Cohen’s magnitude of difference was minimal for all GIS (specific δ < 0.14 and categorized δ < 0.08). The modified visual analog scale for assessing GIS during exercise appears to be a reliable tool for identifying incidence and severity of GIS in cohort populations and is sensitive enough to detect exertional and intervention differences.