GLOSSARY

Gastrointestinal Distress During Exercise describes gastrointestinal symptoms occurring around exercise feeding. Intake, intensity, environment and underlying conditions can contribute together.

Gut training means practicing the intended food and fluid strategy during suitable training sessions and progressing according to tolerance. Repeated exposure may improve comfort or handling, but symptom improvement does not directly prove increased transporter expression in an individual. Glucose and fructose transport involve different proteins and their adaptation is a specific research question. Record actual intake, conditions and symptoms. A very high intake used successfully by one athlete should not be treated as the starting requirement for everyone.

Glucose and galactose use intestinal SGLT1 transport, while fructose uses GLUT5. Combining suitable carbohydrate sources can engage different absorption pathways and increase exogenous carbohydrate availability under relevant conditions. Maltodextrin yields glucose units during digestion rather than creating a separate fructose transport pathway. The blend, total intake, fluid provision, exercise and tolerance all matter. No single glucose-to-fructose ratio or hourly intake is a universally optimal prescription for every athlete and event.

Exogenous carbohydrate comes from food or drink, while endogenous carbohydrate comes from existing body stores. Digestion, intestinal absorption, circulation, muscle uptake and oxidation are separate steps. Tracer studies can estimate oxidation of ingested substrate under defined assumptions. The amount consumed is not the amount oxidized immediately, and a high measured oxidation rate does not alone prove better race performance. Specify the substrate source and the process measured before comparing research or planning intake.

Liquid, solid and semisolid sources can all contribute carbohydrate, with digestion and tolerance influenced by their composition and the exercise context. A drink may help combine fluid and fuel, while solid food can add variety during longer events. A concentrated gel may need to be coordinated with water according to its formulation and the plan. Combining forms should account for the total intake rather than counting each product in isolation or assuming liquid carbohydrate bypasses digestion and absorption limits.

For example, practice the intended carbohydrate source and amount during suitable sessions, recording symptoms and conditions. Progress according to tolerance instead of immediately copying a very high intake used by another athlete. Better comfort can be valuable without claiming that a specific intestinal transporter has been measured or increased in that individual.

Fluid planning should consider sweat losses, conditions, tolerance and opportunities to drink. Carbohydrate and fluid needs can differ, so a single beverage may not meet both without adjustment. Excessive drinking can also be harmful; more fluid is not always better. Sodium provision may be relevant in selected prolonged or high-loss situations, but it does not make unlimited drinking safe. Practice the combined food-and-fluid plan in training and evaluate actual intake and symptoms rather than relying only on a product label.

A fueling plan must survive practical constraints: carrying capacity, access to bottles, aid-station spacing, package opening, food safety and the opportunity to swallow while moving. Rehearsal helps identify a plan that is nutritionally adequate but impractical at race pace. Check what the event actually provides and prepare workable alternatives. Travel and tournaments can also change meal timing and food access. A slightly simpler plan followed consistently can be more useful than an ambitious calculation that cannot be executed.