1. Introduction
milk, GI distress, flatulence, dehydration, fullness, gastrointestinal (GI) disorders
DEHYDRATION, HEAT, GI DISORDERS, GASTROINTESTINAL DISORDERS
Replacement of fluid losses (dehydration) during sports activities in the heat has been investigated with different beverages. Bovine milk has been recommended for post-exercise rehydration, but its use during exercise may provoke gastrointestinal disorders. This study compared voluntary fluid intake, hydration, and incidence and severity of gastrointestinal (GI) disorders during exercise in the heat under three conditions: no drink (ND), water (W), and skimmed lactose-free milk (SM). Sixteen physically active university students exercised at 32 °C and 70% RH for 90 min at 60–75% HRmax while drinking W or SM ad libitum, or ND assigned at random. A questionnaire explored possible GI disorders. Ad libitum intake was higher (Physically active humans generate large amounts of heat, some of which is dissipated to the environment by the evaporation of sweat. This sweat loss must be compensated by drinking enough fluid. In an attempt to meet the requirements for effective hydration, several different beverages have been studied. This includes juices [Milk, as a hydration beverage, offers several positive characteristics, such as a concentration of sodium and potassium within those recommended for sports drinks (10–35 mmol/L and 3–5 mmol/L, respectively) [Meanwhile, milk ingestion in adults has been shown to cause negative GI symptoms, such as fullness and flatulence, often blamed on the presence of lactose [The purpose of this study was, therefore, to compare voluntary fluid intake with water or lactose-free skim milk during moderate-intensity exercise in the heat, and to compare the resulting urine output and hydration effectiveness. The study also explored GI distress, comparing 19 upper tract, lower tract, and systemic GI symptoms under three conditions: water, milk, and no drink.