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The purpose of this study is to summarize water, carbohydrate (CHO), and electrolyte absorption from carbohydrate- electrolyte (CHO-E) solutions based on all of the triple-lumen-perfusion studies in humans since the early 1960s. The current statistical analysis included 30 reports from which were obtained information on water absorption, CHO absorption, total solute absorption, CHO concentration, CHO type, osmolality, sodium concentration, and sodium absorption in the different gut segments during exercise and at rest. Mean differences were assessed using independent-samples t tests. Exploratory multiple-regression analyses were conducted to create prediction models for intestinal water absorption. The factors influencing water and solute absorption are carefully evaluated and extensively discussed. The authors suggest that in the human proximal small intestine, water absorption is related to both total solute and CHO absorption; osmolality exerts various impacts on water absorption in the different segments; the multiple types of CHO in the ingested CHO-E solutions play a critical role in stimulating CHO, sodium, total solute, and water absorption; CHO concentration is negatively related to water absorption; and exercise may result in greater water absorption than rest. A potential regression model for predicting water absorption is also proposed for future research and practical application. In conclusion, water absorption in the human small intestine is influenced by osmolality, solute absorption, and the anatomical structures of gut segments. Multiple types of CHO in a CHO-E solution facilitate water absorption by stimulating CHO and solute absorption and lowering osmolality in the intestinal lumen.

Eight healthy subjects, aged 39.0 ± 2.4 years, consumed four 6% carbohydrate-electrolyte solutions containing either one (glucose or fructose) or two transportable carbohydrates in single (glucose + fructose) or bound (sucrose) forms. Solution osmolalities ranged from 250 to 434 mOsm/kg H₂O. The test solutions were ingested at rest in the amount of 6 ml/kg of body weight at a temperature of 12 °C. Gastric emptying rate was measured by repeated aspirations via a nasogastric tube using the modified George double-sampling technique. The intragastric temperature was determined by a temperature probe attached to the nasogastric tube. There were no significant differences in gastric emptying rates and gastric volumes among the solutions. Intragastric temperature dropped from 36.5 °C to 23.3±3 °C immediately after beverage ingestion but recovered to above 30 °C within 5 min. These data suggest that the gastric emptying rate of the specified beverages is not affected by the number and type of carbohydrates or by solution osmolalities within the tested range. Within 5 min after ingestion, cold beverages are warmed to above 30 °C in the stomach. This infers that the effect of cold solution temperature on gastric emptying rate is likely to be small and transitory.

The aim of this study was to compare daily hydration profiles of competitive adolescent swimmers and less active maturation- and sex-matched controls. Hydration profiles of 35 competitive adolescent swimmers (male n = 18, female n = 17) and 41 controls (male n = 29, female n = 12) were monitored on 4 consecutive days. First morning hydration status was determined independently by urine specific gravity (USG) and urine color. Changes in fluid balance were estimated during the school day and in training sessions after adjusting for self-reported urine losses and fluid intake. Urinalyses revealed consistent fluid deficits (USG >1.020, urine color ≥5) independent of activity group, sex, and day of testing (hypohydration in 73–85% of samples, p > .05). Fluid balance and intake were observed over typical school days in males and females from the 2 groups. During training, male swimmers lost more fluid relative to initial body mass but drank no more than females. Although both activity groups began each testing day with a similar hydration status, training induced significant variations in fluid balance in the swimmers compared with controls. Despite minimal fluid losses during individual training sessions (<2% body mass), these deficits significantly increased fluid needs for young swimmers over the school day.

This study investigated whether different beverage carbohydrate concentration and osmolality would provoke gastrointestinal (GI) discomfort during intermittent, high-intensity exercise. Thirty-six adult and adolescent athletes were tested on separate days in a double-blind, randomized trial of 6% and 8% carbohydrate-electrolytes (CHO-E) beverages during four 12-min quarters (Q) of circuit training that included intermittent sprints, lateral hops, shuttle runs, and vertical jumps. GI discomfort and fatigue surveys were completed before the first Q and immediately after each Q. All ratings of GI discomfort were modest throughout the study. The cumulative index for GI discomfort, however, was greater for the 8% CHO-E beverage than for the 6% CHO-E beverage at Q3 and Q4 (P < 0.05). Averaging across all 4 quarters, the 8% CHO-E treatment produced significantly higher mean ratings of stomach upset and side ache. In conclusion, higher CHO concentration and osmolality in an ingested beverage provokes stomach upset and side ache.