Journal Title (Medline/Pubmed accepted abbreviation): Int J Sport Nutr Exerc Metab
Page numbers: 427-442
doi (if applicable): N/A
Article type: Review
Summary of article:
Intestinal fluid and nutrient absorption has been investigated in humans at rest and during exercise using a triple-lumen tube intubation perfusion technique beginning in the early 1960s. The triple-lumen tube intubation-perfusion technique provides a precise measurement of transport rate of water and solute in vivo at a specific intestinal site. The authors undertook an extensive literature search 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. Although this technique has been recognized as a gold standard for measuring intestinal water and solute absorption and is extensively used by many investigators to study intestinal transport mechanisms, gut permeability, and the efficacy of oral rehydration solutions (ORS) and sports drinks, there are still some limitations under certain conditions, such as bypassing gastric emptying, not measuring transport of the solution being perfused, and absorption of “nonabsorbed” marker. Because of the time, expense, and complexity of this system, no one laboratory has been able to investigate the full range of conditions that may be critical to understanding water and solute absorption. The authors considered the full range of published experimental findings from studies of human intestinal triple-lumen perfusion with CHO-E solutions and, using simple statistical regression techniques, integrated the data into models that suggest the critical factors involved in water absorption in the different gut segments and conditions. Based on their review, the authors suggest that in the human proximal small intestine, water absorption is related to both total solute and CHO absorption:
- Osmolality exerts various effects 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.
- Exercise may result in greater water absorption than rest.
A potential regression model for predicting water absorption is also proposed, and the credibility of the proposed model was verified by comparing predicted water absorption values with the actual values from the experiments.
Interpretation of findings/Key practice applications:
Rapid and effective rehydration should be the major function of ORS and sports drinks to promote optimal performance during exercise and also in cases where dehydration is induced by diarrhea. Based on an extensive review of the literature, water absorption from a CHO-E solution in the human small intestine is influenced by solution CHO concentration, CHO type, number of transportable CHOs (single vs multiple), osmolality, different segments of the small intestine, and exercise. These factors exert a significant effect on water absorption independently and/or interactively. Although some potential or proposed mechanisms for water and solute absorption are discussed, more studies in this area are needed for a better understanding of water and solute absorption associated with these influencing factors in different regions of the small intestine. The authors did not make any specific recommendations regarding composition of CHO-E solutions.