A study from the Journal of the American College of Nutrition (JACN) discusses fluid intake adequacy in detail and a simple tool is reviewed that may help healthy, active, low-risk populations answer the question, "Am I drinking enough?" The article "Am I Drinking Enough? Yes, No, and Maybe" by Samuel N. Cheuvront PhD, RD and Robert W. Kenefick PhD is made available with Free Access in JACN Issue 35(2) 2016, the official publication of the American College of Nutrition.
Adequacy of fluid intake for replacing meaningful water losses (dehydration) can be assessed simply, inexpensively, and with reasonable fidelity among healthy, active, low-risk individuals. A wide range of fluid intakes are compatible with euhydration (drinking enough), whereby total body water varies narrowly from day to day by 600 to 900 mL (<1% body mass). One measure of fluid intake adequacy involves enough fluid to prevent meaningful body water deficits outside this euhydration range (i.e., dehydration). A second measure of fluid intake adequacy involves enough fluid to balance the renal solute load, which can vary widely inside the euhydration range. The subtle but important distinction between the two types of adequacy may explain some of the ambiguity surrounding the efficacy of hydration status markers.
The results show that adequate fluid intake can be dually defined as a volume of fluid (from water, beverages, and food) sufficient to replace water losses and provide for solute excretion. Fluid needs can differ greatly among individuals due to variation in the factors that influence both water loss and solute balance; thus, adequacy is consistent with a wide range of fluid intakes and is better gauged using hydration assessment methods. Adequacy of fluid intake for replacing meaningful water losses (dehydration) can be assessed simply, inexpensively, and with reasonable fidelity among healthy, active, low-risk individuals. Adequacy of fluid intake for solute excretion per se can also be assessed among individuals but is more difficult to define and less practical to measure.
The purpose of this article is to explain the theory and practice for using common hydration assessment methods to distinguish between fluid intake adequacy for replacing water losses and balancing solute load. To the authors' knowledge, no paper has addressed fluid intake adequacy using hydration assessment or approached the question with dual perspectives on adequacy. When combined, this approach should improve our application of hydration assessment measures for determining fluid intake adequacy.