Effects of Sodium Reduction on Energy, Metabolism, Weight, Thirst, and Urine Volume

Two recent studies challenged traditional paradigms of mammalian sodium physiology, suggesting that sodium reduction might cause weight gain by altering metabolism. This new theory has important implications for population-wide dietary recommendations. However, these observations have not been confirmed. In the DASH (Dietary Approaches to Stop Hypertension)-Sodium trial, 412 adults with systolic blood pressure of 120 to 159 mm Hg and diastolic blood pressure of 80 to 95 mm Hg not taking antihypertensive medications were randomly assigned to the DASH diet or a control diet (parallel design). On their assigned diet, participants randomly consumed each of the 3 sodium levels for 4 weeks (crossover design). Participants were provided all meals but could drink noncaloric beverages (eg, water) freely. Throughout the trial, energy intake was adjusted to maintain weight constant. The 3 sodium levels (at 2100 kcal/day) were: low (1150 mg of Na/day), medium (2300 mg of Na/day), and high (3450 mg of Na/day). Energy intake, weight, self-reported thirst, and 24-hour urine volume were assessed after each period. Participants were 57% women and 57% black; mean age was 48 years [SD, 10]). Among those assigned the control, mean weight increased slightly with higher sodium but not among those assigned DASH. Energy intake did not vary across sodium levels in either diet ( P -trends ≥0.36). Higher sodium resulted in more thirst ( P -trends <0.001 on both diets) and higher urine volume (suggesting higher fluid intake) during the control diet ( P -trend=0.007). Reducing sodium did not increase energy requirements to maintain stable weights but did decrease thirst and urine volume (control diet only), findings consistent with the traditional understanding of mammalian sodium physiology. Clinical Trial Registration URL: http://www.clinicaltrials.gov . Unique identifier: NCT00000608.