4 The Effect of Hydration Status on Glycaemic Control and Appetite Regulation

Background: Cell volume and arginine vasopressin are implicated in glycaemic control and are influenced by hydration status [1, 2]. During hypohydration, a deterioration in glycaemic control has been demonstrated in type 1 [3] and type 2 diabetic patients [4]. Our pilot data replicated such findings in healthy adults [5]. Little is known about whether hydration status per se alters appetite. Objective: We therefore aimed to assess whether glycaemia and appetite are affected by hydration status in healthy adults. Methods: In this randomised crossover trial, healthy participants (8 men, 8 women) underwent an oral glucose tolerance test (OGTT) and multiple appetite tasks in a hypohydrated and euhydrated state. After successfully matching lifestyle factors three days pre-trial, participants had a fasted pre-trial blood sample, followed by dehydration in a 45 [+ or -] 1.5[degrees]C heat tent for 1-hour followed by fluid restriction (HYPO) or replacement (RE). The following day, an OGTT was conducted with regular blood samples and metabolic rate measures for 120 min. Subsequently, a desire-to-consume task was completed followed by an ad libitum pasta-meal with a pre-prandial and multiple postprandial visual analogue scales and blood samples for 60 min. Peripheral quantitative computer tomography (pQCT) thigh scans were taken pre-trial and on the trial-day to assess changes in muscle area as a proxy for cell volume. Analysis involved repeated measures ANOVA for trial and time trends during the OGTT and meal test, t-tests comparing pre-trial and trial-day values, and linear regression to assess desire-to-consume according to nutrien-tcontent of foods. Results: HYPO was confirmed by increases in urine osmolality and specific gravity and 1.8 [+ or -] 1.2% body mass loss, which did not occur during RE (0.1 [+ or -] 0.6% body mass loss). Further, during HYPO, muscle area decreased by 2.9 [+ or -] 2.4% (p = 0.007) compared to pre-trial, with accompanying increases in serum osmolality (pre-trial 287 [+ or -] 5 mOsm/kg, trial-day 296 [+ or -] 5 mOsm/kg; p < 0.001), and plasma copeptin (pre-trial 4.45 [+ or -] 2.01 pmol/L, trial-day 18.85 [+ or -] 9.92 pmol/L; p < 0.001), both of which remained elevated throughout the OGTT (trial p [less than or equal to] 0.002). During the OGTT, hydration status did not meaningfully alter the serum glucose or insulin response, including no differences in the area under the curve (p [greater than or equal to] 0.469) or time-to-peak (p [gr