The Effect of Hydration Status on Glycemic Control and Appetite Regulation
Condition: Healthy
Study type: Interventional

Summary: 
      The aim of this study is to investigate whether hydration status affects blood sugar control
      and appetite regulation. In order to do this, participants will undergo a monitoring phase
      whereby their weight, diet and physical activity are monitored, followed by a dehydration
      protocol involving fluid restriction and sitting in a heat tent. In one arm of the trial,
      participants will remain dehydrated for the remainder of the day (i.e. after the heat tent)
      by having their fluid intake restricted, and in the other arm of the trial, participants will
      be rehydrated by consuming the necessary amount of plain water. All participants will undergo
      both arms of the trial, the order of which will be chosen randomly.

      Several measures will be taken throughout the trial. Before participants go into the heat
      tent, they will provide a urine sample (for baseline hydration status as indicated by urine
      osmolality), a blood sample (for glucose, insulin, arginine vasopressin,/copeptin, ghrelin
      and serum osmolality and plasma volume), and have a peripheral quantitative computer
      tomography scan of their thigh to indicate muscle size. On the day proceeding the heat tent,
      participants will have these measures repeated, along with metabolic rate before consuming a
      75 g glucose drink, followed by 15 minutely blood samples and hourly metabolic rate measures
      for 120 minutes (i.e. an oral glucose tolerance test; OGTT). Following this, participants
      will be presented with a large bowl of pasta and sauce and will be instructed to eat until
      satisfied (maximum 30 min). Blood samples will be taken every 10 minutes for 60 minutes
      following the meal.

      Participants also have the option to opt-in to have a muscle biopsy taken. This will be taken
      before and ~120 minutes after the glucose drink.
    

Detailed description: 
      The aim of this study is to investigate whether hydration status affects blood sugar control
      and appetite regulation. This will be a randomised crossover trial with two trial arms
      separated by 5-35 days. Each trial arm consists of five days in total, with the only
      difference between the trial arms being the amount of fluid consumed after the heat tent on
      day 4 (as described below).

      Days 1-3 of each trial arm are the monitoring phase. Participants will be given a chest
      mounted activity monitor (ActiHeart TM), some body mass scales, a food diary with food
      weighing scales and three urine sample pots. Participants will be required to provide a urine
      sample upon waking, and note their weight before eating. The activity monitor will need to be
      worn from midnight on day 1 in order to gauge three full 24-h periods of activity. The food
      diary will also start at this point; participants will be required to weigh and record all
      their food and beverages (including recording the leftovers). On day 3 of the monitoring
      phase, participants will be required to continue their normal daily routine, however they
      will be provided with a set amount of water to consume (40 mL/kg lean body mass) in order to
      standardize baseline hydration status. No food or fluid will be allowed to be consumed after
      2200 h on day 3.

      On day 4, participants will take the same measures (weight and urine sample) and will arrive
      at the university in a fasted state (i.e. no food or fluid). A blood sample will be drawn
      from an antecubital vein followed by a peripheral quantitative computer tomography (pQCT)
      scan of the thigh. After the blood sample and scan, participants may eat food from a list of
      low water-content foods only for the rest of the day. At approximately midday (flexible
      depending on the participants' availability, but matched on both trial arms), participants
      will be weighed again, and placed in a heat tent (40-50 degrees Celsius) until they lose 1 %
      of their pre-heat tent weight or for a maximum of one hour (whichever comes first). On the
      second trial arm, participants will be matched by percentage of body mass loss, even if this
      requires spending more or less time in the heat tent, but still no more than one hour.

      After the heat tent, participants will receive a salty meal in order to facilitate fluid
      absorption/retention. This will be matched in both trial arms in order to reduce confounding.
      In the dehydration trial arm, participants will be provided with 3 mL/kg lean body mass of
      plain water to consume for the rest of the day. In the rehydration trial arm, participants
      will be given 40 mL/kg lean body mass plus 150 % of their body mass losses from the heat
      tent. This will be metered out throughout the day to maximise rehydration. Thus the amount of
      water consumed on day 4 after the heat tent is the only discernible difference between the
      trial arms, with everything else matched. In both trial arms only plain water (i.e. no
      caffeine or alcohol) will be allowed to be consumed, and only foods from the dry food list
      can be eaten. This will be matched on the subsequent trial arm. No food or fluid after 2200 h
      on day 4.

      On the fifth day of each trial arm, participants will be required to attend the laboratory at
      approximately 0730 h (± 1 h). A urine sample will be collected, along with body mass. Another
      pQCT scan of the thigh will be taken and participants' metabolic rate will be measured using
      the Douglas bag method. As part of the trial, participants are able to opt-in for a muscle
      biopsy. If they have opted-in, a muscle biopsy will be taken after the pQCT scan. This will
      involve a local anesthetic (Lidocaine), making a small incision using a scalpel, then
      obtaining a muscle sample using the Bergstrom technique. Participants will then be fitted
      with a cannula, and their hand will be placed in a 60 degree Celsius hotbox for five minutes,
      after which a baseline blood sample will be drawn. Participants will be given a 75 g glucose
      drink to consume within five minutes. Whilst remaining rested, a researcher will draw a 10 mL
      blood sample every 15 minutes for 120 minutes, with approximately 10 mL saline infused after
      each blood sample drawn. Metabolic rate will be measured at 0 (pre-OGTT), 60 and 120 minutes.
      For the participants who opted-in for the muscle biopsy, another one will be taken after 120
      minutes.

      Participants will then be presented with some computer based appetite assessing psychological
      inventories to assess subconscious food preferences. These tests are pilot data for future
      research. Following this, participants will be presented with a pasta meal, with the
      instruction to eat until satisfied for a maximum of 30 minutes. After 30 minutes, a blood
      sample will be drawn, followed by 10 minutely samples for 60 minutes. Visual analogue scales
      for subjective appetite ratings will be taken pre-meal, immediately, post-meal, then at 30
      and 60 minutes post-meal. The cannula will then be removed.

      The sample size required for this trial is 16 participants, calculated using pilot data which
      assessed blood glucose control after being dehydrated and rehydrated. Based on that pilot
      study, hydration status resulted in a marked difference in the rate of return to fasted
      glycaemia. This primary conclusion was supported by a magnitude of effect 45 minutes
      post-oral glucose tolerance test (D = 1.1 mmol/l). The standard deviation at this time point
      in the control (normal hydration) group was also 1.1 mmol/l, resulting in an effect size (d)
      of ≈1. To provide a 95 % power (beta level) to detect this effect at an alpha level (p) of
      less than or equal to 0.05 using a 2--tailed paired t--test will require ~16 participants.

      If any participant does not complete the study (i.e. they have missing data), their data will
      not be included in the analysis. In other words, the analysis plan will be per protocol
      (completers only). The statistical techniques used will be linear modelling with post-hoc
      t-tests corrected for multiple comparisons where relevant. However, until the final dataset
      has been obtained, the statistical tests may be subject to change (e.g. if data are
      non-parametric).
    

Intervention name(s): Hypohydrated; Rehydrated
Intervention type(s): Behavioral; Behavioral
Intervention description(s): Participants remain hypohydrated after the heat tent procedure; Participants rehydrate after the heat tent procedure
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: Hydration; Glycemic control; Appetite; Endocrinology