Effects of Diet and Exercise on Circadian Glycemia
Condition: Glucose Intolerance
MeSH terms: Glucose Intolerance
Study type: Interventional

Summary: 
      Specific aims of the study are:

        1. to evaluate whether a 24-h exposure to a 25%-carbohydrate diet will reduce postprandial
           glycemia to the same extent in the evening (19 h) as in the morning (7 h),. and

        2. to determine whether one hour of post-meal moderate intensity exercise (at 50% of
           maximal effort) will further reduce postprandial glycemia.

      The outcome measures are: plasma concentrations of glucose, insulin,
      glucose-dependent-insulinotropic peptide (GIP), leptin, and the ketone body
      beta-hydroxybutyrate.
    

Detailed description: 
      The two hypotheses in this study are:

        1. A 24-h exposure to a 25%-carbohydrate diet will reduce postprandial glycemia to the same
           extent in the evening (19 h) as in the morning (7 h), and

        2. One hour of moderate-intensity exercise (at 50% of maximal effort) will further reduce
           postprandial glycemia to the same extent in the evening (19 h) as in the morning (7 h).

      Eight postmenopausal subjects (age 58.5 years, BMI 25.6 kg/m2) participated in 4 24-h long
      crossover trials, two terminating at 7h and the other 2 at 19h. At each circadian time one
      trial required 60 minutes of moderate-intensity exercise (50% of maximal effort), and the
      other two involved no exercise.

      Three 25%-carbohydrate meals prepared by the Michigan Clinical Research Unit (MCRU) kitchen,
      were eaten at subjects' home, and the fourth was eaten 20 minutes after subjects' arrival at
      MCRU at either 19 h or 7 h. Blood was collected from antecubital catheter at 10-minute
      intervals until 23:20 h or 11:20 h, respectively.Plasma was treated with protease inhibitor
      to preserve GIP, frozen at -80o C until glucose measurements by glucose oxidase, hormone
      measurements by chemiluminescence, and ketone measurements by Abbott meter strips.

      Exercise intensity was determined before the exercise trials on a treadmill from oxygen
      consumption (VO2) and carbon dioxide production (VCO2) by subjects walking on a treadmill at
      3 mph with the treadmill slope increased by 2% every 3 minutes. Maximal effort was
      established when respiratory exchange ratio (VCO2/VO2) reached or exceeded 1. The treadmill
      speed and slope at half maximal effort was used during the one-hour exercise bout which was
      initiated 40 minutes after the start of the meal.
    

Intervention name(s): Dietary manipulation (25% carbohydrate diet) and behavioral (exercise); Dietary manipulation (25% carbohydrate diet) and behavioral (sedentary)
Intervention type(s): Combination Product; Combination Product
Intervention description(s): The 25% carbohydrate diet consisted of Pulmocare-vanilla liquid, white roll, butter, and string cheese in proportions to achieve 33% of weigh-maintenance diet containing 25% carbohydrate, 20% protein, and 55% fat. Exercise was walking 1 hour on level treadmill at 50% of maximal effort starting 40 minutes after the beginning of the meal; The 25% carbohydrate diet consisted of Pulmocare-vanilla liquid, white roll, butter, and string cheese in proportions to achieve 33% of weigh-maintenance diet containing 25% carbohydrate, 20% protein, and 55% fat. There was no exercise during this trial.
Allocation: Non-Randomized
Intervention model: Crossover Assignment
Intervention model description: The same eight subjects participated in counterbalanced order in:
(1) sedentary morning trial, (2) exercise morning trial, (3) sedentary evening trial, (4) exercise evening trial.
Masking: None (Open Label)
Primary purpose: Basic Science