Fear, Gastrointestinal Distress, and Interoception: Physiological and Psychological Mechanisms in Eating Disorders

Primary outcomes

1. Subjective Rating of Fear

   Time frame: -10 minutes, 0 minutes (immediately after the intervention), and 10 minutes post-intervention

   Area under the curve with respect to increase (AUCi) from the 10 minutes period prior to the meal until immediately after the meal will be used to characterize changes in Visual Analogue Scale ratings of momentary fear ranging from "Not at All (0)" to "Extreme (100)." AUCi was calculated as: (((Fear at -10 minutes)+ (Fear at 0 minutes))*10/2) + (((Fear at 0 Minutes)+(Fear at +10 minutes))*10/2) - (Fear at -10 minutes)*20. A more positive score indicates greater increases in fear over the pre to post meal period.

2. Difference in Average Skin Conductance

   Time frame: -10 minutes, 0 minutes (immediately after the intervention), and 10 minutes post-intervention

   Skin conductance data will be collected in microsiemens using a Biopac Bionomadix EDA System during the period before and after the test meal. The difference in average microsiemens will be computed for each test meal using the following equation: (Average activity for the 10 minute meal period) - (average activity for the 10 minutes prior to the meal). A higher difference indicates increased physiological activation during the meal period relative to the pre-meal period.

3. Gastrointestinal Distress

   Time frame: -10 minutes, 0 minutes (immediately after the intervention), and 10 minutes post-intervention

   Gastrointestinal distress will be the averaged visual analogue scale ratings of "Nausea" and "Stomach Ache" ranging from "Not At All (0)" to "Extreme (100)." Area under the curve with respect to increase (AUCi) from the 10 minutes period prior to the meal until immediately after the meal will be used to characterize changes gastrointestinal distress. AUCi was calculated as: (((Gastrointestinal distress at -10 minutes)+ (Gastrointestinal distress at 0 minutes))*10/2) + (((Gastrointestinal distress at 0 Minutes)+(Gastrointestinal distress at +10 minutes))*10/2) - (Gastrointestinal distress at -10 minutes)*20. A more positive score indicates greater increases in gastrointestinal distress over the pre to post meal period.

4. Cholecystokinin Response

   Time frame: 0 minutes (immediately after the intervention), 10 minutes, 20 minutes, 30 minutes, 60 minutes and 90 minutes post-intervention

   Blood was drawn repeatedly. Cholecystokinin (CCK) values in plasma were quantified in ng/mL using a commercially available enzyme immunoassay (Phoenix Pharmaceuticals EK-069-02). Area under the curve with respect to increase (AUCi) was calculated from the time period immediately before the test meal to 90 minutes after the test meal. AUCi was calculated as: (((CCK at 0 Minutes)+( CCK at +10 minutes))*10/2) + (((CCK at 10 Minutes)+( CCK at +20 minutes))*10/2) + (((CCK at 20 Minutes)+( CCK at +30 minutes))*10/2) + (((CCK at 30 Minutes)+( CCK at +60 minutes))*30/2) + (((CCK at+ 60 Minutes)+( CCK at +90 minutes))*30/2) - (CCK at -10 minutes)*90. A more positive score indicates greater increases in CCK over the pre to post meal period.

5. Peptide YY Response

   Time frame: 0 minutes (immediately after the intervention), 10 minutes, 20 minutes, 30 minutes, 60 minutes and 90 minutes post-intervention

   Blood was drawn repeatedly. Peptide YY (PYY) values in plasma were quantified in ng/mL using a commercially available enzyme immunoassay (Phoenix Pharmaceuticals EK-059-02). Area under the curve with respect to increase (AUCi) was calculated from the time period immediately before the test meal to 90 minutes after the test meal. AUCi was calculated as: (((PYY at 0 Minutes)+( PYY at +10 minutes))*10/2) + (((PYY at 10 Minutes)+(PYY at +20 minutes))*10/2) + (((PYY at 20 Minutes)+( PYY at +30 minutes))*10/2) + (((PYY at 30 Minutes)+( PYY at +60 minutes))*30/2) + (((PYY at+ 60 Minutes)+( PYY at +90 minutes))*30/2) - (PYY at -10 minutes)*90. A more positive score indicates greater increases in PYY over the pre to post meal period.

6. Subjective Rating of Fullness

   Time frame: 0 minutes (immediately after the intervention), 10 minutes, 20 minutes, 30 minutes, 60 minutes and 90 minutes post-intervention

   Fullness will be the averaged visual analogue scale ratings of "full" and "satiated(satisfied)" ranging from "Not At All (0)" to "Extreme (100)." Area under the curve with respect to increase (AUCi) will be used to characterize changes in fullness from immediately before the test meal to 90 minutes after. AUCi was calculated as: (((Fullness at -10 minutes)+ (Fullness at 0 minutes))*10/2) + (((Fullness at 0 Minutes)+( Fullness at +10 minutes))*10/2) + (((Fullness at 10 Minutes)+( Fullness at +20 minutes))*10/2) + (((Fullness at 20 Minutes)+( Fullness at +30 minutes))*10/2) + (((Fullness at 30 Minutes)+( Fullness at +60 minutes))*30/2) + (((Fullness at 60 Minutes)+( Fullness at +90 minutes))*30/2) - (Fullness at -10 minutes)*100. A more positive score indicates greater increases in fullness over the pre to post meal period.

7. Urges to Restrict Food Intake

   Time frame: 60 minutes post-intervention

   Visual analogue scales will assess momentary "urge to restrict" from "Not At All" (0) to "Extreme" (100). The 60 minute assessment will be used for the exploratory serial mediation model.