Gastric bypass surgery (GB) is a safe, effective treatment for morbid obesity(1). Aside from reduced energy consumption, patients report changes in food preferences and appetite that may contribute to weight loss post-surgery(2,3). Food preferences can be separated into two constructs; ‘liking’ (pleasure) and ‘wanting’ (motivation/desire to eat)(4) which may be influenced by physiological and psychological changes post-surgery. The aim of this study was to investigate changes in food preferences (‘liking’ and ‘wanting’) in GB patients from pre- to post-surgery, compared to weight-stable controls. 
     Nineteen patients (45.2±12.5 years, Body Mass Index (BMI): 45.3±6.4kg/m2) and sixteen time-matched controls (44.7±15.6 years, BMI: 25±4.4kg/m2) completed the computer-based Leeds Food Preference Questionnaire, which assesses preferences for sweet/savoury foods and low-fat/high-fat foods(5), at baseline (1-month pre-surgery) and 3-months post-surgery. Explicit liking and wanting (conscious hedonic feelings/desire to consume) were measured using Visual Analogue Scales, whilst implicit wanting (unconscious motivational expression) was measured using food selection and reaction times in a forced-choice task. 
     There were no significant differences in food preferences between patients and controls at baseline. BMI for controls remained stable (+0.1±1.3kg/m2, p=0.73), whilst BMI in patients significantly decreased (-8.3±2.7kg/m2, p=<0.01). GB patients expressed a significant decrease in the explicit liking (F(1,33)=10.42, p=0.03), explicit wanting (F(1,33)=5.76, p=0.02) and implicit wanting (F(1,33)=4.92, p=0.03) for sweet foods after surgery. However, there were no significant changes in preferences for high-fat foods in patients from pre to post-surgery. There were no significant changes in preferences for controls for sweet or high-fat foods. 
     In conclusion, patients express a significant decrease in preferences for sweet foods post-surgery. As changes in implicit unconscious motivational expression of food preferences may be more predictive of actual food consumption(6) these findings highlight a possible mechanism responsible for the success of GB as an obesity treatment. 
	
1. Colquitt JL, Pickett K et al. (2014) Cochrane Database Syst Rev 8, CD003641.	 
2. Mathes CM & Spector AC (2012) Physiol Behav 107, 476-483.
3. Miras AD & Le Roux CW (2013) Nat Rev Gastroenterol Hepatol 10, 575-584. 
4. Berridge KC & Robinson TE (2003) Trends Neurosci 26, 507-513.
5. Finlayson G, King N & Blundell J (2008) Appetite 50, 120-127. 
6. Pool E, Sennwald V et al. (2016) Neurosci Biobehav Rev 63, 124-142.

09. Changes in implicit wanting and explicit liking and wanting for food after gastric bypass surgery.