More on the relationship between obesity, delicious food, and the magic of gastric bypass.
Roux-en-Y gastric bypass surgery changes food reward in rats (Shin et al., 2011 Intl Journal of Obesity)
I wish I knew how, but this study definitely shares a theme with the remarkable effects of a bland diet and spontaneously reduced caloric intake in obese but not lean subjects, (from the first post in this series, found here).
In brief, there were 3 groups of rats in this study: 1) diet-induced obese (“sham”); 2) diet-induced obese rats that underwent gastric bypass surgery (“RYGB”); 3) chow-fed lean controls (“lean”). The dietary regimen was a kerfuffle, but that wasn’t really the point of the study; to make the rats obese, they were given standard chow, a purified high sugar high fat diet, and chocolate-flavoured Ensure all at once… and we have no idea how much of each they were consuming :/ But here’s the nutrient breakdown of each anyway, by calories: 
and here is a rough ingredient list:
HFD, high fat high sugar diet
They performed a battery of psychological evaluations designed to empirically measure how much an animal “wants” or “likes” a rewarding food. Call me simple, but I would’ve rather just seen how much of each of the above diets the rats consumed when presented with all 3 simultaneously. If most of their calories came from the sweet chocolate-flavored Ensure, then I’d say they still liked rewarding foods. If on the other hand they selected more of the sugar-free chow, then they probably don’t care as much for rewarding food. Maybe this wouldn’t fly in psychonutrition circles, but I don’t really think such circles exist. Alternatively, would RYGB rats have lost more weight if they were fed exclusively chow compared to those given Ensure? Fortunately, this question was addressed in an earlier manuscript by Zheng (Meal patterns, satiety, and food choice in a rat model of Roux-en-Y gastric bypass surgery [Zheng, Berthoud, et al., 2009 AJP])
When given the sugar-free chow diet, the control rats eat less. When given a high sugar high fat diet, the control rats eat more. RYGB rats don’t seem to care. But that’s kind of exactly what Shin showed by complicated psychological tests:
Lean and sham (obese) rats like a very sweet beverage (1.0 M sucrose) significantly more than a more bland solution (0.01 M sucrose). RYGB rats don’t seem to care. This was repeated to a tee in another group of “obesity-prone” rats suggesting it might be a true product of the gastric bypass surgery:
And oddly enough, human subjects that have undergone roux-en-Y gastric bypass surgery seem to be able to detect much lower concentrations of sucrose but not like it as much (they can “taste” it more, but might not “like” it more) (they are satisfied with less-sweet foods) (Changes in patients’ taste acuity after Roux-en-Y gastric bypass for clinically severe obesity [Burge et al., 1995 JADA])
Are these findings related to obese humans who spontaneously consume significantly less of a bland diet? (recall obese but not lean human subjects lost weight on the bland diet). Similarly, rats consume significantly more of a tasty junk-food cafeteria diet. There is definitely something magical about roux-en-Y gastric bypass surgery; it is the single most effective treatment [cure] for obesity. Obese humans eat less of a bland diet, roux-en-Y gastric bypass surgery decreases the “liking” of a sugar-rich beverage (but enhances one’s ability to detect sucrose)… RYGB and that bland diet caused massive weight loss in their respective [obese] subjects… These things just have to be related, my spidey-sense is going wild
calories proper