During the recent PBS special on obesity Fat: What No One is Telling You, a segment about surgery included this voiceover:

Until recently it was believed that the tiny stomach [that the surgery produces] is what forces the patient to eat less and lose weight. The surprise came when researchers learned that what makes surgery work so well is the cutting of some nerves in the bowel, which changes signals which flow between the gut and the brain.

I’m not surprised the researchers were surprised. The obvious function of nerves from gut to brain is to tell the brain food is present in the gut; and when enough food is present, to cause satiety. If this view of what the nerves do is correct, you would think that cutting those nerves reduces satiety signals and thus increases how much people eat at each meal — and thus causes weight gain. But the opposite is what happened.

The theory behind the Shangri-La Diet, however, easily explains the weight loss: Cutting the nerves reduced the calorie signal from food, thus reduced the strength of the flavor-calorie association. (After nerves are cut, your brain thinks that a 300-calorie food only has 150 calories. So the flavor-calorie association becomes weaker.) The weaker the flavor-calorie associations of your food, the lower your set point. The observation supports the theory so well that I will try to track it down to include in a revision of my paper.

The implication is that weight-loss surgery could consist of cutting some of those calorie-signalling nerves and nothing more. It would be relatively painless: Food would still taste good, especially in the beginning. (Because cutting the nerves does not change the memory stored in the brain.) Food would gradually taste less good as the flavor-calorie association become weaker. As flavor-calorie associations become weaker, your set point goes down. Causing weight loss without effort.