I do not think it is placebo for me for two reasons. First, I went into the "experiment" fully NOT expecting it to work because two years ago, I had incorrectly tried it before I fully understood the approach. At that time, I had read a summary of Seth's paper, and (incorrectly) tried sugar water with or near my meals. I WANTED it to work then, too, but it did not -- at all. Obviously, no placebo effect and no "wanting" effect in that case. Secondly, I might buy either of those as potential explanations if the effect had lasted a couple of weeks or maybe a month. I've been doing this for almost 8 months now. I have consistently, almost without exception, been able to easily maintain a calorie consumption level of around 1,800/day, whereas my maintenance level is at about 2,200 calories, and before I started the SLD, I was routinely eating between 2,500 and 3,000 per day. I think the normal setpoint mechanism is so powerful that it is hard to imagine the placebo or the want-to effect having that much of an effect for that long.
Again, I come back to my original comment, that there is almost nothing that works for everyone all the time -- including drugs such as anti-depressants, anti-biotics, etc. The fact that it IS working for me does not prove that it is a large-scale viable approach (although my guess based on my reading of many others' experiences is that it quite likely is), nor does the fact that it is not working for you mean that it isn't (or that it is snake-oil).