It's a theory that's based on common sense, which is a bad scientific method, but which comes up with a counter-intuitive conclusion, which, equally superficially, makes me think it must be right. But here goes, and if you are a nutritionist let me know what you think.
I would think it's likely that when the body detects sweetness, it expects that a load of calorie-full carbohydrates is coming its way. And so it would make adjustments to prepare for that. This is where some knowledge would help, but let's just say that for example the sugar level of the blood is reduced by storing that sugar somewhere. I need to generalise this even further. Expecting more energy, the body stores its existing free energy in an energy store, a notional organ I'll call the battery. When the energy doesn't arrive, the body reclaims energy from the battery. Normally, energy is only drawn from the battery when it is needed, in response to exercise, perhaps. So now the body is acting as if it is expanding energy, when it isn't. And this causes a sense of lack: hunger. Which you don't get with real sugar (although, admittedly, it rots your teeth).
I've found some academic support for this theory. At the end of this news release from Bristol University we find this:
Although not covered by this particular experiment Dr Hans-Peter Kubis also explains how low or zero calorie drinks with artificial sweeteners do not necessarily provide the answer either. As people drink these, our subconscious expects a sugar and calorie laden treat, but on not ingesting these calories, people are more likely to over eat at the next opportunity to make up for the calories people were expecting to consume in the low-cal drink. This is not proven in humans, in fact there is a good argument for funding far more research in this area.He attributes the effect to the subconscious, rather than physiology, but it seems there hasn't been much research. He's right to say there's a good argument for more research, and I wish I was in a position to do it. The answer in the meantime, of course, is to adjust your palate to need less sweetness, real or fake. Drink water.