One of the first lessons I learned in intuitive eating was that substitutions are unsatisfying. That is, if what I really, really want to eat is a baked potato with butter on it, then a baked potato with margarine or olive oil probably isn't going to cut it. Neither is a pretzel. Or an eclair. Or air-popped popcorn. When you're tuned in to your appetite, you can't pretend you want something else.
That holds true whether what you want is a hot fudge sundae or a bowl of kale with sesame seeds, both of which I find delicious at various times. And if you give me the sundae when I want the kale, I'm probably going to keep on eating until I'm either overly full or I find a bowlful of kale.
Now a new study done by Susan Swithers and Terry Davidson at Purdue University now supports the notion that certain kinds of substitutions just make you eat more. (Scroll down the link page for a free PDF of the study.) They found that rats given yogurt sweetened with saccharin ate more, gained more weight, and developed more body fat than rats who ate yogurt with sugar.
In other words, you can trick your mind, but you can't trick your body. Any food is unsatisfying when it's not what you really want, and fake crap like saccharin, aspartame, etc. is especially unsatisfying. Unless what you really want is a mouthful of chemical aftertaste.
I'm sticking with sugar, myself.