A study has been released showing the same hypothesized effects of fake fat that have been speculated to exist for fake sugars. Namely, our bodies taste fat and sugar, and thus prepare for an influx of calories. When no influx comes, it throws our metabolisms out of whack, our energy levels drop, and our bodies amp up the drive for more food.
Christopher Wanjek has a good article on it over at Live Science, but there are a few things that I want to add. Primarily, even if we didn't suffer negative effects from fake fats and sugars, they would still be a bad thing.
The emotional awakening that is required to not only start a healthy life, but stick with it, requires abandoning old eating habits and behavioral patterns. When I ditched pre-packaged food and soda years ago (and lost nearly fifty pounds in the process) I went back some time later and tried to eat the foods that once constituted so much of diet and I couldn't! Doritos tasted like cheese-flavored slime, Snickers burned going down, Coca-Cola caused a near-instantaneous diabetic coma; this food tasted like shit!
It was my emotional, physiological epiphany. So much of the food that we start eating as kids remains tasty simply because we keep eating it. If we break the pattern of sugary consumption that started when young, we lose our taste for the foods.
Fake sugars and fats does not do this. We try to maintain our old, unhealthy patterns with fake food and are surprised when our diets fail?! Of course they fail! The behavioral patterns that foster poor eating are only encouraged with fake junk food. We need to eliminate the sensation of junk food altogether. We need to replace it with healthy foods until we stop craving the junk. Then, the emotional and cognitive changes necessary to lead a healthy life have taken place.
Admittedly, for some people, this is easier said that done. The only junk food that I crave anymore is ice cream and the occasional root beer float, but for others, the cravings may persist. But no matter how strong your desires, the only way to win is to eliminate the cravings. If your dietary life is defined by resisting temptation, you've already lost. You have to find a way to eliminate the temptation, or reduce it to a point where it rarely enters your mind. Using fake fats and sweets does not encourage behavioral changes and only serves to make you weak in the face of junk.