Beware!  They're adding things to your food to make you fat!  —  It's what clients are constantly telling me when we discuss their fear of eating at restaurants or the guilt they feel after. 

I jokingly call it the "conspiracy theory" to help them find humor in it.  People often suspect that restaurants are adding all sorts of things secretly to their food that makes it so high in calories that their body will be forced to store it all as fat. 

Let's think logically for a minute:

A restaurant's job is to make food that people want to buy.  They are a business, and they won't stay in business if people don't buy their product.  So they make food that tastes good because this is the #1 factor in what most people choose to eat.  Sure, to make the food taste good they season it with spices, salt, sauce, butter/oil, and other flavor-enhancing ingredients.  But this doesn't mean it's going to make you fat. 

Remember, we store energy as body fat when we consume more energy than what our body needed.  This extra energy (i.e. calories) could have come from any food, regardless of whether it's from a restaurant or not.  It could have come from raw broccoli if you ate enough of it (which it would be hard to do, but you get my point). 

Despite what Michael Spurlock would tell you (the guy in the documentary Supersize Me) it is possible to eat at restaurants without gaining weight.  If you eat when you're hungry, the foods your body wants and stop when you are satisfied your body will internally regulate for your weight to stay stable. 

The conspiracy theory is just that, a silly theory that is based on myths we tell ourselves.  The truth is that you can eat any food you want and not gain weight, as long as you are doing it in a way that honors your body's signals.