You raise an interesting question. I did some research to find out about these products and what they actually contain. While the nutritional labels do state that they contain zero fat and zero calories, something more than just air comes out when you spray. A little checking produced some illuminating information about how manufacturers and marketers can legally claim that products have no fat or calories, when the opposite is true.
The FDA permits foods to be labeled "fat-free" if they contain less than 0.5 grams of fat per serving. The labels of some products I checked said that a single serving is one spray providing 0.2 grams (2 tenths of a gram) of the product for cooking and five sprays when you're using it as a topping. I found calculations showing that to get a single 0.2 gram serving you would have to spritz for about one-third of a second, something that is almost impossible to time. If you spritz for five seconds, you'll be adding as many as 35 calories of fat to your food.
Looking at the ingredients list, I saw that one product contains water, soybean oil, buttermilk, salt, soy lecithin and polyglycerol, esters of fatty acids (emulsifiers), xanthan gum, potassium sorbate and sodium benzoate (to preserve freshness) lactic acid (acidulant), artificial flavor, and beta-carotene for color.
Refined soybean oil, the second ingredient on the list, is a cheap vegetable oil that we should all avoid¸ because it is responsible for the excess of pro-inflammatory omega-6 fatty acids in the mainstream diet.
In any case, recent research indicates that an extreme emphasis on low-fat foods in pursuit of cardiovascular health may be misplaced; it appears that sugar and flour are bigger culprits. My preference would be to use a small amount of olive oil for flavoring - you can put it in a pump bottle to cut down on the amount you use; for cooking, you can use a pastry brush to add it to a pan. As for popcorn, I like it sprinkled with a little tamari, some nutritional yeast, garlic powder and, sometimes, cayenne pepper. Or try it with chili powder, a little grated Parmesan cheese or dried dill. If you don't use oil, mist the popcorn lightly with a little purified water before adding dry flavorings to help them stick.
Andrew Weil, M.D.