You should understand that the zero fat on the label is a rounding off game played by the food manufacturers. If the number of calories measured in the spray is less than a certain amount, the government allows you to round the number down to zero. Do you actually limit your spray to the 1/3 of a second the nutrition label calls for?
The spray oil has the same 120 calories per tablespoon as the olive oil. the difference is, in a 1/3 of a second spray, you don't get a lot of oil.
Besides, you really don't have to use anywhere near a tablespoon of oil to lightly coat garlic or onion before roasting.
Good luck with your diet.
"If you want to make an apple pie from scratch, you must first create the universe." -Carl Sagan