While most of us think that fats in foods make us fat, the truth is: too much of any macronutrients that results to higher calories for the day, is what makes us really fat.
I read somewhere that low or non fat foods are usually filled with sugar to make up for the flavor that was taken out.
For example: Low Fat Skippy Peanut Butter
Peanut Butter is supposed to be loaded with healthy, monounsaturated fats which should be good for us since they provide a number of the fat soluble vitamins and minerals required by our body. Well, the manufacturers take them out so they can say it has low fat. And then, they add a lot of sugar to make up for the flavor, which adds more calories than the 'normal fatty' Skippy Peanut Butter. Sugar can make you fat because it causes insulin release when glycogen stores are already filled, thus, it is stored as fat.
I actually went down to check my non-fat yogurt and was surprised to see that it was actually filled with sugar! It has 33 g of sugar and 0 fats!