Simple Substitution #3: Greek Yogurt

Both Greek and regular yogurt are fat free (or extremely close), and if you're doing it right the sugar content shouldn't be too high (as a general rule, look for less than 10 grams of sugar per serving - add dried fruit and nuts for more flavor if need be).  The biggest difference is protein content - Greek yogurt has 2X the amount of protein as regular yogurt, making it a great addition to your breakfast or a good option for a quick snack.  To save money, try the store brand Greek yogurt - I've always thought it tastes just as good as the name brand stuff.