Read the label of the product, there are usefull informations on them.  The ingredians are listed on descending order. For example the fat content in milk coud be 3.6, 2.8, 1.5, 0.1 %. it is easier to choose this way.  Is there any sugar (carbohydrate) in the product? The one which usually contains sugar, but it is replaced by sweetener called: "light". For exammple fruit juces, sodas, marmelades etc...). Not to be mistaken with the sign "diabetic", because in those products the energy content could be high, only it can be eaten by a diabetic person!   Don't overshop yourself, eat something before shopping. Don't go shopping with empty stomac!  Don't eat the leftovers or the product just becasue it would be expired.