S and SS foods are low or extra-low in energy density compared to others in the same food group so they have extra slimming power. We are advised to choose them regularly to help speed up weight loss. S is for Speedy and SS is for Superspeedy. These are entirely different to superfree however but are not mutually exclusive. So most white fish are Superspeedy for example but obviously not superfree because superfree are fruit and vegetables. However you then get some foods that are both superspeedy AND superfree. Something like melon for example.