Definition [edit]. The Macmillan Dictionary defines 'superfood' as a food that is considered to be very good for your health and that may even help some medical conditions.The Oxford Dictionary definition states a superfood is “a nutrient-rich food considered to be especially beneficial for health and well-being”.The group Cancer Research UK says, the term 'superfood' is really just a marketing tool, with little scientific basis to it.pecifically, blueberries, as a popular superfood example, are not especially nutrient-dense (considered to be a superfood characteristic), having moderate content of only three essential nutrients: vitamin C, vitamin K and manganese.