The term “fast food” is in common use and has also been used in research studies. It doesn’t simply mean food that is quick to prepare, because the speed of preparation of a food has nothing to do with how healthy it is. It generally refers to readily available, highly processed convenience foods that tend to be high in calories (from fat or sugar) and salt, and low in dietary fibre, and that are often consumed frequently and in large portions.

Most of the evidence linking fast foods to weight gain refers to foods such as burgers, fried chicken pieces, French fries (chips), and fatty drinks (e.g. smoothies or milkshakes) or sugary drinks, as served in international franchised outlets, and they have this effect because they are high in calories and have high calorie content for small portion (energy dense foods).