High-energy food is food that supplies a large number of calories per bite — fats, oils, sugars, confectionery, fried foods, and fatty meats — giving the body abundant fuel when digested. Energy density is the key measure: fat’s 9 kcal per gram makes oily and fatty foods the most concentrated sources, while water- and fibre-rich foods like vegetables are dilute. High-energy foods are valuable where energy needs are extreme — endurance athletes, manual labourers, famine relief, and catch-up growth in malnourished children (therapeutic pastes like Plumpy’Nut are engineered for maximum energy density). For sedentary modern life, though, their effortless calories are a principal driver of overweight — satisfying to eat, easy to overeat.