Fats are a type of lipid: Organic substances that are not soluble (i.e., not able to be dissolved) in water. Dietary fats include both solids (like butter) and liquids (like cooking oils). Dietary fat is found in many common foods, including olives, avocados, nuts, seeds, meat, fish, cheese and milk.
There are three major macronutrients in your diet: fat, protein, and carbohydrates. Of these, fat is the most energy dense, meaning it contains more calories (energy) per gram. Like a super-concentrated fuel for your body, fat contains nine calories of energy per gram. This is more than twice the calories contained in a gram of either protein or carbohydrates, which each contain four calories per gram.