A diet causes you to gain, lose, or maintain weight. It depends on how many calories you eat. Foods come in unique properties that include nutrients, calories, and portion sizes. The best diet you can choose is one that meets your nutritional and energy needs. By eating healthy foods and leading an active lifestyle, you give yourself the best chance to reach your fitness goals.
When you want to lose weight, you must eat a calorie deficit. You can achieve this by eating fewer calories than you use each day. When you want to gain weight, you must eat a calorie surplus. Gaining weight is different from gaining muscles. Protein is the only nutrient that can build muscle. Thus, if you are looking to build muscle, you must eat a calorie deficit and protein.