They all work together to keep you healthy and functioning. When there is an overabundance of copper, for example, it will result in lower levels of zinc. So whether you are trying to gain, lose, or maintain weight, stick to eating a balanced diet and a variety of different foods, and avoid any advice that tells you different. At the most basic level, your body accumulates fat when you eat more than you need, and it loses fat when you use more energy than you have ingested in your food. When energy in equals energy out, there is no change in weight.
Individuals differ considerably in how efficiently they digest food.
They also differ in how active they are, and in how many calories they burn up through exercise. But we can generalize and say that one pound of fat contains about 3,500 calories for more people. We can eat less. We can exercise more. Ideally, to lose weight and stay healthy you should do both.