If I were to summarize:
1. We derive energy from three major macronutrients (protein, fat and carbohydrates)
2. Our body has certain macronutrients it cannot synthesize and NEEDS for healthy functioning (essential fatty acids and essential amino acids)
3. Our bodies are largely energy efficient (by which I mean the processes to produce energy are readily actionable with average hormone levels of insulin/ghrelin/leptin etc.) when consuming carbohydrates, but can turn to other nutrient sources when they are not to be found.
4. Our body composition can be manipulated by manipulating our energy expenditure either via manipulating the caloric content of food or via the preferential production of body tissue from horomonal influence (this is why muscle mass increases when using testosterone even if caloric intake is kept constant but above a certain macronutrient threshold).
5.There are a certain set of micronutrients we need on a continuous basis (the exact amounts of which are up for debate but the ranges seem to be reasonably agreed upon).
6. Our diet influences our gut fauna and this further influences how much nutritional value we get from our diet, it is quite a symbiotic cycle.
7. Barring certain specific horomonal imbalance diseases, everyone's body largely abides by the above principles, (i.e as special as everyone thinks they are, they're probably more average than not when it comes their metabolism).