About your question 1: Your brain can't be charged by any kind of sugar. Contains all nutrients. Skipping breakfast doesn't just affect your brain. What is more directly affected is your liver, stomach and injury, which can easily lead to stomach diseases, lithiasis and liver diseases. Women can also harm the uterus and affect fertility.
Question 2: protein doesn't mean that it has any physiological function. It's about the operation of your whole body and organs. You need protein all over your body. As for why to beautify the skin, it also involves protein's effect on various organs of the body. The reason to beautify the skin stems from the influence on the liver, and at the same time, it can make the muscles and skin firm and get beautiful skin.
Question 3: Fat not only provides heat for the body, but also transforms into nutrients needed by the body (the transformation function needs the cooperation of other nutritional conditions).
It can also strengthen organs and reduce gravity for organs. Secondly, excessive intake directly leads to obesity, which also increases the pressure of liver fat metabolism. Obesity can lead to fatty liver, hyperlipidemia and hypertension. . .
Question 4: There are many kinds of vitamins, A, B, C, D, E,,,, and so on. B is divided into B 12,,, and there are many others.
Question 5: Trace elements include calcium, iron, zinc, copper and beauty.
Finally, I want to tell you. The question you asked involves the whole nutrition, and you can't figure it out by just a few questions here.
If you want to know more. It is recommended to read systematic nutrition books.