1. The six nutrients needed by human body mainly include sugar, fat, protein, water, inorganic salts and vitamins.

2. Among them, water and inorganic salts are small molecules of inorganic substances, which contain no carbon and cannot be burned to provide energy for human body.

3. Sugar, fat, protein and vitamins are all macromolecular organic substances, among which sugar, fat and protein can provide energy for human body.