The Five Food Principles
For convenience of comparison foods may be divided into five classes: Water, Protein, Fats, Carbohydrates, Mineral Matters.
Some scientists include air in the list, but it has been thought best in this work to speak of it separately as the greatest necessity of life, but not in the sense of a direct nutrient.
An average composition of three of the principles is as follows:
| { | Carbon | 53 | |
| Protein | { | Hydrogen | 7 |
| { | Oxygen | 24 | |
| { | Nitrogen | 16 | |
| { | Carbon | 76.5 | |
| Fats | { | Hydrogen | 12 |
| { | Oxygen | 11.5 | |
| { | Nitrogen | — | |
| { | Carbon | 44 | |
| Carbohydrates | { | Hydrogen | 6 |
| { | Oxygen | 50 | |
| { | Nitrogen | — |
It will be seen from the above that the protein compounds contain nitrogen; the fats and carbohydrates do not.