Fats and proteins yield more energy than carbohydrates do. Lipids do not dissolve well in water because of their non-polar character. Because fats can be stored without water, lipids yield more energy than water stored carbohydrates. Thus, we predicted that substances containing primarily fats and oils would have less water content but more calories. There was no visible correlation between the water content of protein-rich foods and the energy yield.
Proteins are polypeptides consisting of many amino acids.
We reasoned that water content of protein-rich foods may not be used to determine the calories in the food. We reasoned that substances containing primarily carbohydrates metabolize essentially sugars. From this, substances containing large quantities of carbohydrates would have more water soluble vitaimins. It is possible that moisture may have been trapped within the samples, but the overnight heating appeared to be sufficient in evaporating nearly all the water. Quer, P. Font, The Anatomy of Plants , Harper and Brothers, New York, NY 1960.