Will you be estimating the gross energy or the physiologic energy value of a peanut when you do the calculations for this experiment?

I believe it would be the gross energy.

Gross energy could be easily estimated by calculating the mass of fat, protein, and carbs. In order to estimate the physiologic energy, you need to measure the exact calories that the subject would most likely spent in doing all of his/her activities. This kind of thing would be really difficult to do in an experiment.