What's the term for energy that is/isn't usable by an organism?

Question

Every healthy organism stores some of its biochemical energy in reserves (e.g. adipose tissue, glycogen), but much of an organism's biochemical energy is bound in ways that aren't normally accessible to it (e.g. protein in muscles or vital organs).

The latter quantity has some thermodynamic implications. For example, the inaccessible energy can be transferred to a predator if the organism is eaten, and a fetus's inaccessible energy must be obtained from its mother.

To research these concepts, I'm looking for a term for energy that's accessible by the organism and a term for energy that's not accessible by the organism.

I've searched the web (and StackExchange specifically) for a variety of terms, (e.g. "expendable", "reserved", "essential", "innate", etc.) but none of them produced relevant results.

Answer 1

I have been working on nonequilibrium thermodynamics related to life and its implications for Hegelian philosophy and this concept you describe is quite interesting. Imagining that there is a being, an agent, that takes advantage of a certain mass for its survival, the simplest term would be "metabolize", from the Greek μεταβολή (change, transformation) with the suffix indicating transformation.

While metabolizable is a generic term for using something, I have distinguished between two varieties of metabolization. On the one hand, simple catabolization, decomposition into smaller parts for structural reuse, from the Greek καταβολή. Literally, καταβολή means to throw down. This "throw" is somewhat strange, but as it is an established term, it is better to use it.

On the other hand, the use as a mere energy resource, we should use "trophic", from τροφή (trophē): "feeding" or "nutrition," derived from the verb "τρέφω" (trépho), which means "to feed" or "to nourish.", giving metatrophism to the mere feeding without integrating into the body structure.

Finally, let's see how to adapt this nomenclature to describe the concepts of your research, of things that are beyond the reach of use as energy:

• Parathrophic (parathrophizable) - unsuited to use as food (such as sand).
• Parametabolic (parametabolizable) - unsuited to decompose to use as structural elements (such as meat for vegetarians).
• Paracatabolic (paracatabolizable) - unsuited to decompose (such as cellulose for humans).

Hope this helps with the nomenclature in your research!

Answer 2

I assume that, as suggested by the original form of this question and the comments requesting clarification, that the interest is in the energy a carnivorous animal predator can obtain from its killed prey. In this case, the most appropriate terms to describe this would seem to be those employed by nutritionalists. From a perusal of this topic in various Wikipedia articles I find no internationally recognized phrase, but would suggest the following as consistent with the terminology in this field:

Dietary Energy Equivalent

The use of the word “dietary” (or something similar) is important as it makes it clear that one is not concerned with the energy reserves that the living animal deposits for its own use, although these obviously contribute to the ‘dietary energy equivalent’.

(One of the Wikipedia articles that prompted this suggestion was: https://en.wikipedia.org/wiki/List_of_countries_by_food_energy_intake — a table heading therein.).