TL;DR: “ the first law holds even in irreversible processes – energy is still conserved – the second law says that something is lost, something is unrecoverable

TL;DR: “ the first law holds even in irreversible processes – energy is still conserved – the second law says that something is lost, something is unrecoverable (..) The efficiency of a machine is dependent on how the machine works and, for a biochemical machine, the nature of the fuel and the processes enlisted by the organism. (..) In weight loss diets, of course, inefficiency is desirable and is tied to hormonal levels and enzyme activities. (..) The second law of thermodynamics says that variation of efficiency for different metabolic pathways is to be expected. Thus, ironically the dictum that a "calorie is a calorie" violates the second law of thermodynamics, as a matter of principle.” About the above text: Tried to cut parts from the article to abstract the main points.