it likely doesnt violate thermodynamics since caloric intake isn't likely to be super representative of actual converted energy. Likewise, an individuals energy consumption is also likely to vary as well, even in the case of certain consumed foods. Wouldn't suprise me if there was data suggesting asian people consumed food in a marginally different manner to american people, for example. There are just certain things the body adapts to, and over time engages with biased selection for.